Oncogenic effects of ionizing radiation

In experimental studies the authors observed that following total-body irradiation (150 to 200 R, four times, at weekly intervals, applied to 6- to 8-week-old mice of the C3H strain) 56 out of 116 mice developed leukemia at 8 1/2 months average age and 2 mice developed multicentric parotid gland carcinomas when 6 to 7 months old. None of the 93 untreated controls developed either leukemia or salivary gland tumors. On the other hand, the authors demonstrated in a more recent study that similar exposure of rats, instead of mice, to total-body γ irradiation increased significantly the incidence of solid tumors, such as mammary or ovarian carcinomas, or subcutaneous sarcomas, but it did not increase, to any significant degree, the incidence of leukemia or lymphomas. In an experiment carried out on Sprague-Dawley rats, the incidence of tumors, mostly of the mammary glands (50% of which were carcinomas), increased, following irradiation, from 22 to 93% in females and from 5 to 59% in males. In a similar experiment carried out on Long-Evans rats, the incidence of tumors increased, following irradiation, from 28 to 63% in females and from 10 to 42% in males