Analysis of primate head irradiation with 55-MeV protons

The distribution of the dose to the head of a primate phantom due to 55-MeV proton irradiation was calculated using a clinical radiotherapy treatment planning system, with anatomic definition through computerized tomography scans. Dose profiles, isodose distributions, and differential and integral dose-volume histograms are used to describe the probable proton dose to the brain of rhesus monkeys, irradiated over two decades ago, in which brain tumors have now developed. The dose analysis shows that 59% of the brain received a dose in excess of the reference surface dose, and that portions of the brain received doses greater than 300% of the reference surface dose. The regions of high dose are illustrated in isodose distributions. This information may be useful in evaluating potential tumor induction following radiation exposure.