Biological effects of 15 MeV neutrons

Pathologic effects of fractionated fast neutrons or photons on the pancreas, pylorus and duodenum of dogs

Thirty-nine adult male Beagles received either fast neutron or photon irradiation to the right thorax to determine the relative biological effectiveness (RBE) of fast neutrons on normal pulmonary tissue. The right anterior abdomen was included in the field of radiation. Twenty-four dogs (six/group) received fast neutrons with an average energy of 15 MeV to total doses of 1000, 1500, 2250 or 3375 rad in four fractions per week for six weeks. Fifteen dogs received 3000, 4500 or 6750 rad of photons (five/group) in an identical fractionation pattern. All neutron irradiated dogs receiving 3375 and 2250 rad and one receiving 1500 rad developed clinical signs of pancreatic, hepatic and gastrointestinal disturbances. The liver enzymes of these dogs became elevated and they died or were euthanatized in extremis 47-367 days after irradiation. Only one 6750 rad photon dog developed similar signs and died 708 days post-irradiation. Five neutron and 10 photon exposed dogs died of other causes. Neutron-induced lesions in the stomach and duodenum included hemorrhages, erosions, ulcerations and fibrosis. Ulcers perforated the GI tract of five dogs. Pancreatic lesions included degranulation and necrosis of acinar cells, fibrosis ans atrophy. Islet cells were not obviously damaged. All lesions were associated with degenerative and occlusive vascular changes. The RBE of fast neutrons, assessed by clinical signs, gross and microscopic pathology, is approximately 3-4.5 for pancreas and about 4.5 for pylorus and duodenum.

In vivo radiobiology of heavy ions

The radiobiology of heavy charged particles has been investigated with various animal systems in vivo at the Lawrence Berkeley Laboratory using the helium beam from the 184" synchrocyclotron and the carbon, neon, and argon beams from the BEVALAC. Tumor experiments were carried out using the R1 sarcoma in rats and the EMT6 mouse mammary carcinoma, comparing X rays, carbon ions, neon ions, and argon ions. In vivo normal tissue experiments have been carried out with a wide range of tissues including testis, bone marrow, intestinal crypt cells, lens of the eye, esophagus, lung, and the spinal cord. The induction of dominant lethal mutations after irradiation of the testis was assayed by in vitro embryo culture after in vivo irradiation. Experiments were also done with the Harderian gland tumor induction system.