50-MeVd→Be neutrons: A comparison of normal tissue tolerance in animals with clinical observations in patients☆

The acute and late effects of 50 MeV neutrons were investigated by irradiating a variety of organ systems in large animals using dosage schedules similar to those that have been employed clinically. The RBE's for acute effects in pig skin and rhesus monkey oral mucosa were significantly less than the RBE's for late effects. This observation has also been noticed clinically. The RBE's for late effects in pig skin, rhesus monkey oral mucosa, and rhesus monkey kidney were consistent with values of 3.1 to 3.4 relative to approx.200 rad /sup 60/Co fractions and approx.2.2 to 2.6 relative to approx.400 rad /sup 60/Co fractions. The RBE for radiation myelitis was significantly greater (4.2 to 4.6 relative to approx.270 rad /sup 60/Co fractions). The tolerance doses for 50 MeV/sub d..-->..Be/ neutrons in large animals were approx.2200 rad/sub n..gamma..//6-1/2 weeks for skin contraction, approx.2100 rad/sub n..gamma..//6-1/2 weeks for oromucosal necrosis, approx.1300 rad/sub n..gamma..//4-1/2 weeks for radiation myelitis, and approx.960 rad/sub n..gamma..//4 weeks for radiation nephritis. These values correlate well with clinical observations at TAMVEC, since the majority of soft tissue complications in patients occurred following tissue doses in excess of 2100 rad/sub n..gamma../.