Gamma knife radiosurgery for large volume brain tumors: an analysis of acute and chronic toxicity.

Gamma Knife radiosurgery is often used to treat intracranial tumors <4 cm (approximately 13.5 cm3) in mean diameter. Larger lesions are rarely treated because of the expectation that increasing target volume will increase toxicity. We retrospectively analyzed 35 patients with primary or metastatic brain tumors of more than 13.5 cm3 treated with the Gamma Knife. Only 3 (8.5%) patients developed acute clinical toxicity. Nine (25%) patients developed post-Gamma Knife radionecrosis based on imaging studies, with only 3 of these patients (9% of the study population) having clinical progression of symptoms. Necrosis was not found to be related to prescribed dose, treatment volume or number of treated isocenters. We found no undue toxicity from the treatment of large brain tumors with the Gamma Knife.