Inactivation of cultured human tumor cells irradiated by cyclotron neutrons and protons

According to the results on cell survival data, we may conclude the followings when concentrating on the radiation qualities of protons and neutrons. 1) Since the sensitivities of several cells to high LET radiation were revealed to be identical, RBE could increase for X-ray resistant cells. 2) In the multifractional therapy planning of X-ray resistant tumor with neutrons, neutron energy should be selected on the basis of appropriate dose distribution with enough energy but not of high LET with lower energy. 3) RBE value on cell survival for protons with the energy used for cancer therapy is ranging between 1.0 - 1.1 and can not be lower than 1.0. 4) The RBE-LET relation for particle radiations with wide energy distribution is almost the same as that for heavy ions even when plotted against dose-average LET. (author)