Dose calculation using Japanese voxel phantoms for diverse exposures

Saito, Kimiaki  ; Sato, Kaoru   ; Kinase, Sakae   ; Noguchi, Hiroshi; Funabiki, Jun*; Takagi, Shunji*; Sato, Osamu*; Emoto, Yutaka*; Koga, Sukehiko*

The voxel phantoms for Japanese male and female adults developed from CT data have been utilized for radiation protection purposes. User codes based on the EGS4 Monte Carlo program have been constructed to calculate external and internal exposures for photons and electrons. The calculated doses were compared with those using stylized MIRD type and other phantoms. The difference for external dose is not simply explained by the difference in body size, but the positions of organs were found to be an important factor to determine the doses. In internal exposure, the positional relations among organs drastically affect the specific absorption fractions, if the source and target organs are different. The simple approximation which has been used by ICRP to evaluate the dose at the boundary of two different media was found to give S values being too conservative. These calculated data shows the usefulness of realistic voxel phantoms combined with the Monte Carlo calculations.