Study of dose-response relationships for late somatic effects of low neutron doses

Complete observation of survival and late pathology was conducted on over 2000 female mice irradiated with single doses of 1.5 MeV neutrons (5, 10, 20, 40, 80, 160 mGy) and X rays (40, 80, 160, 320, 640, 1280, 2560 mGy). The results showed a statistically life shortening for neutron doses not lower than 80 mGy. Assuming linear non-threshold dose-effect relationships for both radiation qualities, a neutron RBE of 12.3 was obtained. Solid tumour induction was also significant from a neutron dose of 80 mGy and for X-ray doses larger than 1 Gy. No sublinear dependence of the carcinogenic effect on low neutron doses was seen. Separate examination of ovarian tumour induction indicated that a threshold dose is likely to exist, especially for X rays. A trend analysis of the neoplasm incidence confirmed the above findings. Death rate analysis by the Weibull model showed agreement between the shift to earlier times and tumour induction. (author)