The Effect of High-Energy Proton Irradiation on the Cardiovascular System of the Rhesus Monkey

Abstract

There are no data available about the physiological response of mammals to total-body proton irradiation. Previous studies (1) have dealt with either the effects of focal irradiation or mortality after total-body irradiation. The present study was undertaken to compare the effects of total-body 'y-irradiation and proton irradiation on the cardiovascular system of the rhesus monkey. The effects of proton irradiation on blood pressure, heart rate, electrocardiogram, cardiac output, and the response to norepinephrine were studied at energies of 32, 55, 138, and 400 Mev. A single dose of about 3900 rads to the surface was used, since previous studies with y-rays (2) showed that this dose produced a pronounced fall in blood pressure, without signs of focal neurological damage and in the absence of significant fluid and electrolyte imbalance. Although differences in depth-dose distribution, particularly at low energies, preclude the calculation of a meaningful relative biological effectiveness (RBE) (3, 4), the data from the proton-irradiated animal are compared to data from y-irradiated animals. This comparison shows a similarity between the effect of total-body y-irradiation and proton irradiation at high proton energies and a dependence of the effects on depth-dose distribution at low proton energies.