Purpose: The Radiation Effects Research Foundation (RERF) has published two core dosimetry systems â€“ Dosimetry System 1986 (DS86) and 2002 (DS02) â€“ as part of their efforts to retrospectively calculate dose to the Japanese atomic bomb survivors. Great care has been taken to record key epidemiological survivor data, such as posture and shielding; due to computational limitations of the time, however, RERF only modeled three stylized phantoms to represent the population: an infant, child, and adult. Our study aimed to investigate the expected dosimetric impact from using an updated and age-expanded phantom series with their cohort.
Methods: Two new high-resolution voxel phantom series based on the Japanese population of 1945 (J45) have been developed, one covering six ages of both genders and another covering four gestational ages of the pregnant female. Organ doses for both series, including fetal and maternal organ doses, were computed using free-in-air photon and neutron fluences tabulated within DS02 for Hiroshima and Nagasaki exposures. These values were compared to doses from the previous three-member phantom series, where certain organ doses were estimated using a surrogate dose (e.g. fetal doses estimated by adult uterine wall dose).
Results: From the photon and neutron portions of the spectra, organ dose differences of up to 25% and 70% are expected between the old and new series, respectively. These differences are dependent on survivor age and orientation to the bomb. Results also indicated that multiple organ-surrogate pairs are inappropriate, such as using the adult uterine wall dose to approximate fetal brain dose.
Conclusion: Our results demonstrate that the new J45 phantom series offer opportunities for significant improvements in dose assessment for pregnant, non-pregnant, and in-utero members of the atomic bomb survivor cohort. Future work to explore the potential for improved dosimetry will consider shielded scenarios for workers and those inside houses.