Specific absorbed fractions for detailed foetal organs from maternal electron sources using gestation-specific pregnant phantoms.

Accurate estimation of foetal dose from maternal intake of beta-emitting radionuclides (e.g.131I,177Lu,137Cs) is essential for protecting the developing foetus and assessing its radiological risks. This study developed a comprehensive dataset of electron specific absorbed fractions (SAFs) from maternal source regions to detailed foetal target organs using the series of anatomically realistic hybrid pregnant female phantoms representing eight gestational stages (8-38 weeks). Monte Carlo radiation transport simulations were performed to compute electron SAFs for 70 maternal source regions and 55 foetal target organs across 20 energies (10 keV-10 MeV). The results revealed a strong dependence of foetal SAFs on maternal-foetal geometry, with adjacent maternal organs (e.g. amniotic fluid, urinary bladder wall) producing markedly higher SAFs than distant sources. Organ-specific analyses showed large variability among foetal targets, particularly for electrons, underscoring the need for organ-level rather than total-body dose estimation. Comparisons with previous datasets based on simplified phantoms demonstrated that anatomical realism and gestation-specific modelling substantially influence dose transfer predictions. The electron SAF dataset presented here, developed with high anatomical and energy resolution, provides an essential foundation for improving foetal internal dosimetry and supporting radiological protection decisions in medical, environmental, and emergency exposure scenarios.