Predictive Factors of Radiation Necrosis after Radiosurgery for Cerebral Metastases

The aim of this study was to determine if the risk of radiation necrosis after radiosurgery is related to the presence of normal tissue included in the prescription volume. Between 1994 and 2001, 377 patients representing 760 lesions were treated by radiosurgery in our center with a 10-MV LINAC. The median age of the patients was 57 years (range 30–86 years), median tumor volume was 4.9 cm 3 , median peripheral dose (70%) was 15.6 Gy and median dose at the isocenter was 21.6 Gy. Karnofsky index, disease control and number of lesions were the only parameters significantly influencing survival (median 8.6 months), while disease-free survival was correlated with the number of isocenters. Seven percent of the patients presented severe complications, including nine episodes of radiation necrosis. The only parameter influencing the risk of radiation necrosis was the conformity index (p = 0.001). These findings emphasize the importance of reducing falsely irradiated normal tissue during radiosurgery to prevent radiation necrosis.