Acute Radiation-induced GI-ARS and H-ARS in a Canine Model of Mixed Neutron/Gamma Relative to Reference Co-60 Gamma Radiation: A Retrospective Study.

Studies performed decades ago in the canine and nonhuman primate established the dose response relationships for the hematopoietic acute radiation syndrome in response to mixed neutron/gamma, x-radiation, and Co gamma radiation. There were no published studies that determined the dose response relationships for the gastrointestinal acute radiation syndrome in response to either noted radiation quality. This analysis of a retrospective, unpublished study provided the dose response relationships in a canine model for the acute gastrointestinal syndrome relative to the acute hematopoietic syndrome due to mixed neutron/gamma radiation. Canines were exposed to total-body, steady state, bilateral, 0.40 Gy min, mixed neutron/gamma (5.4:1) radiation from a TRIGA reactor. The average neutron/gamma energy (MeV) was 0.85/0.9, and exposure was reported as midline tissue dose. Medical management was not administered. The mixed neutron/gamma exposure resulted in an estimated LD50/6 of 2.83 Gy [2.76, 2.94] and LD50/30 of 2.16 Gy [2.01, 2.24] for the GI- and H-ARS respectively. The mean survival times for decedents after mixed neutron/gamma exposure approximate to the LD50/6 were 8.5 d, 10.5 d, and 4 d for 2.75 Gy, 2.80 Gy, 3.00, and 3.12 Gy exposures, respectively. The mean survival times for decedents for mixed neutron/gamma exposure approximate to the LD50/30 were 21.3 d and 15.6 d for 2.00 Gy and 2.25 Gy, respectively. Furthermore, the dose response relationships for the acute hematopoietic syndrome due to mixed neutron/gamma exposure (0.85/0.9 MeV; 5.4:1) resulted in an estimated relative biological effectiveness of 1.2 as compared with reference Co gamma radiation.