AbstractID: 6536 Title: Determining the Appropriate Phantom Thickness Range Required for Automatic Exposure
Control Assessment in Mammography: An Approach Based on a Survey of Patient Attenuation Data
In order to assess the performance of a mammography unit’s automatic exposure control (AEC), a range of phantom thicknesses that encompasses the distribution of patient breast attenuation is required. The American College of Radiology recommends that AEC assessment include exposures with BR-12 or acrylic slabs of at least 2-, 4-, 6-, and 8-cm thicknesses and MQSA specifies performance over a range of 2 to 6 cm. A survey of 6,006 women undergoing mammography was conducted to measure the patient attenuation distribution and estimate the mean glandular dose. For each exposure, the equivalent thickness of BR-12 and acrylic matching the attenuation of the patient was calculated. The resulting distribution was used to assess the range of BR-12 or acrylic slab thicknesses needed to evaluate AEC performance over a clinically relevant attenuation range. The range of equivalent thicknesses was found to be 1.3 to 9.2 cm BR-12 (1.3 to 8.4 cm acrylic). The 10th and 90th percentile corresponds to 3.6 and 6.2 cm BR-12 (3.3 and 5.7 cm acrylic). Patients with attenuation equivalent to a phantom thickness of 2 cm were found to be at the extreme end of the distribution (0.2 percentile level for BR-12,
0.3 percentile level for acrylic). Eight centimeters of BR-12 corresponds to the 99.8
th
percentile and 8 cm of acrylic corresponds to more than the 99.9
th
percentile level, indicating that a patient with attenuation greater than an 8-cm phantom would be quite rare.
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