Simulation technique on dose-rate distribution in a Co -ray irradiation field

Kaneko, Hirohisa; Haruyama, Yasuyuki; Seito, Hajime; Yamagata, Ryohei; Hanaya, Hiroaki; Kojima, Takuji

Dose-rate distribution in irradiation area of cobalt-60 rays was calculated using a Monte Carlo photon transport code named as EGS-SPG code. The dose rate values measured by the ionization chamber and the alanine dosimeter were compared with calculated ones for the evaluation of the validity of the calculation. As a result, the difference between measurements and the calculation value was within a few % except for a position very near the source for a wide board radiation source. The dose-rate distribution can be estimated using these numerical results at the beforehand planning of a board radiation source arrangement although dose-rate measurement should be done only for a position very near the radiation source, where calculated value disagreed. The dose rate distribution measurement after the radiation source arrangement enables us to save number of the dosimeter and measurement time.