Radiation Brain Injury

Cranial irradiation has an important role in the treatment of brain tumors either with curative intent or for palliation. Cranial irradiation has a unique application in prevention of distant metastasis to brain parenchyma, and prophylactic cranial irradiation may be carried out in selected patients at high risk of neoplastic cranial involvement. Brain is also an organ at risk during radiotherapy of tumors which are located in base of skull and in some head and neck cancers. Cranial irradiation in any condition can cause brain injuries that are classified into three groups based on the timing of their occurrence after radiation exposure: acute (during radiation or up to 6 weeks after radiation), early delayed or subacute (up to 6 months after radiation), and late delayed (6 months or more after the completion of radiation). However in more trials, brain injury simply is defined as acute (within 90 days of the commencement of therapy) and late reactions (after 90 days of the commencement of therapy) [1]. Reports indicate that patients that undergo standard fractionated cranial irradiation and stereotactic radiosurgery may have acute brain reactions in the range of 2–40% [1–12]. However, up to 50% of patients with high doses per fraction (more than 3 Gy) to a large part of the brain may develop acute encephalopathy [3, 13].