Mechanisms of radiation-induced brain injury are not yet fully understood. Early failure oc-curs because of the eect of ionizing radiation on dividing endothelial cells and oligodendrocytes. Hypothetically, late radiation-induced brain injury is caused by chronic inammation and oxidative stress. In the case of irradiation of the hippocampus, the failure of neurogenesis and cognitive decline could be consequences of such pathological mechanisms. Due to the lack of diagnostic tools that could more precisely dene the brain injury aer irradiation, any therapy that may prevent such consequences in patients who require radiotherapy is currently not known. This article summarizes research hypotheses regarding processes of the brain damage aer radiation, prospects in the diagnosis and therapeutic approaches.