Effects of Paired Doses of Whole Body Irradiation in the Rhesus Monkey

Abstract

Experiments were designed to study the effect of paired doses separated by seven or 20 days on the LD50 in rhesus monkeys irradiated with X rays. The rate of recovery from an initial dose of 260 r was studied and a time to half recovery of 4·8 days (14·6 per cent per day) was found; this was contrasted with similar studies in other animals. The effects on the symptoms and on the haemopoietic system of paired doses were compared with those of single session radiation, for although the doses compared were biologically equivalent in the three groups as far as survival was concerned, the actual amount of radiation given to the paired groups was greater. A 7-day gap between the doses showed effects on the peripheral blood counts which resembled in their pattern those obtained with a single exposure; a 20-day gap resulted in a greater delay in recovery of the cells and in a loss of those violent fluctuations which characterised the recovery phase of certain of the blood cells after a single or 7-day paired irradiation. The interval of 20 days would seem to be the important modifying factor, not the dose as such. The relative importance of certain of the symptoms as indicators of prognosis is discussed and it is concluded that the behaviour of the reticulocytes is the best indication of the probable fate of the individual.