Fetal organ dose calculator for maternal CT

Computed tomography (CT) is sometimes necessary during pregnancy to diagnose and treat urgent conditions, but accurate fetal dose estimation remains challenging. Prior studies often relied on uterus dose or simplified fetal models, limiting organ-specific assessment.

To develop NCICT3.0 by incorporating detailed computational phantoms of pregnant women and fetuses into NCICT2.0, calculate fetal organ dose coefficients for maternal chest and abdomen-pelvis CT, and evaluate phantom-based estimates against patient-specific CT-based Monte Carlo simulations.

Computational phantoms representing fetal ages from 8 to 38 weeks in cephalic presentation were used in Monte Carlo simulations with a validated CT scanner model. Additional breech-presentation models were created for 10, 15, 20, and 25 weeks. Fetal organ dose conversion coefficients (mGy/mGy) were calculated using a general-purpose Monte Carlo code, MCNPX for maternal chest and abdomen-pelvis CT under multiple scan conditions (80, 100, and 120 kVp; head and body filters). Longitudinal tube current modulation (TCM) was modeled using a generic algorithm, and dose changes were assessed relative to size-adjusted fixed-current scans. Phantom-based fetal organ doses were compared with patient-specific CT image-based models simulated using the GPU-based Monte Carlo code MCGPU.

Comprehensive fetal organ dose coefficients were generated and implemented into NCICT3.0, demonstrating strong organ- and presentation-dependent variability. In maternal chest CT, fetal doses were low but increased with gestational age, whereas in abdomen-pelvis CT, doses were higher and decreased with age due to increased attenuation. Maternal uterus dose consistently underestimated fetal organ doses. The generic longitudinal TCM algorithm showed a reduction in fetal doses, particularly at early gestation. Comparisons with patient-specific simulations showed that fetal age, maternal abdominal perimeter, and maternal body habitus should be considered when selecting the most appropriate pregnancy phantoms for fetal dose calculations.

NCICT3.0 provides a comprehensive fetal organ-level dose library for CT, enabling organ-specific dose estimation and supporting research on dose heterogeneity, risk modeling, and optimization of maternal CT imaging.