Abstract
The therapeutic gain factor(TGF)of 10B-neutron capture therapy(NCT)was analyzed using transplanting Greene's melanoma and normal skin of hamster. The Kyoto University Research Reactor, which has a very low contamination of γ rays and fast neutrons, was used as a thermal neutron source. Boron-10-paraboronophenylalanine hydrochloride(10B-BPA), which can highly concentrate 10B into melanoma cells, was administered to the hamsters eight hours before thermal neutron irradiation. Then the tumor or the normal skin was irradiated under a condition of 5 MW for 90 minutes. The absorbed dose from NCT was calculated by method of Fairchild(1966). The tumor RBE of NCT obtained by the tumor growth delay time method was 2.2 at 11.5 Gy of NCT. Early skin reactions were recorded two or three times a week after irradiation, according to an arbitrary scale. The maximum skin reaction score was used in the determination of the skin RBE. The skin RBE was 2.1 at 11.1 Gy of NCT. On the bases of these date, the TGF of NCT was calculated as 1.1 (2.2/2.1). There is a significant difference in absorbed dose distribution between the melanoma and the surrounding normal skin on NCT. In consideration of these condition, a “practical” TGF value for pre-clinical evaluation becomes higher.
