12 Gy gamma knife radiosurgical volume is a predictor for radiation necrosis in non-AVM intracranial tumors.

PURPOSE: To determine whether the 12-Gy radiosurgical volume (12-GyV) correlates with the development of postradiosurgical imaging changes suggestive of radiation necrosis in patients treated for non-arteriovenous malformation (non-AVM) intracranial tumors with gamma knife stereotactic radiosurgery (GKSRS).

METHODS AND MATERIALS: A retrospective single-institution review of 129 patients with 198 separate non-AVM tumors was performed. Patients were followed with magnetic resonance imaging (MRI) and physical examinations at 3- to 6-month intervals. Patients who developed postradiosurgical MRI changes suggestive of radiation necrosis were labeled as having either symptomatic radiation necrosis (S-NEC) if they experienced any decline in neurologic examination associated with the imaging changes, or asymptomatic radiation necrosis (A-NEC) if they had a stable or improving neurologic examination.

RESULTS: 12-GyV correlated with risk of S-NEC, which was 23% (for 12-GyV of 0-5 cc), 20% (5-10 cc), 54% (10-15 cc), and 57% (>15 cc). The risk of A-NEC did not significantly change with 12-GyV. Logistic regression analyses showed that the following factors were associated with the development of S-NEC: 12-GyV (p<0.01), occipital and temporal lesions (p<0.01), previous whole-brain radiotherapy (p=0.03), and male sex (p=0.03). Radiosurgical plan conformality did not correlate with the development of S-NEC.

CONCLUSION: The risk of S-NEC, but not A-NEC after GKSRS for non-AVM tumors correlates with 12-GyV, and increases significantly for 12-GyV>0 cc.