Photon and electron specific absorbed fractions to pregnant female organs from maternal and fetal sources.

Radiation dosimetry during pregnancy has traditionally focused on fetal protection, while maternal organ doses from internal radionuclide exposures have received comparatively little attention. Existing Specific Absorbed Fraction (SAF) datasets for pregnant women are limited by simplified phantom geometries, restricted gestational resolution, and inadequate representation of fetal source organs. This study presents a comprehensive set of photon and electron SAFs for maternal target organs, computed using a library of anatomically realistic hybrid pregnant female and fetal phantoms representing eight gestational stages (8, 10, 15, 20, 25, 30, 35, and 38 weeks). Using MCNP6.2 Monte Carlo radiation transport simulations, SAFs were calculated for 55 maternal target regions across 82 source regions-comprising 70 maternal and 12 fetal sources-over 27 energy bins spanning 1 keV to 10 MeV for both photons and electrons, resulting in 35,424 total simulations. Photon SAFs exhibited pronounced gestational dependence for select maternal organs; for example, the photon SAFs to the maternal ovaries from the maternal thyroid source at 100 keV increased approximately sixfold from 8 to 38 weeks. Fetal soft tissue sources produced even greater gestational variability across multiple maternal targets. Electron SAFs demonstrated parallel gestational trends, with uterine self-irradiation SAFs decreasing by roughly a factor of five across pregnancy. S values for 131I were also derived to illustrate practical dosimetric applications, revealing substantial gestational variation for radiosensitive maternal organs. Comparisons with stylized phantoms and the ICRP adult female reference phantom revealed meaningful differences, underscoring the importance of pregnancy-specific, anatomically realistic models. This dataset provides an essential resource for accurate maternal internal dosimetry in medical, occupational, and environmental radiation exposure scenarios.