Attempt to re-estimate organ doses of victims in non-homogeneous exposure accident by means of the state-of-the-art Mesh-type Reference Computational Phantom; A Case study of an IR-192 source accident

Kowatari, Munehiko*; Yoshitomi, Hiroshi   ; Tani, Kotaro*; Tanimura, Yoshihiko   ; Kurihara, Osamu*

This study attempted the reconstruction of organ doses of victims who are highly exposed to gamma rays in non-homogeneous exposure accident by a sealed Ir source in Gilan, Iran. According to the accident report by International Atomic Energy Agency (IAEA), a victim was highly exposed on his right chest and the dose estimation by means of biodosimtry and clinical observation were carried out. However, dose reconstruction by means of physical dosimetry was not completely made. In this study, a series of Monte Carlo (MC) calculations employing the PHITS 3.24 incorporated with the Adult male Mesh-type Reference Computational Phantom was performed to estimate organ doses with reference to an actual radiation accident involved in the Ir sealed source, and to investigate issues on reconstruction of organ doses of victims who are highly exposed to radiation under non-homogeneous exposure accident. Calculated organ doses for the lungs, the red born marrow, and the small intestine by MC calculation were compared with experimental values taken from the literature and were within 23% in terms of mGy h /Ci for the Gilan case. The averaged whole body dose was estimated to be 0.31 Gy, which are less than one-tenth than that estimated by biodosimetry (3.1-4.1 Gy). In the IAEA Gilan report, the average whole body dose was assumed to be 2 Gy for rough estimation of physical dose, having a large discrepancy with those estimated by the MC calculation.