SU‐F‐I‐33: Estimating Radiation Dose in Abdominal Fat Quantitative CT

Abstract

Purpose:To compare size‐specific dose estimate (SSDE) in abdominal fat quantitative CT with another dose estimate Dsize,L that also takes into account scan length.Methods:This study complied with the requirements of the Health Insurance Portability and Accountability Act. At our institution, abdominal fat CT is performed with scan length = 1 cm and CTDIvol = 4.66 mGy (referenced to body CTDI phantom). A previously developed CT simulation program was used to simulate single rotation axial scans of 6–55 cm diameter water cylinders, and dose integral of the longitudinal dose profile over the central 1 cm length was used to predict the dose at the center of one‐cm scan range. SSDE and Dsize,L were assessed for 182 consecutive abdominal fat CT examinations with mean water‐equivalent diameter (WED) of 27.8 cm ± 6.0 (range, 17.9 ‐ 42.2 cm). Patient age ranged from 18 to 75 years, and weight ranged from 39 to 163 kg.Results:Mean SSDE was 6.37 mGy ± 1.33 (range, 3.67–8.95 mGy); mean Dsize,L was 2.99 mGy ± 0.85 (range, 1.48 ‐ 4.88 mGy); and mean Dsize,L/SSDE ratio was 0.46 ± 0.04 (range, 0.40 ‐ 0.55).Conclusion:The conversion factors for size‐specific dose estimate in AAPM Report No. 204 were generated using 15 ‐ 30 cm scan lengths. One needs to be cautious in applying SSDE to small length CT scans. For abdominal fat CT, SSDE was 80–150% higher than the dose of 1 cm scan length.