Lethal Effects on Rats of Single and Multiple Exposures of 400-Kv and 22-Mv X-Radiation

Abstract

Irradiation of rats with single doses of 400-kvp and 22-Mv X-irradiation showed that the latter is only about 75% as effective when based on the LD50(30). When rats were irradiated with fractionated exposures of 51 r/day, the lethal effectiveness of 22-Mv X-rays (based on accumulated exposure at the time 50% of the animals had died) was only 55 to 60% of that of the 400-kv radiation. This may be due to the lower effectiveness of the daily exposure (51 r) of 22-Mv X-rays, which permitted greater recovery. Calculation showed that the integral dose delivered by 22-Mv X-rays is about 106% of the 400-kvp dose. Thus the greater effectiveness of the 400-kv radiation cannot be explained on the basis of dose distribution in the animals. Gross pathological examinations did not reveal differences in response to the 2 types of radiation. Pulmonary hemorrhages and pneumonia were predominant as the cause of death in both groups. The effectiveness of the 22-Mv X-rays as determined in the present investigation agrees, at least roughly, with that found by Quastler for rats and by Haas et al for rabbits in single exposures, and for tumor therapy over a 5-week period.