Studies on relative biological effectiveness and therapeutic gain factor of high energy protons modulated for radiotherapy

Various biological effects of 250 MeV proton beam modulated for therapeutic irradiation at Particle Radiation Medical Science Center (PARMS) were examined and compared with those of 180 kV X-rays and Cobalt-60 gamma-rays. RBE values in relation to X-rays on in vitro cell inactivation using HMV-I, NFSa (fibrosarcoma)-C3H/He mice lung colony assay, C3H/He mice acute skin reaction and tumor growth delay of NFSa transplanted in C3H/He mice were 0.95, 0.94 - 0.95, 0.77 - 0.87 and 0.77 - 0.81, respectively. RBE values on in vitro or lung colony assay was higher than that on either skin reaction or tumor growth delay. Dose dependency of RBE was observed in skin reaction. Therapeutic gain factor (TGF) of PARMS protons obtained from RBE values on skin reaction and tumor growth delay was approximately 1.0. (author)