Effects of single dose supervoltage whole brain radiation in Macaca mulatta.

Three groups of four Macaca mulatta were exposed respectively to a single dose of 1000, 1500, and 2000 rads of 20 MeV whole brain radiation with one animal from each group and a control scheduled for sacrifice at 6, 12, 18, and 24 months. With 1000 rads there were no abnormalities. The characteristic lesions in the animals exposed to 1500 and 2000 rads were small foci of delayed radiation necrosis that in the acute phase were relatively large due to marked local accumulation of edema fluid and at later stages were decreased in volume and showed early mineralization. Correspondingly the monkeys frequently showed papilledema, evidently from brain swelling, as the initial clinical finding, and upon histological examination at later stages, brain atrophy and ventricular dilatation. After exposure to 1500 rads the necrotic process was primarily in the white matter of the cerebral hemisphere and progressed from a small number of lesions in this location at 6 months to confluent necrosis at 12 months. At 18 and 24 months, although there was no evidence of further necrosis, there was evidence of increasing gliosis and at 24 months the occurrence of three independent glioblastomas. With exposure to 2000 rads there was a profuse wide scatter of focal necrotic lesions with a predilection for the basis pontis and a clinical deficit inconsistent with survival past 6 months. Accumulation of minute mineral deposits and atherosclerotic plaques were also noted in these monkeys and appeared to be related to both dose and survival time.