[Federal Register: December 10, 2002 (Volume 67, Number 237)]
[Proposed Rules]
[Page 76055-76094]
From the Federal Register Online via GPO Access [wais.access.gpo.gov]
[DOCID:fr10de02-19]
[[Page 76055]]
-----------------------------------------------------------------------
Part VII
Department of Health and Human Services
-----------------------------------------------------------------------
Food and Drug Administration
-----------------------------------------------------------------------
21 CFR Part 1020
Electronic Products; Performance Standard for Diagnostic X-Ray Systems
and Their Major Components; Proposed Rule
[[Page 76056]]
-----------------------------------------------------------------------
DEPARTMENT OF HEALTH AND HUMAN SERVICES
Food and Drug Administration
21 CFR Part 1020
[Docket No. 01N-0275]
RIN 0910-AC34
Electronic Products; Performance Standard for Diagnostic X-Ray
Systems and Their Major Components
AGENCY: Food and Drug Administration, HHS.
ACTION: Proposed rule.
-----------------------------------------------------------------------
SUMMARY: The Food and Drug Administration (FDA) is proposing to amend
the performance standard for diagnostic x-ray systems and their major
components. The agency is taking this action to update the standard to
account for changes in technology and use of radiographic and
fluoroscopic systems as well as to fully utilize the currently accepted
metric system of units in the standard. For clarity and ease of
understanding, FDA is republishing the complete contents of the
affected regulations. This action is being taken under the Federal
Food, Drug, and Cosmetic Act (the act), as amended by the Safe Medical
Devices Act of 1990 (SMDA).
DATES: Submit written or electronic comments by April 9, 2003. See
section III of this document for the proposed effective date of a final
rule based on this document. Submit written comments on the information
collection requirements by January 9, 2003.
ADDRESSES: Submit written comments to the Dockets Management Branch
(HFA-305), Food and Drug Administration, 5630 Fishers Lane, rm. 1061,
Rockville, MD 20852. Submit electronic comments to http://www.fda.gov/dockets/ecomments.
Submit written comments regarding the information
collection requirements to the Office of Information and Regulatory
Affairs, Office of Management and Budget (OMB), New Executive Office
Bldg., 725 17th St., NW. rm. 10235, Washington, DC 20503, Attn: Desk
Officer for FDA.
FOR FURTHER INFORMATION CONTACT: Thomas B. Shope, Center for Devices
and Radiological Health (HFZ-140), Food and Drug Administration, 9200
Corporate Blvd., Rockville, MD 20850, 301-443-3314, ext. 132.
SUPPLEMENTARY INFORMATION:
Table of Contents
I. Background
II. Proposed Amendments to the Performance Standard for Diagnostic X-
Ray Systems and Their Major Components
A. Change in the Quantity Used to Describe X-Radiation From
Exposure to Air Kerma
B. Clarification of Applicability of Requirements to Account for
Technological Developments in Fluoroscopic X-Ray Systems Such as
Digital Imaging, Digital Recording, and New Types of Solid-State X-Ray
Imaging Devices
C. Changes and Additions to Definitions and Applicability
Statements
D. Information to be Provided to Users (Sec. 1020.30(h))
E. Increase in Minimum Half-Value Layer (Sec. 1020.30(m)(1))
F. Change in the Requirement for Fluoroscopic X-Ray Field
Limitation and Alignment (Sec. 1020.32(b))
G. Revisions and Change in the Limits to Maximum Air Kerma Rate
(Sec. 1020.32(d) and (e))
H. New Modes of Image Recording
I. Entrance Air Kerma Rate at the Fluoroscopic Image Receptor
J. Requirement for Minimum Source-Skin Distance for Small C-Arm
Fluoroscopic Systems (Sec. 1020.30(g))
K. Requirements for Display of Fluoroscopic Irradiation Time, Air
Kerma Rate, and Cumulative Air Kerma (Sec. 1020.32(h) and proposed
(k))
L. ``Last-Image Hold'' Feature on Fluoroscopic Systems (Proposed
Sec. 1020.32(j))
M. Modification of Previously Manufactured and Certified Equipment
N. Modification of Warning Label (Sec. 1020.30(j))
O. Corrections of Sec. 1020.31(f)(3) and (m)
P. Corrections to Reflect Changes in Organizational Name, Address,
and Law (Sec. 1020.30(c), (d), and (q))
Q. Removal of Reference to Special Attachments for Mammography
R. Change to the Applicability Statement for Sec. 1020.32
S. Republication of Sec. Sec. 1020.30, 1020.31, and 1020.32
III. Proposed Effective Date
IV. Environmental Impact
V. Paperwork Reduction Act of 1995
VI. Analysis of Impacts
A. Introduction
B. Objective of the Proposed Rule
C. Risk Assessment
D. Constraints on the Impact Analysis
E. Baseline Conditions
F. The Proposed Amendments
G. Benefits of the Proposed Amendments
H. Estimation of Benefits
I. Costs of Implementing the Proposed Regulations
J. Small Business Impacts
K. Reporting Requirements and Duplicate Rules
L. Conclusion of the Analysis of Impacts
VII. Federalism
VIII. Submission of Comments
IX. References
I. Background
The SMDA (Public Law 101-629) transferred the provisions of the
Radiation Control for Health and Safety Act of 1968 (RCHSA) (Public Law
90-602) from title III of the Public Health Service Act (PHS Act) (42
U.S.C. 201 et seq.) to chapter V of the act (21 U.S.C. 301 et seq.).
Under the act, FDA administers an electronic product radiation control
program to protect the public health and safety. FDA also develops and
administers radiation safety performance standards for electronic
products.
The purpose of the performance standard and these proposed
amendments is to improve the public health by reducing exposure to and
the detriment associated with unnecessary ionizing radiation from
diagnostic x-ray systems while assuring the clinical utility of the
images.
In order for mandatory performance standards to provide the
intended public health protection, the standards must be modified when
appropriate to reflect changes in technology or product usage. A number
of technological developments have been or will soon be implemented for
radiographic and fluoroscopic x-ray systems. Such developments,
however, are not addressed in the current standard, but have presented
problems in the application of the current performance standard.
FDA thus is proposing to amend the performance standard for
diagnostic x-ray systems and their major components in Sec. Sec.
1020.30, 1020.31, 1020.32, and 1020.33(h) (21 CFR 1020.30, 1020.31,
1020.32, and 1020.33(h)).
These proposed amendments will require additional features on newly
manufactured x-ray systems that physicians may use to minimize x-ray
exposures to patients. Advances in technology have made several of
these newly required features possible or feasible at minimal cost.
In the Federal Register of August 15, 1972 (37 FR 16461), FDA
issued a final rule for the performance standard, which became
effective on August 1, 1974. Since then, FDA has made several
[[Page 76057]]
amendments to the performance standard to incorporate new technology,
to clarify misinterpreted provisions, or to incorporate additional
requirements necessary to provide for adequate radiation safety of
diagnostic x-ray systems. (See, e.g., amendments published on October
7, 1974 (39 FR 36008); February 25, 1977 (42 FR 10983); September 2,
1977 (42 FR 44230); November 8, 1977 (42 FR 58167); May 22, 1979 (44 FR
29653); August 24, 1979 (44 FR 49667); November 30, 1979 (44 FR 68822);
April 25, 1980 (45 FR 27927); August 31, 1984 (49 FR 34698); May 3,
1993 (58 FR 26386); May 19, 1994 (59 FR 26402); and July 2, 1999 (64 FR
35924)).
In the Federal Register of December 11, 1997 (62 FR 65235), FDA
issued an advance notice of proposed rulemaking requesting comments on
the proposed conceptual changes to the performance standard. The agency
received 12 comments from State and local radiation control agencies,
manufacturers, and a manufacturer organization. FDA considered these
comments in developing this proposal. In addition, the concepts
embodied in these proposed amendments were discussed on April 8, 1997,
during a public meeting of the Technical Electronic Product Radiation
Safety Standards Committee (TEPRSSC). TEPRSSC is a statutory advisory
committee (21 U.S.C. 360kk(f)(1)(A)) that FDA is required to consult
before it may prescribe any electronic product performance standard
under the act. The proposed amendments themselves were discussed in
detail with the TEPRSSC during its meeting on September 23 and 24,
1998. TEPRSSC approved the content of the proposed amendments and
concurred with their publication for public comment.
The proposed amendments described in section II of this document
may be considered as nine significant amendments to the current
standard and several other minor supporting changes, corrections, or
clarifications. The nine principal amendments fall into the following
three categories:
1. Amendments requiring changes to equipment design and performance;
2. Amendments designed to improve use of fluoroscopic systems by
requiring enhanced information to users; and
3. Amendments applying the standard to new features and technologies
associated with fluoroscopic systems.
II. Proposed Amendments to the Performance Standard for Diagnostic X-
Ray Systems and Their Major Components
A. Change in the Quantity Used to Describe X-Radiation From Exposure to
Air Kerma
FDA proposes to change the quantity and the associated unit used to
describe the radiation emitted by the x-ray tube or absorbed in air.
The radiation quantity ``exposure'' would be replaced by the quantity
``air kerma.'' The units used to describe these quantities would be
changed accordingly throughout the standard, wherever appropriate.
The International System of Units (SI) was named and adopted at the
11th General Conference on Weights and Measures (GCWM) in 1960 as an
extension of the earlier metric systems. The SI, also referred to as
the metric system, is the approved system of units for use in the
United States. The U.S. Department of Commerce published an
``Interpretation and Modification of the International System of Units
for the United States'' in the Federal Register on December 10, 1976,
which set forth the interpretation of the SI system for the United
States. The Omnibus Trade and Competitiveness Act of 1998 amended the
Metric Conversion Act of 1975 to require each Federal agency to use the
metric SI system in its activities. The FDA policy for use of metric
measurements is described in a March 19, 1990, memorandum. This policy
calls for use of the metric units followed by a parenthetic ``inch-
pound'' declaration unless there is a cogent reason not to utilize dual
metric and ``inch-pound'' measurements. The policy notes that there
should be few such exceptions.
One of the objectives of the International Commission on Radiation
Units and Measurements (ICRU) is to develop internationally accepted
recommendations regarding quantities and units of radiation and
radioactivity. The ICRU recommendations often form the basis of GCWM
actions. In 1998, the ICRU published its Report 60, ``Fundamental
Quantities and Units for Ionizing Radiation,'' superseding its previous
Report 33. Report 60 uses the SI units and special names for some
radiation units (Ref. 1). The ICRU had suggested phasing out by 1985
the use of certain special quantities and units that were not part of
the SI system, including the special unit of exposure, the roentgen
(R).
The current Federal performance standard for diagnostic x-ray
equipment uses the special quantity exposure to describe the radiation
emitted from an x-ray system. In the Federal Register of May 3, 1993
(59 FR 26386), FDA published a final rule which made a partial
transition to the SI units by changing the unit for exposure from
``roentgen'' (R) to ``coulomb per kilogram'' (C/kg). This change
required using an awkward conversion factor of 2.58 x 10-4
C/kg per R.
In view of current trends, scientific practice, the U.S. policy,
and FDA directives, FDA proposes that a complete conversion be made to
the SI quantities and units by amending the standard to require using
the quantity air kerma in place of the quantity exposure. Additionally,
the agency proposes that, in making this conversion, the absolute
magnitude of the limits on radiation contained in the standard not be
changed. This requires that the limits, when expressed in the new
quantity air kerma and its unit, the gray, be expressed with numerical
values different from the current limits that use the quantity
exposure.
In its recent reports, the National Council on Radiation Protection
and Measurement (NCRP) adopted the use of the SI quantity kerma, in
particular air kerma, to describe the radiation emitted from an x-ray
system. This change in the NCRP recommendations was made without
significant concern that previous limits in the voluntary
recommendations were slightly increased by this change when numerical
values for the limits were not changed but were expressed in the new
units. This change in the NCRP recommendations resulted in an increase
in the limits, compared to previous recommendations, of about 15
percent.
FDA is not proposing such an increase in this proposal. Instead,
FDA is proposing that the numerical values for limits in the standard
relating to radiation, when expressed in the new quantity, be changed
as well so the new limits will be equivalent to the current limits,
thereby making no change to the level of radiation protection provided
by the standard. FDA has dropped earlier draft proposals to change the
numerical values in a manner similar to the changes made to the
voluntary recommendations by the NCRP because of several comments that
were received. The comments objected to any changes to the level of
radiation protection provided by the limits in the current mandatory
standard.
This proposed approach to the numerical limits results in numerical
values that are not integer numbers or multiples of 5 or 10, as is the
case in the current standard, when limits are expressed in the non-SI
unit for
[[Page 76058]]
exposure, roentgen. For example, the current limit for an exposure rate
of 10 R/minute (R/min), 2.58 x 10-3 C/kg per min, becomes an
air kerma rate (AKR) limit of 88 milligray per minute (mGy/min) under
the proposed approach.
FDA is proposing new definitions of the quantities kerma, as used
by the ICRU, and air kerma in Sec. 1020.30(b). Because the quantity
air kerma is a different quantity from exposure and not numerically
equivalent, FDA is proposing in the amended standard to express the
limits in terms of air kerma and indicate the equivalent limit in terms
of exposure using the word ``vice'' to indicate this equivalence. Thus,
the change described above would be given in the proposed amendments as
a limit expressed as ``88 mGy/min (vice 10 R/min)'' indicating that the
new limit of 88 mGy/min air kerma is equivalent to the previous limit
10 R/min exposure.
Current International Electrotechnical Commission (IEC) standards
for diagnostic x-ray systems use the quantity air kerma to describe the
radiation emitted by the x-ray system. The current limits on maximum
fluoroscopic exposure rates in the performance standard were
established to be consistent with the recommendation of the NCRP. The
proposed amendment maintains agreement between the performance standard
and the voluntary standards in terms of the quantities and units used.
But in order to maintain the current level of radiation protection and
in response to the comments received, the change results in numerical
limits for some of the requirements different from those used in the
current recommendations of the NCRP.
The term ``exposure'' is also used with a second meaning in the
performance standard that does not refer to a quantity of radiation as
defined here. The second meaning of ``exposure'' refers to the process
or condition during which the x-ray tube is activated by a flow of
current to the anode and radiation is produced. The second meaning of
exposure will continue to be used where appropriate. FDA is proposing
to revise the definition of the quantity exposure in Sec. 1020.30(b)
to match the current ICRU definition.
FDA also proposes in Sec. 1020.30(b) to amend the definitions of
``half-value layer'' (HVL) and ``x-ray field'' to reflect the change
from the quantity exposure to air kerma.
B. Clarification of Applicability of Requirements to Account for
Technological Developments in Fluoroscopic X-Ray Systems Such as
Digital Imaging, Digital Recording, and New Types of Solid-State X-Ray
Imaging Devices
When the performance standard was originally developed, the only
means for producing a fluoroscopic image was either a screen of
fluorescent material or an x-ray image intensifier tube. Thus, the
standard was originally written with these two types of image receptors
in mind. The advent of new types of image receptors, such as solid-
state x-ray imaging (SSXI) devices, and new modes of image recording,
such as digital recording to computer memory or other media, has made
the application of the current standard to systems incorporating these
new technologies cumbersome and awkward. These new aspects of
fluoroscopic system design have required a series of interpretations to
apply the standard appropriately. With this in mind, FDA proposes to
amend the performance standard to recognize these new types of image
receptors and modes of image recording and to clarify how the
requirements of the standard apply in each case. This amendment would
result in replacing the terms ``x-ray image intensifier'' or ``image
intensifier'' with the more general term ``fluoroscopic image
receptor'' in numerous sections.
Although the basic radiation protection and safety requirements for
fluoroscopic equipment in the performance standard are based on the
presence of an x-ray image intensifier, these requirements are also
appropriate for newer imaging systems that do not use an x-ray image
intensifier. The newer imaging systems may incorporate an image
receptor consisting of an absorbing material and an array of solid
state transducers that intercepts x-ray photons and directly converts
the photon energy into a modulated electrical signal. The signal often
goes through analog-to-digital conversion as part of the image
formation process to perform both fluoroscopy and radiography. FDA
proposes to modify the structure and organization of the standard to
address this new type of x-ray imaging equipment. The specific changes
proposed are described below in section II.C of this document.
For SSXI, new performance considerations are relevant because of
the different construction and the use of solid-state materials such as
silicon and selenium. These new considerations include: Changes in
spatial resolution, as quantified in the modulation transfer function
(MTF), dynamic range, and detective quantum efficiency; the
introduction of aliasing artifacts; reduced geometrical efficiency
(fill factor); and differences in the range of quantum-limited
operation when compared to the older vacuum-tube-based fluoroscopic
equipment. Because consensus is not available on some aspects of the
performance for these new devices, the agency has relied on premarket
review and associated guidance documents to provide the necessary
radiation safety control for these devices. (See, e.g., the ``Guidance
for the Submission of 510(k)s for Solid State X-Ray Imaging Devices ''
(Ref. 2).)
An example of a new performance consideration for the SSXI is the
active detector area. Because of the need for electrical separation/
insulation between individual detector elements, the detector area has
both active and inactive regions, in terms of detecting image
information. The relative areas of the active and inactive detector
areas are usually described in terms of the fill factor. The fill
factor, to a first approximation, is the pixel area (active area in
terms of image formation) times the number of pixels divided by the
total detector area exposed to the input image flux.
The fill factor and other characteristics can have significant
effects on imaging performance. The imaging performance must also be
considered when obtaining a complete picture of the effectiveness of
these devices. Although FDA is not offering specific proposals for
imaging performance at this time, FDA is inviting comment on possible
approaches to ensuring radiation protection and safety in the
application of these SSXI devices.
C. Changes and Additions to Definitions and Applicability Statements
To address the changes in technology and the new types of image
receptors and to allow these items to be appropriately integrated into
the standard, FDA proposes the following changes in definitions and
applicability sections of the standard. The changes in definitions
described here are in addition to those described above in section II.A
of this document.
First, in Sec. 1020.30(b), FDA proposes to amend the definition of
``fluoroscopic imaging assembly,'' ``image receptor,'' ``spot-film
device,'' and ``x-ray table'' by removing the reference to an x-ray
image intensifier as the descriptor of the image receptor or by
replacing image intensifier with the more general term fluoroscopic
image receptor.
[[Page 76059]]
Second, FDA also proposes in Sec. 1020.30(b) to amend the
definition of the term ``recording'' by removing the word ``permanent''
and replacing it with the word ``retrievable,'' and to remove the
examples of ``recording,'' to clarify the definition of the term
``recording'' in the context of images stored on recording media other
than film.
Third, in Sec. 1020.30(b), FDA proposes to clarify the
applicability of the standard or to bring precision to the meaning of
specific requirements by adding definitions for the terms solid state
x-ray imaging device, fluoroscopy, radiography, non-image intensified
fluoroscopy, automatic exposure rate control, isocenter, last image
hold (LIH) radiograph, mode of operation, and source-skin distance
(SSD).
Last, under Sec. 1020.30(b), FDA proposes to add a definition of
``lateral fluoroscope'' to clarify the distinction between a lateral
fluoroscope and what is commonly referred to as a C-arm fluoroscope. In
an August 29, 1977, Compliance Policy Guide, FDA described the geometry
for measuring, during a compliance test, the entrance exposure rate for
lateral fluoroscopes. The standard does not define a system by the way
it is used but allows the manufacturer to specify the use for which the
equipment is designed. The design of the system determines whether the
system is a C-arm or a lateral fluoroscope. If the system is a C-arm,
it is tested using the test geometry for a C-arm system, even if it is
used with a lateral beam direction. If the system is a dedicated
lateral fluoroscope used with a biplane system, the more restrictive
measurement geometry, as described for a lateral fluoroscope in the
current Sec. 1020.32(d)(4)(iv) and (e)(3)(iv), will be used. This test
geometry is described in proposed Sec. 1020.32(d)(3)(v).
The lateral fluoroscope consists of a support structure holding a
tube housing assembly and a fluoroscopic imaging assembly with the x-
ray beam in a lateral projection parallel to the plane of the tabletop.
Thus, the geometry of the source and image receptor is fixed relative
to the patient or x-ray table. The entrance air kerma would be measured
with the radiation measurement instrument detector placed 15
centimeters (cm) from the center of the table in the direction toward
the x-ray source. (This position is considered to be typical of the
entrance skin surface of the patient.) During the measurement, the tube
housing assembly is positioned as close to this location as allowed by
the system. For C-arm system measurement geometry, the patient is
assumed to be as close to the image receptor as possible and,
therefore, the detector is placed 30 cm from the entrance surface of
the image receptor. In a lateral fluoroscope, the patient cannot be
placed against the image receptor, and the measurement point is
referenced to the center of the table. The standard does not require
that the table have the centerline indicated. Testing is performed
relative to the centerline and the center is located by measurement if
necessary.
Additionally, FDA proposes to correct two minor typographical
errors that were introduced into the definitions of ``leakage technique
factors'' and ``spot-film device'' in the May 3, 1993, Federal
Register.
FDA proposes in Sec. Sec. 1020.31 and 1020.32 to amend the
applicability statements by removing the reference to an x-ray image
intensifier as the descriptor of the image receptor used to distinguish
between radiography and fluoroscopy. FDA proposes to further modify the
applicability statements to clearly identify the type of x-ray imaging
equipment to which each section applies and to distinguish between
radiographic and fluoroscopic imaging.
Additionally, to complete the transition to the use of the
terminology ``fluoroscopic image receptor,'' FDA proposes in Sec.
1020.32(a)(1) and (a)(2), to replace the term ``image intensifier''
with the more inclusive term ``fluoroscopic image receptor'' to reflect
the changes in fluoroscopic image receptor technology and design. This
change will, therefore, include SSXI devices, x-ray image intensifiers,
and other fluoroscopic image receptors within the transmission limit
and measurement criteria of paragraphs (a)(1) and (a)(2).
Similarly, FDA proposes in Sec. 1020.32(g) to remove ``image-
intensified fluoroscope'' and add in its place the generic term
``fluoroscope'' in the description of the requirement for minimum SSD
for systems intended for specific surgical applications.
Finally, in Sec. 1020.32(i), FDA proposes to remove the term
``intensified imaging'' and add in its place ``image receptor
incorporating more than a simple fluorescent screen.'' This removes the
reference to a specific type of fluoroscopic image receptor, the image
intensifier, and includes all types of receptors other than a simple
fluorescent screen as meeting the requirement of Sec. 1020.32(i).
D. Information to be Provided to Users (Sec. 1020.30(h))
FDA proposes to add two paragraphs to Sec. 1020.30(h). Proposed
Sec. 1020.30(h)(5) and (h)(6) would require manufacturers to provide
in the instructions for users additional information regarding
fluoroscopic x-ray systems.
Recent developments in the technology of fluoroscopic systems have
resulted in equipment being increasingly provided with a variety of
special modes of operation and methods of recording fluoroscopic
images. Some of these modes of operation may significantly increase the
entrance AKR to the patient compared to conventional fluoroscopy. There
is concern that the operating instructions provided with the
fluoroscopic system lack sufficient information concerning the
characteristics of these special modes of operation to permit the
operator to adequately evaluate the increased radiation output and
consequent increased exposure to the patient and operator from these
modes of operation. There is typically little information provided to
users on the clinical procedure(s) for which each mode was designed,
resulting in potential inappropriate application of the mode by a user
who is not fully aware of the intended application of the particular
mode of operation.
Proposed Sec. 1020.30(h)(5) would require that the information
provided to users contain a detailed description of each mode of
operation and specific instructions on the manner in which the mode is
engaged or disengaged. The manufacturer would also be required to
provide information on the specific types of clinical procedures or
imaging tasks for which the mode is intended and instructions on how
each mode should be used. This information is to be provided in a
special section of the user's instruction manual or in a separate
manual devoted to this purpose.
Section 1020.30(h)(1)(i) of the performance standard states that
the information to users shall contain ``Adequate instructions
concerning any radiological safety procedures and precautions which may
be necessary because of unique features of the equipment * * *.'' FDA
considers any mode of operation that yields an entrance AKR above 88
mGy/min to be a unique feature of the specific fluoroscopic equipment
and thus must have a full and complete description in the instructions
for its use.
FDA is also of the opinion that, for modes of operation where the
entrance
[[Page 76060]]
AKR exceeds 88 mGy/min, the manufacturer should provide detailed
information to permit the user to assess the exposure to the patient
relative to that delivered in the normal mode of operation. Such
information would give operators important radiation safety data with
which to make better judgments on the possible hazards involved with a
particular procedure. FDA has learned that, because of the multiple
number of modes and options available with many of the systems, many
users are not aware of when or how such modes are engaged and
disengaged or the radiation output consequences of such modes. FDA had
originally considered requiring the manufacturer to provide data on the
entrance AKRs for each mode of operation of the fluoroscopic system.
However, the large number of possible combinations of modes and options
for operation available with many of the systems makes this
impractical. The proposed amendment described in section II.J of this
document would require the manufacturer to provide a display of the AKR
and cumulative air kerma. With this information, the user is made aware
of the relative changes in the AKR when changing from one mode of
operation to another. Awareness of such changes will inform the user of
the relative output changes of the system as a function of mode of
operation, patient size, and system geometry.
FDA believes that manufacturers are already providing much of the
information proposed in this requirement. However, the information may
not be displayed in a separate section of the manual where users can
readily find it, and the information may not contain enough detailed
information on the intended use of the various modes of operation to
assure proper use of the system.
Proposed Sec. 1020.30(h)(6) would require manufacturers to provide
users with information regarding the new features of fluoroscopic
systems described in proposed Sec. 1020.32(k). Proposed Sec.
1020.30(h)(6) would also require manufacturers to provide information
regarding the display of values of AKR and cumulative air kerma. This
information will include a statement of the maximum deviation of the
actual values of AKR and cumulative air kerma from their displayed
values, maintenance and instrumentation calibration information, and a
description of the spatial coordinates of the reference location for
which the displayed values are given.
E. Increase in Minimum Half-Value Layer (Sec. 1020.30(m)(1))
FDA proposes to modify the requirement for minimum HVL to recognize
changes in x-ray tube and x-ray generator technology over the last few
decades.
The use of x-ray filtration to increase the quality or homogeneity
of an x-ray beam through selective absorption of the low energy photons
has been a recommended practice for a long time. A 1968 report
published by NCRP (appendix B, table 3, in Ref. 3) provides the beam
quality in terms of HVL, as a function of tube potential, that would
result from specified values of total x-ray filtration in the x-ray
beam. However, the values of HVL in the table would only result if one
used the NCRP suggested values of total filtration in diagnostic x-ray
equipment of that era (i.e., the 1960s to early 1970s). It should be
noted that diagnostic x-ray equipment of that era was characterized by
x-ray tubes with a large x-ray target angle and x-ray generators with
significant ripple in the high voltage waveform (e.g., an x-ray target
angle of 22[deg] and a high voltage ripple of 25 percent).
The requirements on beam quality in the current IEC international
standard (Ref. 4) are also expressed in a similar manner as the NCRP
Report No. 33 (i.e., a total filtration requirement plus a set of
minimum HVL values). The Institute of Physical Sciences in Medicine has
recently published a report which can be used to estimate the total
filtration from HVL data as a function of x-ray target angle and high
voltage ripple (Ref. 5). These data point out the lack of
correspondence between a total filtration of 2.5 millimeters (mm) of
aluminum and the minimum HVL requirements in the performance standard
for state-of-the-art x-ray equipment (e.g., an x-ray target angle of
12[deg] and a high voltage ripple of 10 percent). For these types of
equipment, the minimum HVL requirements in the performance standard can
be met with about 1.8 mm of total filtration versus the required 2.5 mm
of total filtration as specified in the IEC standard (Ref. 4). Only
equipment with large x-ray target angles (22[deg]) and a great deal of
high voltage ripple (25 percent) need a total filtration of 2.5 mm of
aluminum to meet the minimum HVL requirements in the performance
standard. In terms of skin-sparing effect, the performance-oriented set
of minimum HVL values in the performance standard have not kept up with
changes in x-ray equipment when compared to the design-oriented
requirement of a total filtration of 2.5 mm of aluminum.
For these reasons, FDA proposes to increase the minimum HVL values
for radiographic and fluoroscopic equipment excluding mammography
equipment and dental equipment designed for use with intraoral image
receptors. The proposed minimum HVL values represent the values
obtained with a total filtration of 2.5 mm of aluminum on state-of-the-
art diagnostic x-ray equipment (i.e., an x-ray target angle of 12[deg]
and a high voltage ripple of 10 percent). FDA used the data in the
Institute of Physical Sciences in Medicine report to arrive at the
proposed minimum HVL values.
As a separate x-ray filtration issue, there has been a substantial
increase over the past 20 years in the use of x-ray fluoroscopy as a
visualization tool for a wide range of diagnostic and therapeutic
procedures. Because of the long catheter manipulation times and the
need, in some cases, for a stationary x-ray field, these procedures
have the potential, sometimes realized, for high radiation dose to
patients and clinical personnel (Ref. 6). In fact, the agency has been
actively involved in promoting recommendations for the avoidance of
serious, x-ray-induced, skin injuries to patients during
fluoroscopically-guided interventional procedures. As a result, there
continues to be an interest in dose reduction techniques for these
procedures.
In general, the addition of either beam-hardening or K-edge x-ray
filters can provide a significant reduction in the exposure,
particularly skin exposure, to the patient. However, this reduction in
exposure is accompanied by an attendant increase in tube load (Ref. 7).
It should be noted that one of the recommendations of the work group on
the technical aspects of fluoroscopy at the 1992 American College of
Radiology (ACR)/FDA workshop on fluoroscopy (Ref. 8) was to increase
the minimum HVL. Therefore, FDA is also proposing an additional
requirement for fluoroscopic x-ray systems incorporating x-ray tubes of
high heat-load capacity. Manufacturers of these systems would be
required to provide a means, at the user's option, for adding
additional x-ray filtration over and above the amount needed to meet
the proposed new minimum HVL values. This requirement is based on the
assumption that x-ray tubes with high heat-load capacity are typically
required or provided on equipment designed for use in interventional
procedures due to the imaging task requirements and the extended
exposure times associated with interventional procedures. The
[[Page 76061]]
method of implementation and the actual values of additional filtration
to realize the reduction in skin exposure will be left to the
discretion of the manufacturer.
F. Change in the Requirement for Fluoroscopic X-Ray Field Limitation
and Alignment (Sec. 1020.32(b))
FDA proposes to reorganize and add new paragraphs to Sec.
1020.32(b) to require improved x-ray field limitation for fluoroscopic
x-ray systems. Section 1020.32(b) would be reorganized to retain the
current requirements applicable to systems manufactured before the
effective date of these amendments. For systems manufactured after the
effective date, new requirements are proposed in Sec. 1020.32(b)(4)
and (b)(5) respectively, for systems with inherently circular or
rectangular image receptors. These proposed new requirements will
result in increased geometric efficiency or more efficient use of
radiation as described below.
The proposed reorganization and retention of the existing
requirements in Sec. 1020.32(b) will be accomplished in the following
manner: Section 1020.32(b)(1)(i) will be redesignated as Sec.
1020.32(b)(3); Sec. 1020.32(b)(1)(ii) and (b)(2)(iii) will be combined
and redesignated as Sec. 1020.32(b)(1) with appropriate revisions to
paragraph references to reflect the reorganization of Sec. 1020.32(b);
Sec. 1020.32(b)(2)(iv) will be redesignated as Sec. 1020.32(b)(2)
with a minor clarification; and Sec. 1020.32(b)(3) will be moved and
redesignated as new Sec. 1020.32(b)(6). Additionally, Sec.
1020.32(b)(2)(i) and (b)(2)(ii) will be moved to Sec. 1020.32(b)(4)(i)
as Sec. 1020.32(b)(4)(i)(A) and (b)(4)(i)(B).
New requirements of improved efficiency for systems manufactured
after the effective date of the amendments are proposed in Sec.
1020.32(b)(4)(ii) for systems with inherently circular image receptors.
Section 1020.32(b)(5) would contain the field limitation requirements
for systems with inherently rectangular image receptors. The
requirements proposed for systems with rectangular image receptors are
the same as those currently applicable to radiographic systems provided
with positive beam limitation or to spot-film devices that utilize
rectangular image receptors. As such, the proposed tolerances for x-ray
field limitation are considered technically feasible.
A reduction in unnecessary patient exposure is the basis for all of
the x-ray field limitation and alignment requirements in the
performance standard. For example, any radiation falling outside the
visible area of the image receptor provides no useful diagnostic or
visualization information and, therefore, represents unnecessary
patient exposure. Once it is recognized that restricting the size of
the x-ray field provides an effective control of unnecessary radiation
exposure, the question shifts to what is the tolerance technically
achievable by the manufacturer for the matching of the x-ray field and
the visible area of the image receptor.
The current performance standard (Sec. 1020.32(b)(2)(i)), states
``neither the length nor the width of the x-ray field in the plane of
the image receptor shall exceed that of the visible area of the image
receptor by more than 3 percent of the SID. The sum of the excess
length and the excess width shall be no greater than 4 percent of the
SID.'' These requirements result in worst-case values of geometrical
efficiency enumerated in table 1 of this document for what are typical
geometrical and operating conditions on fluoroscopic systems.
Geometrical efficiency is defined as the ratio of the visible area
divided by the area of the x-ray field. It should be noted that the
requirements in the existing IEC international standard with respect to
x-ray field limitation are more stringent than in the performance
standard (Ref. 4). When the x-ray field is rectangular and the visible
area is circular, the IEC standard requires that the length and width
of the x-ray field be less than the diameter of the maximum visible
area of the image intensifier. Thus, if the x-ray field is centered on
the visible area of the image intensifier, the x-ray field would exceed
the visible area of the image intensifier only in the corners of a
rectangular x-ray field, unlike what could result from following the
current performance standard.
Table 1.--Worst-Case Geometrical Efficiency in Percentage for a
Fluoroscopic System\1\
------------------------------------------------------------------------
Visible Area (circular, X-Ray Field (worst
cm\2\) case, square, cm\2\) Efficiency (%)
------------------------------------------------------------------------
113 196 57
------------------------------------------------------------------------
177 289 61
------------------------------------------------------------------------
415 625 66
------------------------------------------------------------------------
707 1,024 69
------------------------------------------------------------------------
\1\ Worst-Case Geometrical Efficiency in Percentage for a Fluoroscopic
System With a Source-Image Receptor Distance (SID) of 100 cm, a Square
X-Ray Field Size at the Limits Allowed by Sec. 1020.32(b)(2)(i), and
Image Intensifiers With 12-, 15-, 23-, and 30-cm Diameter Visible
Areas.
As can be seen from table 1 above, the current performance standard
allows the possibility of relatively low geometrical efficiency,
particularly in modes of operation corresponding to small visible areas
on the image intensifier. It should be noted that many
fluoroscopically-guided interventional procedures involve the use of
small visible areas on the image intensifier (Ref. 9). These low values
of geometrical efficiency are a direct result of using a square
collimator for the x-ray field when faced with an inherently circular
visible area for the image receptor. The use of a continuously
adjustable, circular collimator and/or circular apertures along with
adjustable rectangular collimation would increase the geometrical
efficiency.
Many currently marketed x-ray systems suitable for
fluoroscopically-guided interventional procedures provide continuously
adjustable, circular collimators as a basic and/or optional capability
(Ref. 10). Thus, a continuously adjustable, circular collimator is
technically feasible, albeit at some additional cost to the user
community. Fluoroscopic x-ray systems with this feature can provide a
substantial increase in geometrical efficiency that is important for
all types of radiological procedures but particularly important for
interventional procedures resulting in high skin exposure.
It is for these reasons that FDA proposes to require geometrical
efficiencies of 80 percent or more for all fluoroscopic x-ray systems.
When the visible area of the image receptor is
[[Page 76062]]
greater than 34 cm in any direction, a geometrical efficiency of 80
percent is no longer sufficiently stringent. FDA proposes to change the
requirement to a sizing tolerance at that point (i.e., the x-ray field
measured along the direction of greatest misalignment with the visible
area of the image receptor shall not extend beyond the visible area of
the image receptor by more than 2 cm). This oversizing tolerance will
ensure geometrical efficiencies of better than 80 percent for large
image receptors. In those unusual cases where the x-ray field is not
uniformly intense over its cross-section, the proposed field limitation
and alignment requirement provides for measurement of efficiency in
terms of air kerma integrated over the x-ray field incident on the
visible area of the image receptor (Ref. 11).
The intent is to promote the incorporation of continuously
adjustable, circular collimators into all types of fluoroscopic x-ray
systems with circular image receptors. FDA acknowledges that the new
requirements could be met through the use of less complex, currently
available, rectangular collimation and underframing. For example, the
amount of underframing (defined as the difference in the width of the
x-ray field versus the diameter of the visible area) of a rectangular
x-ray field needed to meet the new requirements is enumerated in table
2 of this document for the same geometrical and operating conditions of
fluoroscopic systems described in table 1 of this document. The agency
is soliciting comments on the ramifications of this amount of
underframing. These proposed requirements for increased x-ray
utilization efficiency would appear in proposed Sec. 1020.32(b)(4)(ii)
for systems manufactured after the effective date of the amendments.
Table 2.--Underframing of a Rectangular X-Ray Field\1\
------------------------------------------------------------------------
X-Ray Field Width
Visible Area Diameter (cm) (cm) Underframing (cm)
------------------------------------------------------------------------
12 11.9 -0.1
------------------------------------------------------------------------
15 14.9 -0.1
------------------------------------------------------------------------
23 22.8 -0.2
------------------------------------------------------------------------
30 29.7 -0.3
------------------------------------------------------------------------
\1\ Amount of Underframing of a Rectangular X-Ray Field Needed to Meet
the New Field Limitation Requirements for a Fluoroscopic System With
an SID of 100 cm and Image Intensifiers With 12-, 15-, 23-, and 30-cm
Diameter Visible Areas.
Although the field limitation requirements for fluoroscopic
equipment in the performance standard are predicated on the presence of
an x-ray image intensifier, the requirements are also appropriate for
newer imaging systems that do not use an x-ray image intensifier. As
mentioned previously, the newer imaging systems may incorporate an
image receptor consisting of an absorbing material backed by an array
of solid state transducers that intercepts x-ray photons and converts
the photon energy into a modulated electrical signal with eventual
analog-to-digital conversion. These image receptors are inherently
rectangular. As is the case for image intensifier based systems,
magnification modes are available through the use of a ``digital zoom''
where only a selected portion of the digital array is visible to the
operator. FDA is proposing to apply the current requirements of the
standard for x-ray field limitation that are used for spot-film devices
or radiographic systems equipped with positive beam limitation, and
which also use rectangular fields, to this new type of image receptor.
These requirements result in worst-case values of geometrical
efficiency (defined as the square visible area divided by the area of a
square x-ray field) enumerated in table 3 of this document for what are
typical geometrical and operating conditions of fluoroscopic systems.
Table 3.--Worst-Case Geometrical Efficiency in Percentage for a
Fluoroscopic System\1\
------------------------------------------------------------------------
Visible Area Diameter X-Ray Field (square,
(square, cm\2\) cm\2\) Efficiency (%)
------------------------------------------------------------------------
144 196 73
------------------------------------------------------------------------
225 289 78
------------------------------------------------------------------------
529 625 85
------------------------------------------------------------------------
900 1,024 88
------------------------------------------------------------------------
\1\ Worst-Case Geometrical Efficiency in Percentage for a Fluoroscopic
System With an SID of 100 cm, a Square X-Ray Field Size at the Limits
Allowed by Sec. 1020.32(b)(2)(i), and Solid-State X-Ray Images with
12 cm x 12 cm, 15 cm x 15 cm, 23 cm x 23 cm, and 30 cm x 30 cm Visible
Areas.
As can be seen from table 3 above, the current standard provides
relatively high geometrical efficiency. In this case, the high values
of geometrical efficiency are a direct result of using a rectangular
collimator for the x-ray field when faced with an inherently
rectangular visible area for the image receptor. Proposed Sec.
1020.32(b)(5) would explicitly state the field limitation requirements
for systems with inherently rectangular image receptors.
G. Revisions and Change in the Limits to Maximum Air Kerma Rate (Sec.
1020.32(d) and (e))
In Sec. 1020.32, FDA proposes to revise and reorganize Sec.
1020.32(d) and (e) to clarify and simplify the requirements on maximum
AKR for fluoroscopic x-ray systems. In Sec. 1020.32(d), FDA proposes
to incorporate all of the requirements for AKR limits regardless of the
date of manufacture of the x-ray system. The revised paragraph would
also incorporate the new quantity kerma and the corresponding limits on
entrance
[[Page 76063]]
AKRs. FDA proposes to move the current requirements of Sec. 1020.32(e)
that are applicable to equipment manufactured on or after May 19, 1995,
to the revised Sec. 1020.32(d). This would consolidate all of the
requirements for limits on the maximum AKR in a single section (i.e.,
revised Sec. 1020.32(d)). Section 1020.32(e) would be reserved.
The requirements applicable to fluoroscopic systems manufactured
before May 19, 1995, currently contained in Sec. 1020.32(d)(1) through
(d)(3), would be contained in revised Sec. 1020.32(d)(1). No change in
the limit on maximum AKR for previously manufactured fluoroscopic
systems is introduced by the reorganization and simplification of
current Sec. 1020.32(d). This simplification is obtained by describing
the exceptions to the maximum AKR only one time in proposed Sec.
1020.32(d)(1)(v) rather than three times as in current Sec.
1020.32(d)(1) through (d)(3).
Proposed Sec. 1020.32(d)(1) also includes Sec. 1020.32(d)(1)(iv)
that makes explicit the fact that systems manufactured before May 19,
1995, may be modified to comply with new requirements contained in
proposed Sec. 1020.32(d)(2). The rationale for this addition is
described in section II.M of this document.
Proposed Sec. 1020.32(d)(2) would include the requirements
applicable to fluoroscopic systems manufactured on or after May 19,
1995. Section 1020.32(d)(2)(i) would contain the language currently in
Sec. 1020.32(e)(1) that requires systems with the capability for AKR
greater than 44 mGy/min to be provided with automatic exposure rate
control.
Section 1020.32(d)(2)(ii) would contain the requirements of current
Sec. 1020.32(e)(2) that became effective on May 19, 1995, and
establish an upper limit on the AKR during high-level control mode of
operation. Section 1020.32(d)(2)(iii) would incorporate the exceptions
to the maximum AKR limit given in Sec. 1020.32(d)(2)(ii). Section
1020.32(d)(2)(ii)(A) would contain the exception currently found in
Sec. 1020.32(e)(2)(i) that addresses the recording of images using a
pulsed mode applicable to equipment manufactured prior to the effective
date of these amendments. For equipment manufactured after the
effective date of these amendments, Sec. 1020.32(d)(2)(ii)(B) would
add an additional new exception described below in section II.H of this
document. Finally, the exception currently found in Sec.
1020.32(e)(2)(ii) addressing high-level control mode of operation would
be moved to Sec. 1020.32(d)(2)(ii)(C).
The conditions under which compliance is determined are currently
found in Sec. 1020.32(d)(4) and (e)(3). These conditions would be
moved to Sec. 1020.32(d)(3). Section 1020.32(d)(3)(vi) would be added
to specifically address the measurement conditions for systems with
SIDs less than 45 cm. For these systems, FDA is proposing that
compliance be determined by measurement at the minimum SSD.
The exemption for radiation therapy simulation systems currently
found in Sec. 1020.32(d)(5) and (e)(4) would be incorporated into a
proposed revision of Sec. 1020.32(d)(4).
H. New Modes of Image Recording
New requirements would be established in a Sec.
1020.32(d)(2)(iii)(B) to further limit the conditions under which the
limit on the maximum AKR rate would not apply. In May 1994, the agency
amended the requirements in the standard pertaining to the limit on
entrance exposure rate (EER) during fluoroscopy. (For convenience in
discussing the current standard and proposed changes, reference will be
made to the limits on EER rather than to entrance AKR which will be the
quantity used in the amended standard.)
These 1994 amendments prescribed an exception to the limit on EER
during the recording of images ``from an x-ray image intensifier tube
using photographic film or a video camera when the x-ray source is
operated in a pulsed mode.'' (Pulsed mode is defined as operation of
the x-ray system such that the x-ray tube current is pulsed by the x-
ray control to produce one or more exposure intervals of duration less
than one-half second.) These amendments also prescribed a limit on EER
of 20 R/min when an optional high-level control was activated during
fluoroscopy.
The basic premise of these amendments was to provide for a set of
limits on the maximum EER during fluoroscopy, and for an exception
during radiographic modes of operation such as cine-radiography. The
defining terms for determining whether the equipment was in fluoroscopy
versus radiography mode of operation were ``recording of images'' and
``pulsed mode.'' In retrospect, these terms were not explicit enough
for making a determination of the mode of operation. For example, the
current wording would allow adding a recording device such as a video
tape recorder to the imaging chain in a pulsed mode of operation. This
would, thereby, circumvent the intent of the regulation and allow the
limit on maximum EER during fluoroscopy to be exceeded, even though the
recorded images are never used in the radiological examination and are
used only for archiving purposes, if used at all.
As mentioned in the earlier discussion on new types of image
receptors, FDA is proposing new definitions for fluoroscopy and
radiography. These definitions are needed to make a clearer distinction
between fluoroscopy and radiography, regardless of the type of image
receptor being used. A key element in the new definitions is that
radiographic images recorded from the fluoroscopic image receptor must
be available for viewing after the acquisition of the images and during
or after the procedure, whereas fluoroscopic images are viewed in real
time, or near-real time during the procedure. Thus, the definitions of
the two modes of operation, i.e., radiography and fluoroscopy, are tied
to the intended use, and not to an arbitrary interval of time, as under
the current ``pulsed mode'' definition.
In addition to the proposed new definitions, FDA proposes to change
the description of the conditions under which exceptions to the limit
on maximum AKR are allowed. Section 1020.32(d)(2(iii) would contain two
exemptions. The exemption currently in Sec. 1020.32(e)(2)(i) would be
moved to Sec. 1020.32(d)(2)(iii)(A) and would apply to fluoroscopic
systems manufactured on or after May 19, 1995, but before the effective
date of the proposed amendment. A new exception would be added in Sec.
1020.32(d)(2)(iii)(B). This exception would recognize that image
receptors other than x-ray image intensifiers tubes are now used in
fluoroscopy and would remove the reference to operation in a pulsed
mode. Instead, the exception to the limit on maximum AKR would apply to
any recording of images from the fluoroscopic image receptor except
when the recording of images is accomplished using a video tape
recorder or a video disk recorder. This would prevent the simple
addition of an analog image-recording device to the fluoroscopic system
as a means to overcome the limit on maximum AKR during normal
fluoroscopy.
As discussed in the preamble of the proposed 1993 amendments (58 FR
26407, May 3, 1993), the agency is still interested in receiving
information on any clinical situations that could require higher AKR
than currently permitted. Such situations have been suggested to arise
due to the necessity of momentarily viewing the patient or the state of
a device in a patient as best as can be done or with the highest image
quality obtainable during fluoroscopy
[[Page 76064]]
mode of operation. Some anecdotal evidence seems to argue for an
increase in the EER above the current 20 R/min limit under high-level
control. The 1994 change in the regulations underwent an extensive
review and comment period. The consensus of that review, although not
unanimous at the time of issuance of the regulations, was that 20 R/min
would be sufficiently high for most clinical fluoroscopy situations.
The agency was and is still sensitive to the concern that the limits on
EER may in some cases compromise the clinical utility of the
fluoroscopic equipment.
Because of these concerns regarding the appropriate upper limit
AKR, FDA is encouraging further comment on the topic of limits on AKR
under normal and high-level fluoroscopy modes. For example, some
members of the radiological community have proposed that fluoroscopic
equipment allow a momentary viewing of the state of an intervention at
an increased but unspecified AKR. This momentary view would have a
maximum duration of 10 to 15 seconds. This proposal was accompanied
with the comment that if physicians are not allowed to use such a mode,
they will continue the practice of using cineradiography bursts at high
AKRs to accomplish the clinical task.
I. Entrance Air Kerma Rate at the Fluoroscopic Image Receptor
Comments received by the agency suggest that an alternative
approach in place of or in addition to limits on AKR during fluoroscopy
would be more useful and effective in limiting unnecessary radiation
and assuring optimum system performance. The suggestion is that the
limits on AKR to the patient (represented by a measurement made
according to the compliance geometry described in current Sec.
1020.32(e)(3)) be replaced by limits on the entrance AKR at the input
surface of the image receptor (EAKIR). Different EAKIR limits could be
established for different modes of fluoroscopic imaging, depending on
the image performance required for the clinical task.
There is a precedent for this approach in other consensus documents
such as the NCRP Report No. 99 and NCRP Report No. 102 (Refs. 12 and
13). For example, the NCRP Report No. 99 states that during fluoroscopy
``typical image intensifier entrance exposure should be in the range of
13 to 52 nC/kg/image (50 to 200 microR/image) depending on image
intensifier size * * *.'' (Note that, in the opinion of FDA, there is
an error in the NCRP Report No. 99: these numbers reflect exposure per
second, not exposure per image.) In the same manner, the NCRP Report
No. 102 provides a table with ``air kerma rate values to produce
acceptable fluoroscopy images'' and ``air kerma to produce static
images equivalent to that produced by a par speed screen-film system.''
FDA invites comments on the feasibility and desirability of this
approach to limit unnecessary radiation from fluoroscopic systems.
J. Requirement for Minimum Source-Skin Distance for Small C-Arm
Fluoroscopic Systems (Sec. 1020.32(g))
FDA proposes in Sec. 1020.32(g) to add Sec. 1020.32(g)(2) to
establish a minimum source-skin distance (MSSD) for ``C-arm'' type x-
ray systems having source-to-image-receptor distances of 45 cm or less
and intended for imaging extremities. This amendment would incorporate
into the performance standard the content of variances from the
performance standard granted according to Sec. 1010.4.
FDA has granted variances from the requirement set out in
Sec. 1020.32(g) for a limit on the MSSD for fluoroscopic x-ray systems
that were designed as small portable C-arm systems. These are
fluoroscopic systems that were originally designed to be hand-held and
were used at sporting events for a quick examination/diagnosis of
orthopedic injuries. In fact, some of the early systems used a
radioisotope instead of an x-ray tube as the source of the radiation
and were, therefore, outside the purview of FDA under the RCHSA
(although they are regulated as medical devices). Over time,
manufacturers of these devices enlarged the distance or opening between
the x-ray source and the image receptor to allow examination of larger
extremities. The argument was that some athletes had larger extremities
and a larger opening was needed to permit the use of the systems on
them. The systems were marketed under a variance from Sec. 1020.32(g)
and were labeled for extremity use only. As the size of the opening on
systems for which variances have been requested has increased from
about 20 cm to 35 cm, and manufacturers have increased the radiation
output of these systems, the agency has become concerned about the loss
of the skin-dose sparing properties of the MSSD requirement. In
addition, because a variance is granted for a finite time period,
renewal of the variances and the reviewing of new conditions for use
present resource implications for FDA and the manufacturers.
The justification for a variance from Sec. 1020.32(g) used by many
manufacturers of these small C-arm systems is geometrical scaling.
Manufacturers have stated in their variance applications that the MSSD
is proportional to the source-image receptor distance in comparison to
full-sized C-arm systems. Although extremities can be considered to
scale geometrically in a similar manner compared to the trunk or large
body parts, other body parts do not scale in such a manner as to
maintain a similar skin dose. For the source-image receptor distances
used in these systems, evaluation of this geometrical relationship
shows that the factor, by which the entrance AKR to the body part
increases over that for thinner parts, increases significantly as the
thickness of the body part being imaged reaches over 15 or 16 cm. This
increase reaches a factor of two for a thickness of 26 cm and increases
rapidly for thicker parts. In their original configuration, these
devices had a very small opening and could not accommodate anything
other than a limb. The latest configurations can easily accommodate the
whole body of a neonate or a pediatric patient.
At some point, these systems no longer represent small C-arms for
extremity use alone but are simply slightly smaller versions of
conventional C-arms for whole-body, general-purpose examinations. If
the system can be used for whole-body examination purposes, it should
meet the minimum radiation safety standards applicable to conventional
C-arm systems. Through the variance petition process, FDA has limited
the small C-arm systems to extremity use only.
To incorporate the protection provided by the conditions imposed by
the variances and to incorporate this requirement in the performance
standard, FDA proposes to limit the source-skin distance to not less
than 19 cm for fluoroscopic systems having source-image receptor
distances of 45 cm or less. Provision would be allowed for systems
designed for specific surgical applications to be operated with a
source-skin distance of not less than 10 cm. Systems subject to this
requirement would be required to be labeled for use for imaging
extremities only. Manufacturers would be required to include
appropriate precautions in the information provided to users under
Sec. 1020.30(h).
K. Requirements for Display of Fluoroscopic Irradiation Time, Air Kerma
Rate, and Cumulative Air Kerma (Sec. 1020.32(h) and Proposed (k))
FDA is proposing that newly manufactured fluoroscopic systems
display directly to the fluoroscopist information related to three
[[Page 76065]]
fundamental aspects of patient irradiation--the duration, rate, and
amount of x-ray emissions. Generally, fluoroscopic systems do not
currently provide such information at all. Irradiation time, AKR, and
cumulative air kerma are basic radiological variables important for
medical radiation protection. Their values may be applied to the
process of optimization (i.e., obtaining radiological images with the
least amount of radiation required), to the assessment of radiation
detriment as a factor affecting patient-outcome efficacy, and to the
development of reference levels representative of normal clinical
practice. Optimization, efficacy, and reference levels currently
comprise a conceptual vanguard of radiation protection in medicine at
the international level (Refs. 14 to 17). When monitored in the clinic,
irradiation time, AKR, and cumulative air kerma may be used to indicate
risk of acute skin injury arising from potentially prolonged
irradiation associated with some interventional procedures (Refs. 18 to
20). Values displayed directly to practitioners as an examination or
procedure progresses can feed back to them indices of radiation burden,
and practitioners can respond promptly by adjusting protocols and
techniques to minimize dose to patients and practitioners as
practitioners optimize radiation levels necessary for medical imaging.
Moreover, for fluoroscopy and radiography in general, knowledge of
irradiation levels at patient skin entrance is an essential starting
place for evaluation of absorbed dose to internal tissues (Refs. 9 and
21). Such doses are stochastically linked to cancer morbidity,
mortality, and to genetically transmissible defects (Refs. 14 and 22).
Estimates of cumulative doses absorbed in tissues foster risk
communication between medical staff and patients and, when tracked over
time, are effective indicators of practice consistency, variability, or
anomaly in the quality assurance activities associated with assuring
the safety of clinical procedures.
The need for displays of irradiation variables was recognized at
the 1992 national workshop on safety issues in fluoroscopy organized by
the ACR and FDA (Ref. 8). In October 1995, the need was also recognized
internationally by the workshop on efficacy and radiation safety in
interventional radiology, sponsored jointly by the World Health
Organization and the Institute of Radiation Hygiene, Radiation
Protection Ministry, Federal Republic of Germany (Ref. 23). Recently,
requirements for displays of irradiation parameters have been
incorporated into an international standard for x-ray systems for
interventional radiology (Ref. 24). With the advent of commercially
available and relatively inexpensive means to measure and display real-
time AKR and cumulative air kerma produced by fluoroscopic systems
(Ref. 25), it is feasible as well as desirable to require that this
information be directly observable by fluoroscopists at their working
positions.
The proposed display requirements would apply to all types of newly
manufactured fluoroscopic equipment (i.e., from systems found in
cardiac catheterization suites, to equipment used for upper
gastrointestinal fluoroscopy, to ``mini'' C-arms, and also to each
fluoroscopic x-ray tube as part of any system). FDA invites comments
about whether these requirements would be suitable to all types, or to
a limited set of fluoroscopic equipment, namely, to stationary C-arm
fluoroscopes that are typically used in interventional procedures.
1. Fluoroscopic Irradiation Time, Display, and Signal
Fluoroscopic irradiation time is profoundly tied to patient dose in
a complex way that involves many other factors (e.g., see Ref. 26). FDA
believes it advantageous to require that cumulative irradiation-time
values be treated in their own right, in addition to the other
variables cited in the proposed Sec. 1020.32(k), as radiological
parameters whose control would facilitate radiation-protection
optimization. Physician members of TEPRSSC pointed out at its September
1998 meeting that irradiation time is the single fundamental variable
over which a physician using fluoroscopy has the most direct and
easiest control through activating or deactivating x-ray production,
typically by means of a pedal switch (Ref. 27).
FDA proposes to add Sec. 1020.32(h)(2) to the regulations to
change the current fluoroscopic timer requirement in two ways. First,
Sec. 1020.32(h)(2)(i) would require that the values of the cumulative
irradiation times associated with each of the fluoroscopic tubes of a
system used in an examination or procedure be displayed to the
fluoroscopist at his or her working position. The displayed values
would be indicated from the beginning, throughout, and after an
examination ends, available until the cumulative irradiation timer is
reset to zero prior to a new examination. Second, Sec.
1020.32(h)(2)(ii) would require an audible signal cycle different from
that of current equipment for each x-ray tube used during an
examination or procedure. Contrary to the current provision that allows
the timing device to be preset to any interval up until a maximum
cumulative irradiation time of 5 minutes, FDA proposes that a signal
audible to the fluoroscopist sound at each fixed interval of 5 minutes
of irradiation time. Also contrary to the current requirement, instead
of sounding until reset, the audible signal would sound (while x-rays
are produced) for a minimum of only 1 second, after which the signal
could stop until a subsequent 5 minutes of irradiation elapses. The
audible signal would not affect the production of x-rays, the display
of cumulative irradiation-time values required by Sec.
1020.32(h)(2)(i), or any of the other displays proposed in Sec.
1020.32(k).
Considering advice offered at the 1998 TEPRSSC meeting (Ref. 27),
FDA now believes that a fixed, standard (5 minute) period for an alert
signal would avoid potential confusion that could ensue with a
fluoroscopic timer that is variably preset. For example, such confusion
could arise in a busy clinical facility with many different users,
where fluoroscopists might not be aware of the need to readjust alert
intervals that had been changed previously by other fluoroscopists to
accommodate the individual protocol requirements associated with
particular patient examinations. Furthermore, FDA believes that an
audible signal of short duration would be a more effective and useful
alert than a signal that sounds continuously, requires a reset, and
therefore, could pose a distraction to users. FDA seeks comments about
the audible signal cycle in proposed Sec. 1020.32(h)(2)(ii),
particularly in comparison to the suggested alternative below that is
not currently in the proposal.
As an alternative approach, the selection of the time period until
the alarm sounds could be at the discretion of the fluoroscopist. The
timer could be preset to any period (less than, equal to, or greater
than 5 minutes), or preset even to not sound at all. Under this
approach, before an examination or procedure, the fluoroscopist could
select a period beyond which an audible signal would sound until the
timer could be reset (or else sound briefly then remain silent until
the preset fluoroscopic period elapses again). Presuming clinicians
maintain personal cognizance of fluoroscopic timer options and
adaptability, such alternatives would offer them flexibility and
opportunity to apply standard features of equipment operation to their
[[Page 76066]]
own individual clinical protocols and practices.
FDA also seeks comment on whether the display of the cumulative
irradiation time should be visible to the fluoroscopist at his or her
working position or whether it is sufficient to display the cumulative
time at the control console. It has been suggested that this display
should be available to the fluoroscopist to permit constant monitoring
by the fluoroscopist. Other opinions are that such a display at the
working position would only add confusion to an already complex visual
environment, and display of the cumulative irradiation time at the x-
ray control would make the information available in any case. Display
at the fluoroscopist's working position may be slightly more complex or
costly than display at the x-ray control.
2. Displays of Air Kerma Rate and Cumulative Air Kerma
FDA believes that a requirement for displays of AKR and cumulative
air kerma values would significantly advance the optimization of
radiation safety, in consideration of recent developments in clinical
practice and technology (Refs. 23, 25, and 26), an evolving consensus
for a radiation-protection framework (Refs. 14 to 17), and specific
guidance (Refs. 18 to 20). Air kerma and AKR are fundamental
radiological quantities of the amount and rate of charged-particle
kinetic energy liberated per mass of air traversed by incident x-rays
(Ref. 1). For this reason, FDA proposes to add Sec. 1020.32(k) to
require that all new fluoroscopic systems be capable of displaying
real-time values of the AKR and cumulative air kerma delivered by each
x-ray tube at reference locations representative of x-ray beam entry to
the patient skin surface. These displays would be directly discernible
at the fluoroscopist's working position, and the displayed values would
deviate by no more than +/-25 percent from actual values. To elucidate
these requirements and those of the other proposed amendments, the
definitions of the terms ``fluoroscopy,'' ``mode of operation,'' ``and
radiography'' are proposed in Sec. 1020.30(b). The utility of the
display requirements could be broadly leveraged among practitioners in
a variety of clinical settings through familiarization with relatively
standardized display formats. Such standardization is proposed in Sec.
1020.32(k)(1) through (k)(7), where the particular requirements
proposed conform generally to those of the recently published IEC
standard (Ref. 24).
During fluoroscopy or while recording images during a fluoroscopic
procedure, the displayed value of the AKR would represent in real time
the magnitude of air kerma per unit time being delivered at any
geometrical point within a specified reference locus. The displayed
value of the cumulative air kerma would represent a sum of two parts:
(1) The fluoroscopic AKR integrated over an interval until update, and
(2) all contributions to the air kerma (at any point in the same
reference locus) from radiography occurring in that interval. The
cumulative air kerma would be updated throughout the examination or
procedure, and the integration interval would be the time between the
start of an examination or procedure and the end of the most recent
episode of either fluoroscopy or radiography during that same
examination or procedure.
For each x-ray tube used during fluoroscopy or during recording of
fluoroscopy, the value of the AKR will be displayed. After the
cessation of fluoroscopy, the cumulative air kerma will be displayed
and will remain displayed until the resumption of fluoroscopy or a
radiographic mode is activated or the display is reset for a new
patient or procedure. Thus, the cumulative air kerma will be displayed
after x-ray production ceases from either fluoroscopy or radiography.
Values of the AKR are displayed at times other than those for the
cumulative air kerma in order to underscore the distinction between
these two variables and also to reduce the potential for overwhelming
the fluoroscopist with too much information presented at once. At any
particular moment during an examination or procedure, only values of
the irradiation time and AKR (or cumulative air kerma) would be on
display for each tube used. If, for example, a biplane fluoroscopic
system were used in some cardiac catheterization procedure, two
separate sets of values--one set for each of the x-ray tubes of the
biplane--would be displayed. Under such circumstances of multiple
presentations of related information, it is important that the values
displayed be distinguishable enough from each other to be easily
recognized and associated with the different radiological variables
they represent. For this reason, FDA proposes in Sec. 1020.32(h)(2)(i)
and (k)(3) to require that the units of measurement be displayed as
well as the values per se. FDA also proposes in Sec. 1020.32(k)(1) and
(k)(2) to require that the measurement units mGy/min and mGy be
displayed respectively alongside the values for AKR and cumulative air
kerma. These values would serve as a labeling distinction to preclude
potential confusion of the quantities.
As measures of fundamental radiological quantities, the displayed
values of AKR and cumulative air kerma would refer to free-in-air
irradiation conditions (i.e., their evaluations would be made minus any
contributions of scatter radiation, particularly contributions
backscattered from a patient (or from a measurement phantom)). Also,
the displayed values would refer to irradiation conditions at a
reference location (i.e., at any geometrical point contained within a
specific reference locus defined according to the type of fluoroscopic
system). Each reference location is intended to represent, at least
nominally, a place of x-ray beam entry to the patient skin. For
fluoroscopes with the x-ray source below or above the table, or of the
lateral type, Sec. 1020.32(k)(5)(i) would have skin-entrance reference
locations correspond identically and respectively to those specified in
Sec. 1020.32(d)(3)(i), (d)(3)(ii), or (d)(3)(v). These locations
define the geometry for measuring compliance with the regulatory maxima
of the AKR.
For C-arm type fluoroscopes, however, in many cases the locations
proposed for measuring compliance with the regulatory maxima of the
AKR, given in Sec. 1020.32(d)(3)(iii) and (d)(3)(iv), would not
suitably represent where the x-ray field enters the patient skin. This
is especially true for oblique angulations and extended distances
between the x-ray source and image receptor. Therefore, in Sec.
1020.32(k)(5)(ii), for C-arm systems, FDA is proposing a skin-entrance
reference location for display quantities that is different from the
location for measuring compliance with regulatory AKR limits. For
evaluation of displayed values, the skin-entrance reference location
would be either 15 cm from the isocenter toward the x-ray source along
the beam axis (irrespective of angulation) or, alternatively, along the
beam axis at a point deemed by the manufacturer to represent the
intersection of the x-ray beam and the entrance surface of the patient
skin. A definition of ``isocenter'' is proposed in Sec. 1020.30(b).
Proposed Sec. 1020.32(k)(5)(ii) would allow manufacturers to choose
either the 15-cm locus or specify the alternative. The alternative
locus would offer manufacturers flexibility to provide systems that
could evaluate AKR and cumulative air kerma in closer proximity to
actual places of x-ray beam entry to patients than could systems with
reference skin entrance defined
[[Page 76067]]
generically at a 15-cm locus from the isocenter. An alternative skin-
entrance reference location may be particularly appropriate for mini C-
arm fluoroscopes (i.e., those with SID less than 45 cm, for which the
15-cm locus from the isocenter may be physically unrealizable). In any
case, new paragraphs Sec. 1020.30(h)(6)(iii) and (h)(6)(iv) would
require that manufacturers identify to the user the spatial coordinates
of the irradiation location to which displayed values refer and also
provide a rationale justifying any reference location identified as an
alternative to the 15-cm locus.
In patient examinations or procedures with C-arm systems, one
possible result of having reference locations of x-ray beam skin-entry
different from the measurement sites for AKR compliance is that
displayed values could actually exceed the regulatory maxima even
though the system is fully compliant. Such a situation could arise for
some irradiation geometry when the reference skin-entrance location is
closer to the x-ray source than is the site for measuring compliance.
Displayed values of the AKR and cumulative air kerma are intended to
inform the fluoroscopist of radiation burden to the patient.
Conversely, the AKR regulatory maxima, practicably measured 30 cm from
the imaging-assembly input, according to Sec. 1020.32(d)(3)(iii) or at
the minimum SSD according to Sec. 1020.32(d)(3)(iv), are intended to
impose upper limits on radiation output that are compatible with the
levels needed by the imaging chain for adequate fluoroscopic
visualization.
Reset of the displays to zero would occur between sessions with
successive patients. Before reset, a final value of the cumulative air
kerma may serve to reinforce an association between the culmination of
a radiological examination or procedure and the radiation burden
incurred by the patient. FDA believes that the availability of this
value would greatly facilitate the implementation of previously
published recommendations (Refs. 18 to 20) on recording information in
the patient's medical record to identify the potential for serious x-
ray-induced skin injuries in order to avoid them.
L. ``Last-Image Hold'' Feature on Fluoroscopic Systems (Proposed Sec.
1020.32(j))
FDA proposes to add a paragraph to require that all fluoroscopic x-
ray systems be provided with a means to continuously display the last
image acquired prior to termination of exposure.
The wide availability of electronic methods for the recording and
displaying of video images makes possible the provision of a ``last-
image hold'' or ``freeze-frame'' capability on fluoroscopic x-ray
systems. This feature allows the fluoroscopic x-ray system to
continuously present a static image of the last fluoroscopic scene
captured or presented at termination of the fluoroscopic exposure. This
feature also provides the user with the ability to conveniently view
fluoroscopic images without continuously irradiating the patient.
This feature is especially useful in procedures such as
fluoroscopically-guided needle placement for biopsy or drainage,
catheter or tube placement, and other diagnostic or therapeutic
interventional procedures. Systems provided with this feature reduce
fluoroscopic exposure times while enabling extended examination and
planning during fluoroscopically-guided procedures.
This capability is provided as a basic or optional feature on many
currently marketed fluoroscopic systems. Many individuals have
expressed the opinion that because of the radiation dose reduction
afforded by such a feature, it should be provided on all new
fluoroscopic systems. Such a recommendation was strongly endorsed at
the workshop on fluoroscopy in 1992 (Ref. 8). In addition, a
requirement for this capability is included in the recently published
IEC standard for the safety of x-ray equipment for interventional
radiology (Ref. 24). Establishing this requirement would assure that
all new fluoroscopic systems have this patient radiation dose reduction
feature and that it is available when its use is appropriate. Without
such a requirement, some systems may for economic reasons continue to
be purchased without this feature, thereby denying dose reduction
benefits to patients.
Proposed Sec. 1020.32(j) would permit the displayed image to be
obtained from the last or a combination of the last few fluoroscopic
video frames obtained just prior to termination of fluoroscopic
exposure or by an alternative implementation via a radiographic
exposure automatically produced at termination of the fluoroscopic
exposure. Comments are solicited as to whether these approaches to
implementation of last image-hold are appropriate and needed.
M. Modification of Previously Manufactured and Certified Equipment
FDA proposes to add language to Sec. 1020.32(d)(1)(iv) and (h) to
make explicit the opportunity under Sec. 1020.30(q) for modifications
to be made to existing certified x-ray systems. Modifications are
currently permitted as long as the modification does not result in a
failure to comply with the requirements of the performance standard.
Changes in performance resulting from amendments to the performance
standard often result in enhanced radiation safety or features not
available on previously manufactured and certified systems.
The existing performance standard requires manufacturers to certify
that their products meet the applicable performance requirements in
effect at the time of manufacture. Therefore, amendments to the
performance standard are generally not retroactive and effective dates
implementing the standard are specified in the regulations. Usually, a
1-year effective date is provided in order to allow manufacturers time
to adjust manufacturing and assembly of their products under the new or
amended regulations. Indeed, it would be unreasonable to require the
manufacturer to retrofit or to remanufacture previously produced
products because of a change in the standard for equipment that could
have a useful life of 20 or more years.
In particular, the performance requirements regarding maximum
exposure rate limits (proposed to become maximum AKR limits),
established in 1994 (59 FR 26402), and the proposed requirements in
Sec. 1020.32(h) for fluoroscopic timers are requirements or
performance features that users of older fluoroscopic equipment may
wish to implement on their systems. The earlier amendment in 1994 and
the current proposal apply to new equipment manufactured after the
effective date of the amendment. The language proposed for inclusion in
Sec. 1020.32(d) and (h) would provide a mechanism for users of older
equipment to obtain the performance required under the proposed
amendments. These changes would allow older systems to be modified to
meet the maximum AKR limit and fluoroscopic timer performance that will
be required under the proposed requirements.
The owner of the fluoroscopic system modified under Sec.
1020.30(q) is responsible for assuring that the modified x-ray system
complies with the applicable requirements of the performance standard
following the modification. The modification to the system may be
accomplished by a third party or by the original equipment
manufacturer. The system owner, however, is responsible for assuring,
[[Page 76068]]
through contract requirements with the party performing the
modification or through testing, that the modified system complies with
the standard following the modification.
N. Modification of Warning Label (Sec. 1020.30(j))
FDA proposes to modify the language of the warning label required
by Sec. 1020.30(j). The current statement warns that safe exposure
factors and operating instructions must be followed. FDA proposes to
modify the warning label statement by adding the phrase ``maintenance
schedules.'' This addition incorporates the suggestion of the TEPRSSC
and further emphasizes the need for diagnostic x-ray systems to be
properly maintained and calibrated. Manufacturers of diagnostic x-ray
systems are required under Sec. 1020.30(h)(1)(ii) to provide a
schedule of the maintenance necessary to keep the equipment in
compliance with the performance standard. The standard places no
requirement on owners or users of diagnostic systems to properly
maintain these systems. However, the revised wording of the warning
label is intended to alert users and facility administrators of the
need to properly maintain the systems.
O. Corrections of Sec. 1020.31(f)(3) and (m)
FDA proposes to correct oversights in Sec. 1020.31(f)(3) and (m)
that occurred when the July 2, 1999, amendment was published. Section
1020.31(f)(3) addresses the x-ray field limitation requirement for
mammographic x-ray systems and Sec. 1020.31(m) addresses the primary
barrier required for mammographic x-ray systems. Prior to September 30,
1999 (the effective date of the final rule), the heading to Sec.
1020.31(m) was ``Transmission limit for image receptor supporting
devices used for mammography.''
When an existing radiation safety performance standard is amended,
the new or modified requirement applies only to products that are
manufactured after the effective date of the amendment. Normally, the
requirement that existed prior to the amendment is retained in the Code
of Federal Regulations (CFR) to provide a record of the requirements of
the standard applicable to products on their date of manufacture. When
the final rule amending Sec. 1020.31(f)(3) and (m) was published on
July 2, 1999, the provisions describing the requirements for equipment
manufactured prior to September were inadvertently omitted. Thus, the
CFR (21 CFR part 1020) has no record of the requirements imposed by
Sec. 1020.31(f)(3) and (m) for equipment manufactured between the
initial effective dates for Sec. 1020.31(f)(3) and (m) and September
30, 1999. To correct this oversight, FDA proposes to reinstate the
provisions describing the requirements that apply to equipment
manufactured prior to September 30, 1999, under the earlier versions of
Sec. 1020.31(f)(3) and (m). This correction will provide a record of
the requirements applicable before September 30, 1999, and close the
gap that exists as a result of the oversight in the publication of the
final rule.
Additionally, further review of this issue revealed that the
original publication of Sec. 1020.31(f)(3) in 1977 (42 FR 44230) did
not indicate an effective date for this paragraph, which was November
1, 1977. FDA proposes to insert the omitted effective date. The
omission was of little consequence because the original requirement
reflected the then current designs of mammographic systems. FDA
proposes to insert the date to provide an accurate record of the
applicable x-ray field limitation requirements as a function of the
date of manufacture of mammographic x-ray systems.
No changes in the previously applicable or current requirements are
proposed or intended by these corrections to Sec. 1020.31(f)(3) and
(m). The corrections are only intended to make explicit the current or
previously applicable requirements that existed on the date of
manufacture.
FDA proposes to revise Sec. 1020.31(f) by adding Sec.
1020.31(f)(3)(i), the requirement applicable to equipment manufactured
on or after November 1, 1977, and before September 30, 1999. The
current requirement, applicable to equipment manufactured after
September 30, 1999, would be Sec. 1020.31(f)(3)(ii). Section
1020.31(f)(3)(iii) would contain the requirement for permanent markings
that are applicable to all equipment manufactured after November 1,
1977.
FDA proposes to amend Sec. 1020.31(m). Section 1020.31(m)(1) would
be revised to contain the requirement applicable to systems
manufactured on or after September 5, 1978, and before September 30,
1999; such requirement was previously omitted. Section 1020.31(m)(2)
would be revised to contain the current requirements applicable to
equipment manufactured after September 30, 1999, in Sec.
1020.31(m)(2)(i), (m)(2)(ii), (m)(2)(iii), and (m)(2)(iv). Section
1020.31(m)(3) would be revised to contain the description of the method
for measuring compliance; such description is common to both Sec.
1020.31(m)(1) and (m)(2). A minor technical clarification is also
proposed in Sec. 1020.31(m)(2)(ii) where the term ``x-ray tube'' found
in current Sec. 1020.31(m)(2) is replaced by the term ``x-ray system''
to reflect the fact that it is the x-ray system, not the x-ray tube,
that controls initiation of x-ray exposure. This change does not change
the intent or effect of the requirement.
P. Corrections to Reflect Changes in Organizational Name, Address, and
Law (Sec. 1020.30(c), (d), and (q))
FDA proposes to amend Sec. 1020.30(c) to reflect the current
organizational title of the Office of Compliance of the Center for
Devices and Radiological Health. FDA also proposes in Sec. 1020.30(d)
to remove the specific address that is subject to change from time to
time. Additionally, FDA proposes to amend paragraph Sec. 1020.30(q) to
reflect the transfer of sections 358(a)(5) and 360B(b) of the PHS Act
to the act by the SMDA.
Q. Removal of Reference to Special Attachments for Mammography
FDA proposes to remove reference to ``special attachments for
mammography'' in Sec. 1020.31(d) and (e). The Mammography Quality
Standards established in part 900 (21 CFR part 900), particularly Sec.
900.12(b)(1), require that only diagnostic x-ray systems designed
specifically for mammography be used to perform mammography in the
United States. Therefore, the use of special attachments intended for
use with general-purpose diagnostic x-ray systems to perform
mammography is inappropriate. No such devices may continue to be used,
and retaining this reference in the standard would imply that such
devices or components were acceptable.
R. Change to the Applicability Statement for Sec. 1020.32
FDA proposes in the applicability statement of Sec. 1020.32 to
remove the reference to ``fluoroscopy'' and replace it with
``fluoroscopic imaging'' and to remove ``recording of images through an
image intensifier tube'' and replace this reference with ``radiographic
imaging when the radiographic images are recorded from the fluoroscopic
image receptor.'' This change is necessary to clarify the applicability
of this section and to incorporate the proposed requirements addressing
the production of radiographic images for the last image hold feature.
S. Republication of Sec. Sec. 1020.30, 1020.31, and 1020.32
Because of the large number of proposed changes in Sec. Sec.
1020.30,
[[Page 76069]]
1020.31, and 1020.32, FDA is republishing these entire sections,
including the proposed amendments, rather than publishing only the
proposed individual changes to these sections. Although some of the
paragraphs in these sections are not changed by this proposal,
republication of the entire sections will result in a more reader-
friendly version when the final regulation is published.
III. Proposed Effective Date
FDA proposes that any final rule based on this proposal become
effective 1 year after the date of publication of the final rule in the
Federal Register.
IV. Environmental Impact
The agency has determined under 21 CFR 25.30(i) and 25.34(c) that
this action is of a type that does not individually or cumulatively
have a significant effect on the human environment. Therefore, neither
an environmental assessment nor an environmental impact statement is
required.
V. Paperwork Reduction Act of 1995
A. Summary
This proposed rule contains information collection provisions that
are subject to review by OMB under the Paperwork Reduction Act of 1995
(PRA) (44 U.S.C. 3501-3502). A description of these provisions is given
in the following paragraphs with an estimate of the annual reporting
and recordkeeping burden. Included in the estimate is the time for
reviewing instructions, searching existing data sources, gathering and
maintaining the data needed, and completing and reviewing each
collection of information.
The information collection burden of the current performance
standard is covered by an existing information collection clearance,
OMB control number 0190-0025. FDA is seeking new information collection
clearance for proposed Sec. Sec. 1020.30(h)(5) and (6), and
1020.32(j)(4).
FDA invites comments on: (1) Whether the proposed collection of
information is necessary for the proper performance of FDA's functions,
including whether the information will have practical utility; (2) the
accuracy of FDA's estimate of the burden of the proposed collection of
information, including the validity of the methodology and assumptions
used; (3) ways to enhance the quality, utility, and clarity of the
information to be collected; and (4) ways to minimize the burden of the
collection of information on respondents, including through the use of
automated collection techniques, when appropriate, and other forms of
information technology.
Performance Standard for Diagnostic X-Ray Systems and their Major
Components (21 CFR 1020.30 and 1020.32 amended)
Description: FDA is proposing to amend the performance standard for
diagnostic x-ray systems by establishing, among other things,
requirements for several new equipment features on all new fluoroscopic
x-ray systems. In the current performance standard, Sec. 1020.30(h)
requires that manufacturers provide to purchasers of x-ray equipment,
and to others upon request, manuals or instruction sheets that contain
technical and safety information. This required information is
necessary for all purchasers (users of the equipment) to have in order
to safely operate the equipment. Section 1020.30(h) currently describes
the information that must be provided.
The proposed rule would add to Sec. 1020.30(h) paragraphs (5) and
(6) describing additional information that would need to be included in
these manuals or instructions. In addition, proposed Sec.
1020.32(j)(4) would specify additional descriptive information to be
included in the user manuals for fluoroscopic x-ray systems required by
Sec. 1020.30(h). This additional information would be descriptions of
features of the x-ray equipment required by the proposed amendments and
information determined to be appropriate and necessary for safe
operation of the equipment.
Description of Respondents: Manufacturers of fluoroscopic x-ray
systems that introduce fluoroscopic x-ray systems into commerce
following the effective date of the proposed amendments. FDA estimates
the burden of this collection of information as follows:
Table 4.--Estimated Average Annual Reporting Burden for the First
Year\1\
------------------------------------------------------------------------
Annual
No. of Frequency Total Hours Total
21 CFR Section Respondents per Annual per Hours
Respondent Responses Response
------------------------------------------------------------------------
1020.30(h)(5) and 20 10 200 180 36,000
(h)(6) and
1020.32(j)(4)
------------------------------------------------------------------------
\1\ There are no capital costs or operating and maintenance costs
associated with this collection of information.
Table 5.--Estimated Average Annual Reporting Burden for Second and
Following Year\1\
------------------------------------------------------------------------
Annual
No. of Frequency Total Hours Total
21 CFR Section Respondents per Annual per Hours
Respondent Responses Response
------------------------------------------------------------------------
1020.30(h)(5) and 20 5 100 180 18,000
(h)(6) and
1020.32(j)(4)
------------------------------------------------------------------------
\1\ There are no capital costs or operating and maintenance costs
associated with this collection of information.
B. Estimate of Burden
As described in the assessment of the cost impact of the proposed
amendment (Ref. 33), it is estimated that there are about 20
manufacturers of fluoroscopic x-ray systems who market in the United
States. Each of these manufacturers is estimated to market about 10
distinct models of fluoroscopic x-ray systems. Immediately following
the effective date of the proposed amendments, for each model of
fluoroscopic x-ray system that manufacturers continue to market, each
manufacturer would have to supplement the user instructions to include
the additional information required by the proposed amendments.
Manufacturers already develop, produce, and provide x-ray system
user manuals or instructions containing the information necessary to
operate the systems, as well as the specific information required to be
provided by the existing standard in current Sec. 1020.30(h).
Therefore, it is assumed that no significant additional capital,
[[Page 76070]]
operating, or maintenance costs will occur to the manufacturers in
connection with the provision of the newly required information. The
manufacturers already have procedures and methods for developing and
producing the user's manuals, and the additional information required
by the proposed requirements is expected to only add a few printed
pages to these already extensive manuals or documents.
The burden that will occur to manufacturers from the new
requirements for information in the user's manuals will be the effort
required to develop, draft, review, and approve the new information.
The information or data to be contained within the new user
instructions will already be available to the manufacturers from their
design, testing, validation, or other product-development documents.
The burden will consist of gathering the relevant information from
these documents and preparing the additional instructions from this
information.
It is estimated that about 3 weeks of professional staff time (120
hours) would be required to gather the required information for a
single model of an x-ray system. It is estimated that an additional 6
weeks (240 hours) of professional staff time would be required to
draft, edit, design, layout, review, and approve the new portions of
the user's manual or information required by the proposed amendments.
Hence FDA estimates a total of 360 hours to prepare the new user
information that would be required for each model.
For a given manufacturer, FDA anticipates that every distinct model
of fluoroscopic system will not require a separate development of this
additional information. Because it is thought highly likely that
several models of fluoroscopic x-ray systems from a given manufacturer
will share common design aspects, it is anticipated that similar means
for meeting the proposed requirement for display of exposure time, air
kerma rate, and cumulative air kerma and the requirement for the last-
image-hold feature will exist on multiple models of a single
manufacturer's products. Such common design aspects for multiple models
will reduce the burden on manufacturers to develop new user
information. Hence the average time required to prepare new user
information for all of a manufacturer's models will be correspondingly
reduced. It is assumed that the applicability of the new user
information developed to multiple models will reduce the average burden
from the 360 hours to about 180 hours per model under the assumption
that each set of user information for a given equipment feature design
will be a applicable to at least two different models of a
manufacturer's fluoroscopic systems. Under this assumption, the total
estimated time for preparing the new user information that would be
required is 36,000 hours, as shown in table 4 of this document.
In each succeeding year the burden will be less, as the reporting
requirement will apply only to the new models developed and introduced
by the manufacturers in that specific year. FDA assumes that every two
years each manufacturer will replace each of its models with a newer
model requiring new user information. The multiple system applicability
of this information is accounted for by also assuming that each new
model only requires 180 hours of effort to develop the required
information. These assumptions result in an estimated burden of 18,000
hours for each of the years following the initial year of applicability
of the proposed amendments, as shown in table 5 of this document.
In compliance with the PRA (44 U.S.C. 3507(d)), the agency has
submitted the information collection provisions of this proposed rule
to OMB for review. Interested persons are requested to send comments
regarding information collection to the Office of Information and
Regulatory Affairs, OMB (see ADDRESSES).
VI. Analysis of Impacts
A. Introduction
FDA has examined the impacts of this proposed rule under Executive
Order 12866, the Regulatory Flexibility Act (5 U.S.C. 601-612), and the
Unfunded Mandates Reform Act of 1995 (Public Law 104-4) (UMRA).
Executive Order 12866 directs agencies to assess all costs and benefits
of available regulatory alternatives and, when regulation is necessary,
to select regulatory approaches that maximize net benefits (including
potential economic, environmental, public health and safety, and other
advantages; distributive impacts; and equity). The agency believes that
this proposed rule is consistent with the regulatory philosophy and
principles identified in the Executive order. In addition the proposed
rule is economically significant under Executive Order 12866 and is
major under the Congressional Review Act. Therefore the proposal is
subject to review under the Executive order.
The Regulatory Flexibility Act requires agencies to analyze
regulatory options that would minimize any significant impact on small
entities. An analysis of available information suggests that costs to
small entities are likely to be significant, as described in the
following analysis. FDA believes that this proposed regulation will
likely have a significant impact on a substantial number of small
entities, and it conducted an initial regulatory flexibility analysis
(IRFA) to ensure that any such impacts were assessed and to alert any
potentially impacted entities of the opportunity to submit comments.
Section 202(a) of the UMRA requires that agencies prepare a written
statement of anticipated costs and benefits before proposing any rule
that may result in an expenditure by State, local, and tribal
governments, in the aggregate, or by the private sector, of $100
million in any one year (adjusted annually for inflation). The UMRA
does not require FDA to prepare a statement of costs and benefits for
the proposed rule because the proposed rule is not expected to result
in any 1-year expenditure that would exceed $100 million adjusted for
inflation. The current inflation-adjusted statutory threshold is about
$110 million.
The agency has conducted preliminary analyses of the proposed rule,
including a consideration of alternatives, and has determined that the
proposed rule is consistent with the principles set forth in the
Executive order and in these statutes. The costs and benefits of the
proposed rule have been assessed in two separate preliminary analyses
that are described in section VI of this document and that are
available at the Dockets Management Branch (see ADDRESSES) for review.
As reviewed below, these preliminary analyses have an estimated upper
limit to the annual cost of $30.8 million during the first 10 years
after the effective date of the proposed amendments. The analysis of
benefits projects an average annual amortized pecuniary savings in the
first 10 years after the effective date of at least $320 million, with
an estimated 90 percent confidence interval spanning a range between
$88.35 million and $1.160 billion. FDA believes this analysis of
impacts complies with Executive Order 12866, and that the proposed rule
is a significant regulatory action as defined by the Executive order.
Because of the preliminary nature of these cost and benefit analyses
and estimates, FDA requests comments on any aspect of their
methodologies, assumptions, and projections. Comments may be
[[Page 76071]]
submitted to the Dockets Management Branch (see ADDRESSES).
B. Objective of the Proposed Rule
The primary objective of the proposed rule is to improve the public
health by reducing exposure to and detriment associated with
unnecessary ionizing radiation from diagnostic x-ray systems, while
maintaining the diagnostic quality of the images. The proposed rule
would meet this objective by requiring features on newly manufactured
x-ray systems that physicians may use to minimize unnecessary or
unnecessarily large doses of radiation that could result in adverse
health effects to patients and health care personnel. Such adverse
effects from x-ray exposure can include acute skin injury and an
increased potential for cancer or genetic damage. The secondary
objectives of this proposed rule are to bring the performance standard
up to date with recent and emerging technological advances in the
design of fluoroscopic x-ray systems and to assure appropriate
radiation safety for these designs. The proposed amendments would also
align the performance standard with performance requirements in current
international standards that were developed since the original
publication of the performance standard in 1972. In several instances,
the international standards contain more stringent requirements on
aspects of system performance than the current U.S. performance
standard. The proposed changes would ensure that the different safety
standards are harmonized to the extent that systems meeting one
standard will not be in conflict with the other. Such harmonization of
standards lessens the regulatory burdens on manufacturers desiring to
market systems in the global market.
The proposed amendments would require particular x-ray equipment
features reducing unnecessary radiation exposure and thereby yielding
net benefits. The amendments are necessary because the market will not
ensure that these equipment features will be adopted without a
government mandate for such features. Purchasers in health care
organizations have no incentive to demand the more expensive x-ray
equipment that would be required by these new amendments because they
perceive no institutional economic advantage in doing so as benefits
accrue mainly to patients. Furthermore, purchasers are more responsive
to physician attention to an immediate need for diagnostic and
interventional efficacy from the equipment than to a prospective
capability to reduce radiation-associated risk to patients many years
in the future. Patients, also focused on their immediate medical needs,
will not demand this equipment because they lack information and
knowledge about long-term radiation risk and about the highly technical
nature of x-ray equipment. Hence these proposed amendments are
necessary to realize the net benefits described in the following
analysis.
C. Risk Assessment
The risks to health that will be addressed by these amendments are
the adverse effects of exposure to ionizing radiation that can result
from procedures utilizing diagnostic x-ray equipment. These adverse
effects are well known and have been extensively studied and
documented. They are generally categorized into two types--
``deterministic'' and ``stochastic.'' Deterministic effects are those
that occur with certainty in days or weeks or months following
irradiation whose cumulative dose exceeds a threshold characteristic of
the effect. Above the threshold, the severity of the resulting injury
increases as the radiation dose increases. Examples of such effects are
the development of cataracts in the lens of the eye and skin ``burns.''
Skin is the tissue that often receives the highest dose from external
radiation sources such as diagnostic or therapeutic x-ray exposure.
Depending on the magnitude of the dose, skin injuries from radiation
can range in severity from reddening of the skin and hair loss to more
serious burn-like effects including localized tissue death that may
require skin grafts for treatment or may result in permanent
impairment. Stochastic effects are those that do not occur with
certainty, but if they appear, they generally appear as leukemia or
cancer one or several decades after the radiation exposure. The
probability of the effect occurring is proportional to the magnitude of
the radiation dose in the tissue.
The primary risk associated with radiation is the possibility of
patients developing cancer years after exposure, and the magnitude of
this cancer risk is generally regarded to increase with increasing
radiation dose. Consistent with the conservative approach to risk
assessment described by the National Council on Radiation Protection
and Measurements (Ref. 32), we assume a linear relationship between
cancer risk and dose. The slope of this relationship depends on age at
exposure and on gender. Our benefits analysis presented in section VI.H
is based on linear interpolations of cancer-mortality risk per dose
derived from BEIR V table 4-3 (Ref. 22) values reduced by a dose-rate
effectiveness factor of 2 for solid cancers (Ref. 30). The values used
in our analysis are represented in the following graph in figure 1 of
the excess lifetime-probability for death per dose associated with
radiation exposure.
BILLING CODE 4160-01-S
[[Page 76072]]
[GRAPHIC] [TIFF OMITTED] TP10DE02.058
BILLING CODE 4160-01-C
[[Page 76073]]
FDA underscores the overarching uncertainty in these projections
with the following statement adopted from CIRRPC Science Panel Report
No. 9 (Ref. 30):
The estimations of radiation-associated cancer deaths were
derived from linear extrapolation of nominal risk estimates for
lifetime total cancer mortality from doses of 0.1 Sv. Other methods
of extrapolation to the low-dose region could yield higher or lower
numerical estimates of cancer deaths. At this time studies of human
populations exposed at low doses are inadequate to demonstrate the
actual level of risk. There is scientific uncertainty about cancer
risk in the low-dose region below the range of epidemiologic
observation, and the possibility of no risk cannot be excluded.
We project that the equipment features that would be required by
three of the proposed amendments will promote the bulk of radiation
dose reduction and hence cancer risk reduction: (1) Displays of
radiation time, rate, and dose values; (2) more filtration of lower-
energy x rays; and (3) improved geometrical efficiency of the x-ray
field achieved through tighter collimation. We assume that the display
amendment would reduce dose on the order of 16 percent. This assumed
value is one-half of a 32 percent dose reduction observed for several
x-ray modalities in the United Kingdom (UK) between 1985 and 1995. We
assume that one-half of the UK dose reduction was due to technology
improvements alone, whereas the other half stemmed from the quality
assurance use of reference dose levels and patient dose evaluation. The
16 percent dose reduction that we project for the display amendment
thus presumes facility implementation of a quality assurance program
making use of the displayed values. This analysis and other
assumptions--6 percent dose reduction for the filtration amendment, 1
to 3 percent dose reduction for the collimation amendment--are detailed
in Ref. 29. We invite comment on these assumptions.
Until recently, the principle radiation detriment for patients
undergoing x-ray procedures was the risk of inducing cancer and, to a
lesser extent, heritable genetic malformations. Since 1992, however,
approximately 80 reports of serious radiation-induced skin injury
associated with fluoroscopically-guided interventional therapeutic
procedures have been published in the medical literature or reported to
FDA. Many of these injuries involved significant morbidity for the
affected patients. FDA's experience with reports of such adverse events
leads the agency to believe that the number of these injuries is very
likely underreported, given the total number of interventional
procedures currently performed. Additionally, there is the lack of any
clearly understood requirement or incentive for health care facilities
to report such injuries. With the advance of fluoroscopic technology
and the proliferating use of interventional procedures by practitioners
not traditionally specializing in the field, and therefore not
completely familiar with dose-sparing techniques, FDA expects an
increasing risk of radiation burns that warrants the changes to the x-
ray equipment performance standard through the proposed amendments.
D. Constraints on the Impact Analysis
It is FDA's opinion that the proposed amendments would offer public
health benefits that warrant their costs. However, the agency has had
difficulty thus far accessing pertinent information from stakeholders
to help quantify the impact of the proposal and alternatives. In view
of the limited information available with which to develop estimates of
the costs and benefits, FDA solicits comments, data, and opinions as to
whether the potential health benefits of the proposed amendments would
justify their costs. FDA will use all information and comments received
to revise the impact assessment in reaching a final determination as to
the appropriateness of the proposed amendments.
The principal costs associated with the proposed amendments would
be the increased costs to manufacturers to produce equipment that will
have the features required by the amendments. FDA has made an estimate
of potential cost. The cost estimate is based on a number of
assumptions designed to assure that the potential cost is not
underestimated. FDA anticipates that the actual costs of these
amendments to be significantly less than the upper-limit estimate
developed. Manufacturers of diagnostic x-ray systems are urged to
provide detailed comments on the anticipated costs of these amendments
that will enable refinement of these cost estimates.
The benefits that are expected to result from these amendments are
reductions in acute skin injuries and radiation-induced cancers. The
proposed amendments would have two types of impact that reduce patient
dose and associated radiation detriment without compromising image
quality.
The first type of change involves several newly required equipment
features that would directly affect the intensity or size of the x-ray
field. These are the requirements addressing x-ray beam quality, x-ray
field limitation, limits on maximum radiation exposure rate, and MSSD
for mini C-arm fluoroscopic systems. Almost all of the changes that
directly affect x-ray field size or intensity would bring the
performance standard requirements into agreement with existing
international voluntary standards. To the extent that these
requirements are included in voluntary standards that have a growing
influence in the international marketplace, the radiological community
has already recognized their benefit and appropriateness. Moreover,
harmonization within a single international framework would obviate the
expense for manufacturers to produce more than one line of products for
a single global marketplace.
The second type of change that would be required by these
amendments involves the information to be provided by the manufacturer
or directly by the system itself that may be utilized by the operator
to more efficiently use the x-ray system and thereby reduce patient
dose. There is wide support for and anticipation of these new features
by many knowledgeable users of fluoroscopic systems. Similar
requirements were recently included in a new international voluntary
standard.
E. Baseline Conditions
The cost of the proposed amendments to the x-ray equipment
performance standard would be borne primarily by manufacturers of
fluoroscopic systems. The cost for one of the nine proposed amendments
would also affect manufacturers of radiographic equipment and is
discussed in detail in Ref. 28. Therefore, this discussion will focus
primarily on fluoroscopy (i.e., the process of obtaining dynamic, real-
time images of patient anatomy).
X-ray imaging is used in medicine to obtain diagnostic information
on patient anatomy and disease processes or to visualize the delivery
of therapeutic interventions. X-ray imaging almost always involves a
tradeoff between the quality of the images needed to do the imaging
task and the magnitude of the radiation exposure required to produce
the image. Difficult imaging tasks may require increased radiation
exposure to produce the images unless some significant technological
change provides the needed image quality. Therefore, it is important
that users of x-ray systems have information regarding the radiation
exposures required for the images that are being produced in order to
make the appropriate risk-benefit decisions.
Equipment meeting the new standards in the proposed amendments
would provide image quality and diagnostic information identical to
equipment
[[Page 76074]]
meeting current standards. Therefore, the clinical usefulness of the
images provided would not change. The amendments would not affect the
delivery of x-ray imaging services because the reasons for performing
procedures, the number of patients having procedures, and the manner in
which procedures are scheduled and conducted would not be changed as a
result of the amendments. In addition, nothing in these amendments
would adversely affect the clinical information or results obtained
from these procedures. These amendments would result in x-ray systems
having features that automatically provide for more efficient use of
radiation or features that provide the physicians using the equipment
with immediate information related to patient dose, thus enabling more
informed and efficient use of radiation. These amendments would provide
physicians using fluoroscopic equipment with the means to actively
monitor patient radiation doses and minimize unnecessary exposure or
avoid doses that could result in radiation injury.
Estimates of the annual numbers of certain fluoroscopic procedures
performed in the United States during the years 1996 or 1997 were
developed, as described in Ref. 29, using data from several sources.
These estimates of the annual numbers of specific procedures were used
in the estimates of benefit from the proposed amendments. No attempt
was made to account for changes in the annual numbers of procedures in
future years, due to the large uncertainties in making such
projections. FDA also estimates that over 3 million fluoroscopically
guided interventional procedures are performed each year in the United
States. These procedures are described as ``interventional procedures''
because they accomplish some form of therapy for patients, often as an
alternative to more invasive and risky surgical procedures.
Interventional procedures may result in patient radiation doses in some
patients that approach or exceed the threshold doses known to cause
adverse health effects. The high doses occur because physicians utilize
the fluoroscopic images throughout the entire procedure, and such
procedures often require exposure times significantly longer than
conventional diagnostic procedures to guide the therapy.
FDA records indicate that about 12,000 medical diagnostic x-ray
systems are installed in the United States each year. Of these, 4,200
are fluoroscopic system installations. The proposed amendments would
apply only to those new systems manufactured after the effective date,
therefore affecting the 4,200 new fluoroscopic systems installed
annually and a small fraction of radiographic systems that do not
currently meet the proposed standard for x-ray beam quality.
In modeling the x-ray equipment market in the United States for the
purpose of developing estimates of the cost of these amendments, FDA
estimates that there are approximately a total of 40 manufacturers