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

Abstract

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 RBEs for acute effects in pig skin and rhesus monkey oral mucosa were significantly less than the RBEs for late effects. This observation has also been noticed clinically. The RBEs 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 ∼200 rad 60Co fractions and ∼2.2 to 2.6 relative to ∼400 rad 60Co fractions. The RBE for radiation myelitis was significantly greater (4.2 to 4.6 relative to ∼270 rad 60Co fractions). The tolerance doses for 50 MeV d→Be neutrons in large animals were ∼2200 rad nγ /6 1 2 weeks for skin contraction, ∼2100 rad nγ /6 1 2 weeks for oromucosal necrosis, ∼1300 rad nγ /4 1 2 weeks for radiation myelitis, and ∼960 rad n γ /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 nγ.