Author: Benjamin W. Maloney, Ashley E. Rubinstein, Colin Schaeffer, Justin Yu 👨🔬
Affiliation: Henry Ford Health 🌍
Purpose: Radiography AEC systems ensure correctly exposed images for varied kVp and patient thicknesses. The specific kVp and PMMA thicknesses selected for testing AEC tracking may affect passing rates. This analysis seeks to optimize the selection of kVp/PMMA combinations to ensure AEC systems function correctly on all patients while reducing testing that does not add significant value.
Methods: A retrospective analysis was performed on AEC tracking tests from 72 physics surveys of radiographic systems collected over 4 years. Exposure index (EI) data was collected from each test, which was comprised of exposures taken with all combinations 80/100/120 kVp with 6/8/10/12” of PMMA, except 6” PMMA and 120kVp, for a total of 11 kVp/thickness combinations for each AEC system. This set of kVp/PMMA combinations was defined as the “baseline” set. Passing criteria was defined as <35% coefficient of variability (COV) in overall EI values, and <30% COV within a specific kVp station or PMMA thickness. The overall pass rate for all systems was then recalculated for different kVp/PMMA sets, which were defined by excluding certain kVp/PMMA combinations from the baseline set; a total of 7 unique sets of kVp/PMMA data were analyzed.
Results: The pass rate for the baseline set was 79% and 86% for table and wall AEC systems, respectively. For the modified sets, recalculated pass rates rose to 84-89% for table and 86-96% for wall.
Conclusion: The selection of kVp and PMMA thicknesses during testing of AEC tracking impacts the calculated overall failure rate. Selecting less comprehensive kVp/PMMA combinations increased pass rates compared to the baseline set, suggesting that fewer failures would be detected. QMPs should carefully select the combinations of kVp and PMMA thicknesses to cover the range that are predicted to be utilized in clinical exams.