Room: Track 3
Purpose: The Radiation Effects Research Foundation (RERF) has published two core dosimetry systems – Dosimetry System 1986 (DS86) and 2002 (DS02) – as part of their efforts to retrospectively calculate dose to the Japanese atomic bomb survivors. Both dosimetry systems base their dose estimates on particle transport simulations coupled with human models (phantoms). Due to computational limitations of the time, however, RERF modeled only three age groups to represent the entire Japanese population: infant, child, and adult. Our groundwork studies have investigated the expected dosimetric impact from using updated phantom technology and computational methodology with the RERF cohorts.
Methods: Two new high-resolution phantom series based on the Japanese population of 1945 have been developed, one covering six ages of both sexes and another covering four gestational ages of the pregnant female. Organ doses for the new phantom series were compared against previous dose estimations by recreating the Hiroshima and Nagasaki exposures within Monte Carlo code using photon and neutron fluences tabulated within DS02. For implementation purposes, response function methodology was established to allow the rapid conversion of angular- and energy-dependent fluences to updated organ doses within the dosimetry system. Additionally, the uncertainty of in-utero organ dosimetry due to unknown fetus orientation within the womb was quantified.
Results: From the photon and neutron portions of the atomic bomb spectra, organ dose differences of up to 25% and 70% are expected between the old and new series, respectively. The development of response functions provided equivalent improvements in dosimetry with extensibility to fluence data for any given survivor. Variations in fetal position within the womb were shown to cause dose uncertainties of up to 20%.
Conclusion: These studies demonstrate that our updated methodology can provide significant improvements in dose assessment for certain pregnant, non-pregnant, and in-utero members of the atomic bomb survivor cohorts.
Funding Support, Disclosures, and Conflict of Interest: The Radiation Effects Research Foundation is a public interest foundation funded by the Japanese Ministry of Health, Labour, and Welfare and the US Department of Energy. This work was supported by RERF Research Protocol 18-59. The views of the authors do not necessarily reflect those of the two governments.