Monkey brain damage from radiation in the therapeutic range

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Abstract
Twelve Macaca mulatta monkeys received 200 rad of supervoltage radiation to the whole brain/day, 5 days a wk. The course in 4 monkeys was 4 wk for a total dose of 4000 rad; in 4 monkeys, 6 wk for 6000 rad; and in 4 monkeys, 8 wk for 8000 rad. Four unirradiated monkeys served as controls. One from each group, sacrificed at 6 and 12 mo. from start of irradiation, are reported. The results from 4000 rad were negligible; those from 8000 rad, profound, with gross brain destruction. The results from 6000 rad, within the therapeutic range, included at 6 mo. punctate necrotic lesions, 1 mm or less, widely scattered but with a predilection for the forebrain white matter. The reaction to these lesions ranged from an early macrophage response to calcification. Some were accompanied by focal edema. There were occasional examples of vascular endothelial proliferation. In addition, there were patches of dilated capillaries or telangiectasia. Twelve months after 6000 rad there were a few mineralized lesions and innumerable minute deposits of Ca and Fe. A more active process was suggested by widely desseminated areas of teleangiectasia, 6-12 mm in extent. The clinical course from this exposure included papilledema from the 3rd-6th mo. and depressed visual evoked response accompanied by delta activity in the EEG from the 6th-12th mo.