[Relationship between irradiation and appearance of brain tumors in rats].

Sprague-Dawley rats were exposed to Co 60 irradiation (3 Gy) at different ages. Rats were distributed among sham-control (618 males and 120 females) and exposed groups: foetus (66 males and 65 females), 3 month-old (304 males), and 9 month-old (120 males and 60 females). The incidence of brain tumours was 5.3% in male control rats and nil in female control rats. Brain tumour incidence decreased in 9 month-old rats (3.3%), and increased from 6.6% in 3 month-old rats to 15.2% in male foetuses and 12.3% in female foetuses. Age at incidence of brain tumours decreased in irradiatiated animals. Astrocytomas were the more susceptible type of brain tumours to radiocarcinogenesis.