Development and Implementation of a New Set of Anthropomorphic Phantoms for Dosimetry of the Japanese Atomic Bomb Survivors

Abstract

For many years, the dose estimates calculated at the Radiation Effects Research Foundation (RERF) for the Japanese atomic bomb survivors in Hiroshima and Nagasaki have relied on models of the human body (phantoms) developed in the 1980s. These phantoms are based on primitive geometrical shapes such as rods and cones and offer only three models to represent all age ranges from newborn to adult. These models included male and female sex organs (hermaphroditic in design) with no body differences by sex. Furthermore, no specific model of the female with a fetus was available to use for survivors who were exposed during pregnancy at the time of a bombing. A binational working group has recently developed a modern set of phantoms with more realistic shapes, six age ranges, and phantoms for pregnant women at four gestational ages, denoted the "J45" phantoms to indicate their bodily dimensions being based on the Japanese population of 1945. The new calculations also include partial body shielding by workbenches for an important group of survivors in Nagasaki factories. We discuss here the changes in the phantoms and the corresponding differences in body transmission factors (body TFs) which quantify body self-shielding for gamma rays and neutrons from the bombs for some important example organs. We discuss how these changes may affect implementation, including trends in differences between new and old calculated doses for the survivor population by distance, given survivor distributions by age and sex. We also discuss additional implementation work, including issues related to the dependence of body TFs on survivor orientation (direction facing vis-a-vis the direction to the bomb) and on bodily position (standing, kneeling, lying down) and the related need to calculate averaged body TFs for survivors without those data (i.e., those without shielding histories). We also discuss remaining issues such as the use of the same body size and shape for each combination of sex and age group, although body size varied among survivors and individual body size data are available for a large part of the cohort.