DOSE COEFFICIENTS FOR THE ICRP PREGNANT-FEMALE MESH-TYPE REFERENCE COMPUTATIONAL PHANTOMS UNDER IDEALIZED EXTERNAL EXPOSURES TO PHOTONS

The present study aimed to establish a comprehensive set of dose coefficients (DCs) for the pregnant woman and fetus under idealized external photon exposures using the pregnant-female mesh-type reference computational phantoms (MRCPs) of the International Commission on Radiological Protection (ICRP) coupled with Geant4 Monte Carlo radiation transport code. The dataset includes 27 organs and detriment-weighted DCs for the pregnant woman and 30 organs and whole-body DCs for the fetus under six idealized irradiation geometries: antero-posterior (AP), postero-anterior (PA), left-lateral (LLAT), right-lateral (RLAT), rotational (ROT), and isotropic (ISO). The DCs exhibited fetal age dependency, with maximum differences of 1.7-fold for the maternal detriment-weighted DCs (0.015 MeV) and 15.4-fold for the fetal whole-body DCs (0.02 MeV) between the 8- and 38-week pregnant-female MRCPs from AP irradiation. These variations reflect anatomical changes during pregnancy, including increased maternal body size and fetal growth, which enhance internal organ shielding in older fetuses. Furthermore, comparisons were made between the maternal uterine DCs and fetal whole-body DCs for the 8- and 10-week fetuses (first trimester) to investigate the applicability of using maternal uterine dose as surrogate for fetal dose. The results showed differences of up to 1.8-fold and 7.7-fold for the 8- and 10-week phantoms, respectively, indicating that fetal DCs should be preferred over maternal uterine doses, particularly for low-energy photon exposures (<0.05 MeV). The established datasets are expected to be used for assessing radiation risk and developing radiological protection guidelines for pregnant women and fetuses in various occupational and public exposure scenarios.