September 15, 1995
A September 9, 1994, information paper for physicians and other health care professionals from FDA and a September 30, 1994, Public Health Advisory provided information on "Avoidance of Serious X-Ray-Induced Skin Injuries During Fluoroscopically Guided Procedures." These advisories recommend that information be recorded in the patient's medical record to permit estimating absorbed dose to the patient's skin. The purpose of the recommendation is to encourage identification of those areas of the skin which are irradiated at levels of absorbed dose that approach or exceed a threshold for injury. Such identification would be important for communication and patient care should symptoms of injury develop and should follow-up procedures be planned that would result in additional irradiation of the same skin areas. In addition, the information may assist physicians and facilities in improving procedures, thereby reducing the potential for injury.
The Agency has been requested to clarify this recommendation regarding:
- Which patients should have such information recorded?
- What information should be recorded?
This document presents the Agency's advice on these questions. Medical facilities are encouraged to implement these or similar procedures in order to reduce the likelihood of radiation-related complications.
WHICH PATIENTS SHOULD HAVE SUCH INFORMATION RECORDED?
The potential for a patient to receive a skin dose approaching the threshold for injury is principally determined by the type of fluoroscopically-guided procedure performed. During development of each examination protocol, the facility should assess whether the procedure may result in a cumulative absorbed dose in skin that approaches or exceeds a threshold for radiation injury. This assessment should also include consideration of whether the procedure is likely to be repeated and whether the interval between procedures might affect the potential for radiation injury.
Determination of those procedures likely to approach the threshold for injury is the responsibility of the facility. This determination should be made using information specific to the facility and any guidelines or standards from relevant medical or professional organizations.
WHAT INFORMATION SHOULD BE RECORDED FOR A PATIENT?
A facility should record in the patient's medical record:
an unambiguous identification of those areas of the patient's skin that received an absorbed dose that may approach or exceed the selected threshold.
Such identification may be through a diagram or narrative description.
The facility may also wish to include in the patient record or supplemental file:
an estimate of the cumulative absorbed dose to each irradiated area of the skin noted in the patient record or sufficient data to permit estimating the absorbed dose to those areas of skin.
No consensus currently exists as to the most effective method for estimating skin dose. For example, the sum of all exposures occurring in an entire procedure is likely to be a significant overestimate of the cumulative absorbed dose to a specific area of skin, except in the event that the x-ray beam is stationary during most of the procedure. Therefore, a facility may wish to include in the recor a statement of the uncertainty in the estimate of cumulative absorbed dose recorded in the patient record or derivable from data in the record.
If the threshold for x-ray-induced skin injuries is likely to be approached or exceeded, the protocol for that specific procedure should include a requirement to discuss with the patient the risk for x-ray-induced skin injuries, and what to do if signs or symptoms of injury develop.
ABSORBED DOSE THRESHOLD FOR RADIATION INJURY TO THE SKIN
Radiation injury to the skin (transient erythema) has been observed at absorbed doses in the skin of about 2 Gy (200 rad). More severe effects may occur following larger absorbed doses. Since individual sensitivities may vary, the FDA suggests that the potential for injury be noted in the patient's record for any procedure the facility determines could result in a cumulative absorbed dose in a specific area of skin equal to or greater than 1 Gy (100 rad).
Some reviewers of this document have suggested that a higher threshold may be appropriate because more-serious injuries to the skin, which are likely to require treatment, require absorbed doses greater than 2 Gy (200 rad). Determining the threshold at which to initiate recording is the responsibility of the facility. Facilities may wish to establish an initial threshold and later modify it based on experience.
PROCEDURES FOR WHICH INFORMATION SHOULD BE REPORTED
Information currently available to the FDA indicates that the following procedures should be included in any list for recording developed by a facility because of their potential for long exposure times:
- Radiofrequency Cardiac Catheter Ablation
- Vascular Embolization
- Transjugular Interhepatic Portosystemic Shunt
- Percutaneous Endovascular Reconstruction
A facility should include other fluoroscopically guided procedures that it determines will approach or exceed the selected threshold. FDA encourages professional and medical specialty organizations to provide expert guidance and advice on procedures performed by their members that should be included in such a list.
ESTIMATING ABSORBED DOSE IN THE SKIN AND ASSOCIATED UNCERTAINTIES
Absorbed dose in the skin from fluoroscopy may be estimated through: (a) direct measurements, such as placing radiation dosimeters on the patient during the procedure; or (b) indirect means, such as collection of specific information for a patient on equipment technique factors combined with patient and procedure characteristics (output rates and system geometry), or such as use of supplementary information obtained with measurement and recording devices attached to the x-ray equipment. A number of such devices are currently commercially available. Each approach to dose estimation has advantages and disadvantages, and all of the approaches involve practical complexities.
The accuracy of any estimate of cumulative absorbed dose in the skin will depend on the specifics of the method chosen. Fortunately, clinical decisions and patient management do not require highly accurate estimates of the cumulative absorbed dose. It is more important that the potential for approaching or exceeding the threshold dose be recognized by providers.
The facility should enlist a medical physicist to assist the clinical staff to: evaluate the protocols for specific procedures, optimize these to reduce patient exposure when appropriate and develop methods for estimating cumulative absorbed doses in skin (and associated uncertainties) when such estimates are required for patient management.
FDA also encourages relevant professional organizations to develop practical guides for estimating absorbed dose in the skin from fluoroscopically guided procedures, and the associated uncertainty of such estimates, for use by facilities. FDA, upon invitation, will participate in the review of such guides in order to foster compatibility with FDA recommendations.