Relationship between phantom failure rates and radiation dose in mammography accreditation

The American College of Radiology Mammography Accreditation Program (ACR MA P) reviews both clinical mammograms and a phantom image to assess clinical and technical quality from each mammography unit. The phantom contains deta ils representing fibers (speculations), speck groups (microcalcifications), and masses. The depiction of these structures by the mammographic system i s scored by medical physicists. The phantom image is taken using the facili ty's exposure technique for a 4.2-cm thick breast of average composition. T he mean glandular dose (MGD) is determined from a set of thermoluminescent dosimeters placed on top of the chest wall edge of the phantom. Phantom sco res and MGD data collected from 1993 to 1999 based on 31 535 unit evaluatio ns are presented in this paper. The relationship between the failure rate f or phantom image quality and MGD has been analyzed. While over all doses th e phantom failure rate was 11%, for doses of 0.26 to 0.50 mGy the failure r ate was 43%. The phantom failure rate fell continuously to about 6% for MGD s in the range of 1.51-2.0 mGy. With further increases in dose, failure rat es began to rise. Factors that may account for these results are presented and discussed. (C) 2001 American Association of Physicists in Medicine.