Long-term effects of a single whole-body exposure of mice to ionizing radiations - II. Causes of death

Abstract

The causes of death in mice exposed at the age of 30 days to a single whole-body dose of 15 MeV X-rays have been analyzed from the point of view of both percentage incidence and distribution in time. Ten groups of death causes were used, based on post-mortem findings. In the lower dose groups (50 to 457 r), the percentage incidence was found, in most cases, to vary very little with dose, but some diseases, e.g. leukaemia, did show a definite increase, and others, e.g. pulmonary tumours, a definite decrease with increasing dose. The changes in incidence were linearly related to the dose. The analysis of survival curves for each cause of death separately has revealed that while all causes were advanced by radiation, some were advanced more than others. A definite correlation was found between the acceleration of a given cause of death and the rate of change of the percentage incidence with dose. This suggests that the change of incidence is merely the result of the changed times of onset of disease; an actuarial correction has confirmed this suggestion. It is concluded that the probability of any one disease occurring remains the same in irradiated as in the control animals, the main effect of the radiation being an advancement, at different rates, of all causes of death. The age of the animal at irradiation may be an important factor in determining the relative acceleration of the different diseases. In the high dose groups (549 to 780 r) a definite decrease in incidence of neoplastic diseases has been established. This may be due to a 'radiotherapeutic' effect in cells which later in life might have become manifest as neoplasms.