The Relative Biological Effectiveness of 138-Mev Protons as Compared to Cobalt-60 Gamma Radiation

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Abstract
Adult female white Swiss Webster mice were irradiated with single spaced doses of either 138-Mev protons or Co60 gamma-radiation delivered at 86, 256, and 550 rads/min; the doses were so spaced as to bracket the LD50(30). Clinically, doses of 865 rads and above of the protons produced relatively more gastrointestinal injury than did doses of the same size of Co60 gamma-radiation. Total mortality through 30 days, however, was the same for both types of radiation. Comparison of the LD50(30)''s at all 3 dose rates provided estimates of the proton to Co60 gamma-ray RBE (Relative Biological Efficiency) of approximately 1. The RBE''s determined by comparison of the LD50(6)''s were 10% to 20% higher than those found at 30 days. No dose-rate dependence was found. The results are compared to published data from similar experiments.