Some effects of 138-Mev protons on primates.

One hundred two primates (Maeaca mulatta) were irradiated with spaced doses of 138 Mev protons ranging from 105 to 1,220 rads. An LD,,,,^,, of 516 ± 30 rads was estimated from the cumulative mortality data. A comparison of the proton LDr,0/;1(, with the LDS0/S0 from a previous study in which primates were irradiated with 2 Mev x-rays provides an estimate of 1.30 ± .09 (S.E.) for the mortality RBE. Adjusting the 2 Mev x-ray LDR0/8O to correspond to the 138 Mev proton dose rate gives an RBE of 1.04. Changes in total leukocyte count, lymphocyte count, neutrophil count, platelet count, hemoglobin concentration, hematocrits, LDH concentrations, and SCOT concentrations indicate an RBE of 1 for 138 Mev protons as compared to 2 Mev x-rays. The only findings which were significantly different between these qualities of radiation were clinical. Considerably more pronounced signs of gastrointestinal injury and hemorrhage were produced by 138 Mev protons as compared to equivalent doses of 2 Mev x-rays.