biological effectiveness of JRR-4 epithermal neutron beam; Experiment under free air beam and in water phantom (Cooperative research)

Yamamoto, Tetsuya*; Yamamoto, Kazuyoshi ; Matsumura, Akira*; Kumada, Hiroaki; Kishi, Toshiaki ; Hori, Naohiko ; Torii, Yoshiya ; Horiguchi, Yoji; Nose, Tadao*

The surviving curve and RBE of dose components generated in boron neutron capture therapy (BNCT) were separately determined in neutron beams at JRR-4. Surviving fraction of V79 cell with or without B was obtained using an epithermal neutron beam (ENB), a mixed thermal-epithermal neutron beam (TNB-1), and a thermal neutron beam(TNB-2), which were used or planned to use for clinical trial. The cell killing effect of these beams depended highly on the neutron beam used, according to the epithermal and fast neutron content in the beam. RBE of the boron capture were 3.990.24, 3.040.19 and 1.430.08, RBE of the high-LET dose components based were 2.500.32, 2.340.30 and 2.170.28 for ENB, TNB-1 and TNB-2, respectively. The experimental determination of biological effectiveness factor outlined in this paper is applicable to the dose calculation for each dose component of the neutron beams and contribute to an accurate RBE as comparison with a neutron beam at a different facility employed in ongoing and planned BNCT clinical trials.