The FDA Center for Devices and Radiological Health (CDRH) collaborates with the Conference of Radiation Control Program Directors (CRCPD) in a unique federal-state partnership to characterize the radiation doses patients receive and to document the state of the practice of diagnostic radiology. Each year the Nationwide Evaluation of X-ray Trends (NEXT) survey program selects a particular radiological examination for study and captures radiation exposure data from a nationally representative sample of U.S. clinical facilities. Approximately 45 states provide radiation control personnel to conduct the surveys. CDRH staff compiles, analyzes, and publishes survey results on population exposure, radiographic and fluoroscopic technique factors, diagnostic image quality, and film processing quality.
Surveys are repeated periodically to track trends as technology and clinical practices change. Since 1973, NEXT has been conducting surveys on examinations related to the adult chest, abdomen, lumbosacral (LS) spine, upper gastrointestinal fluoroscopy, mammography, computed tomography of the head, dental radiography, and pediatric chest radiography.
From 1973 to 1983 the NEXT program annually surveyed facilities performing twelve common diagnostic x-ray examinations. Exposure data were collected using manual techniques selected for a standard reference patient. With the implementation of automatic-exposure controlled (AEC) x-ray equipment, it became necessary to develop a method to simulate the radiographic attenuation properties of a real patient. The design and production of the CDRH series of patient equivalent x-ray attenuation phantoms resulted from this effort. The phantoms, models composed of selected materials, are designed to drive the AEC system to produce exposures similar to those received by real patients for a wide range of clinical x-ray conditions, i.e., beam kilo-voltage peak (kVp) and beam quality (HVL). At the same time, these phantoms were designed to be economical, easily transportable, and most importantly to yield consistent and clinically representative results.
The first phantoms to be developed by CDRH were the adult chest and the adult abdomen-lumbosacral (LS) spine phantoms. The NEXT adult chest surveys of 1984 and 1986 provided the testing ground for these new phantoms. There are now seven phantoms within the NEXT family: adult posterior-anterior (PA) chest, adult abdomen-LS spine, adult fluoroscopy, dental, pediatric chest, computed tomography (CT), and mammography. The CT head phantom used for NEXT was constructed to conform to the CT dosimetry phantom parameters specified in CFR 1020.33(b) (6). The phantom used for the NEXT mammography surveys is commercially available, and is approximately equivalent to a 4.2 cm compressed breast. Currently, there are no NEXT surveys of mammography planned because data on the U.S. population dose from this exam are collected from the 10,000 annual MQSA inspections using the same mammography phantom. The NEXT adult chest, fluoroscopy, and dental phantoms are also now commercially available.
The NEXT surveys today capture comprehensive data on radiation exposure and quality assurance associated with the practice of selected radiographic examinations. Among the data obtained are the evaluations of film processing quality, the integrity of the film processing darkroom environment, x-ray film image quality, and information about the facility's general practice.
NEXT continues to be recognized as a national resource. NEXT data were used, for example, in the development of the CRCPD Patient Exposure and Dose Guide - 2003 (CRCPD Publication E-03-2). The CRCPD urges that this publication be applied by all state and local radiation control programs in their efforts to minimize patient exposure. Additionally, at the behest of the American College of Radiology (ACR), the American Association of Physicists in Medicine (AAPM) is relying on NEXT data to develop reference exposure values for common diagnostic exams.
NEXT is finding its ways across the U.S. borders, with a number of international organizations and countries requesting NEXT program information as well as phantoms for use in various projects. Organizations expressing such interest include the International Atomic Energy Agency (IAEA), which is developing recommendations for the determination of patient doses in common x-ray exams, and Health Canada, the Canadian equivalent of the FDA, which is engaging in surveys paralleling the NEXT surveys.
One important upcoming technological development, and challenge, NEXT will address is the introduction of digital x-ray imaging technology, where the established relationship between patient exposure and film image quality no longer holds. The impact on patient exposure may be significant as there is no film to under-expose or over-expose. Consequently, one area NEXT will evaluate regarding digital imaging technology is whether or not facilities using digital x-ray systems have lower or higher patient exposure levels compared to those employing standard film systems.
Lastly, as the clinical benefit from common radiographic examinations has improved, from the standpoint of image quality and patient exposure, new technologies have promoted new and increasingly complex exams using CT and fluoroscopic equipment. Future NEXT surveys plan to focus on these types of exams and document their impact on population dose and on imaging.
Nationwide Evaluation of X-Ray Trends (NEXT)
Tabulation and Graphical Summary of 2000 Survey of Computed Tomography Final results of the 2000-01 NEXT CT survey are available now on the Conference of Radiation Control Program Directors, Inc. (CRCPD) web site.