Radiobiological foundation of thermal neutron capture treatment

Five radiobiological problems in thermal neutron capture treatment were considered on the basis of experimental data. As a result of an experiment of irradiation using thermal neutron generated by an atomic pile of Kyoto University, RBE of thermal neutron on cultured B-16 melanoma cells was determined to 2.43. Cultured B-16 melanoma cells did not recovered from sublethal damage when fractionated irradiation of thermal neutron was performed. To know additive effects of 10B-compounds, an amount of 10B-boric acid equivalent to 5 μg/ml of 10B was administered to culture medium for melanoma cells before the irradiation. As a result, Do values when 10B-boric acid was administered before irradiation were 3.3 times as much as those when only thermal neutron was irradiated, and RBE of thermal neutron when 10B-boric acid was administered was 3.04 RBE of 10B(n, α)7Li reaction (3.43) was also calculated. It was pointed out that it was difficult to estimate absorbed dose precisely by 10B(n, α)7Li reaction. It was also necessary to know the movement from proliferation to differentiation of cells accurately when neutron capture treatment using differential plasma of cancer cells was performed. (Tsunoda, M.)