Purpose: To examine behavioral dimensions of treatment outcomes for patients receiving cranial irradiation. Radiation encephalopathy is one of these and refers to significant cognitive and emotional dysfunction following radiation therapy to the brain. Issues of definition, estimated incidence, pathophysiologic mechanisms, and recommended research designs are reviewed in relationship to functional neurobehavioral outcomes.

Patients and methods: Twenty-nine studies of adults receiving therapeutic cranial irradiation (TCI) involving 748 patients and 18 studies of prophylactic cranial irradiation (PCI) involving 368 patients are reviewed. Assessment of patient outcomes are summarized for research published since 1980, with specific attention to adverse changes in cognitive and emotional functioning.

Results: Analyses revealed that 213 TCI patients and 100 PCI patients showed encephalopathy attributed to radiation. Manifestations of the late delayed effects of radiotherapy on brain function are related to patient age, total dose of irradiation, fraction sizes, and timing of chemotherapy. Radiation encephalopathy appears to be more common than the pathologic tissue injury of radiation necrosis. Accurate diagnosis of these neurobehavioral sequelae can require follow-up over a period of years with sensitive assessment procedures.

Conclusions: It is likely that the true incidence of treatment-related side effects of cranial irradiation in adults who survive more than 6 months without brain tumor growth or recurrence has been significantly underestimated. Research designs that include formal neuropsychologic assessment in conjunction with other neurodiagnostic tests can provide more comprehensive evaluation of long-term neurobehavioral outcomes.