Therapeutic irradiation and brain injury

Abstract

This is a review and reanalysis of the literature on adverse effects of therapeutic irradiation on the brain. Reactions have been grouped and considered according to time of appearance. The emphasis of the analysis is on delayed reactions, especially those that occur from a few months to several years after irradiation. Over 100 such cases are reported in the literature. Eighty cases were identified in which the patient was given a single course of radiation therapy and in which reasonable estimates of the time-dose-fractionation regimen could be made. Eleven of these patients had been irradiated for cancer of the skin, 17 for other extracranial tumors, 20 for either a pituitary tumor or a craniopharyngioma and 32 for primary brain tumors. All dose specifications were converted into equivalent megavoltage rads. The data were analyzed in terms of total dose, overall treatment time and number of treatment fractions. The data were also analyzed in terms of time-dose-fractionation (TDF) and nominal standard dose (NSD). NSD calculations were done according to the usual Ellis formula and also according to a modification in which the N exponent was −0.44 and the T exponent −0.06. When total dose was plotted against number of fractions, a line with slope 0.44 fitted well with the lower dose limits at which brain necrosis has been reported. Also discussed were acute radiation reactions, early delayed radiation reactions, somnolence and leukoencephalopathy post-irradiation/chemotherapy and combined effects of radiation and chemotherapy.