Survival responses and potentially lethal damage repair of normal 10T1/2 and its transformed TCL 15 cells after irradiation with 43 MeV proton produced neutrons.

Normal 10T1/2 fibroblasts and their transformed counterparts (TCL 15) were used in order to evaluate the RBE, TGF and PLD repair for a therapeutic fast neutron beam (43 MeV proton----Be). For plateau-phase culture, the RBE of 10T1/2 cells were 2.0 and 1.7 at 10 and 1% survival levels respectively and 1.3 from D0. The corresponding RBE values of TCL 15 cells were 2.1, 1.8 and 1.5, and thus the TGF values were 1.05 and 1.1 respectively at 10% and 1% survival levels and 1.8 from D0. For log-phase culture, the survival responses of 10T1/2 and TCL 15 cells to 60Co gamma-rays or neutrons were not significantly different (the RBE at 10% was 2), and thus the TGF value was unity. For neutrons, as a rule no PLD repair has been reported in vitro and in vivo in previous studies. However, in the present study PLD repair occurred in plateau 10T1/2 and TCL 15 cells irradiated with neutrons.