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

Purpose: To compare size‐specific dose estimate (SSDE) in abdominal fat quantitative CT with another dose estimate D size,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 CTDI vol = 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 D size,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 D size,L was 2.99 mGy ± 0.85 (range, 1.48 ‐ 4.88 mGy); and mean D size,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.