Radiobiological effectiveness of high LET radiation

The effect of cyclotron-produced neutrons (30 MeV d → Be) on an animal tumors was studied. The experimental tumors were 5th generation isotransplants of spontaneous mouse squamous cell carcinoma. C3Hf/He mouse were used throughout. Cell survival was examined by the TD50 method after neutron or x-ray irradiation. Tumor regrowth was also analysed by measuring tumor size daily. Results indicated that RBE was higher at low dose level, tumor cells surviving a neutron dose were not capable of repairing potentially lethal damage, and the OER was less after neutrons than after x-rays. Implications of these results in radiation oncology and therapy were discussed. (auth.)