Influence of age on life shortening and tumor induction after X-ray and neutron irradiation.

The main object of this study is to investigate the role of age on the susceptibility to radiation carcinogenesis and life shortening for different qualities of radiation. Over the last few years, a line of research at the Laboratory of Pathology, C.R.E. Casaccia, has been set up to study the effects of exposure to neutron irradiation, including observations on late effects (both neoplastic and nonneoplastic) as a function of radiation dose and of age at irradiation. Graded single doses of X rays or attenuated fission neutrons have been given to male BC3F1 mice 3 and 19 months old and to animals in utero at 17 days postcoitum. The analysis of data from over 3000 mice indicates that irradiation at 3 months of age causes life shortening which is associated with the incidence and rate of radiation-induced neoplasms. Prenatal irradiation or irradiation at 19 months of age does not show a clearly measurable life shortening for both X-ray and neutron exposures. However, significantly higher incidence and rate of solid tumors and reticulum cell sarcomas were observed. In general the data confirm the higher biological effectiveness of neutrons compared with X rays. The estimates of neutron relative biological effectiveness for different end points were found to be in the range of 3 to 18 and their variation was closely dose dependent.