TH-EF-BRA-03: Size-Specific, Scanner-Independent Fetal Dose Estimates in Abdominal and Pelvic CT Examinations of Pregnant Patients
Purpose: The purpose of this work is to develop patient size-specific, scanner-independent CTDIvol-to-fetal-dose conversion coefficients for abdominal and pelvic CT examinations of pregnant patients of various gestational ages. Methods: For 18 pregnant patients of gestational age ranging from 12 to 36 weeks who underwent clinically-indicated CT examinations, models of maternal and fetal (or embryo) anatomy were created from the image data, and dose to the fetus was estimated using Monte Carlo simulations of fixed tube current helical scans of the abdomen and pelvis for 64-slice MDCT scanners from four major manufacturers. Fetal doses were normalized by scanner-specific 32 cm CTDIvol values and averaged across all scanners to obtain a scanner-independent CTDIvol-to-fetal-dose conversion coefficient for each patient. Patient size was described using water equivalent diameter (WED) measured at the image containing the three-dimensional geometric centroid of the fetus. The coefficient of variation (CoV) across scanners for the simulated fetal dose was calculated before and after CTDIvol normalization to demonstrate the utility of scanner-independent CTDIvol-to-fetal-dose conversion coefficients for each patient. The relationship between the WED patient size metric and CTDIvol-to-fetal-dose conversion coefficients was also examined to determine if a correlation exists. Results: The CoV across scanners for fetal dose in all patients before and after CTDIvol normalization ranged from 25.10%–30.16% and 5.60%–9.48%, respectively. An exponential relationship between CTDIvol-to-fetal-dose conversion coefficients and patient size was observed with a coefficient of determination of 0.84. Conclusion: Strong correlation exists between CTDIvol normalized fetal dose and WED. These results indicate that fetal dose from abdominal and pelvic CT examinations of pregnant patients of various gestational ages may be accurately estimated with: (a) fetal dose normalized by CTDIvol to account for scanner variation and (b) a WED patient size metric to account for patient size variation. Disclosures — Michael McNitt-Gray: Institutional Research Agreement, Siemens AG; Research Support, Siemens AG; Consultant, Flaherty Sensabaugh Bonasso PLLC; Consultant, Fulbright and Jaworski; Disclosures — Erin Angel: Employee of Toshiba America Medical Systems, Inc.