RISK ANALYSIS OF LINEAR-ACCELERATOR RADIOSURGERY

Purpose: To evaluate the toxicity of stereotactic single-dose irradiat ion and to compare the own results with already existing risk predicti on models. Methods and Materials: Computed tomography (CT) or magnetic -resonance (MR) images, and clinical data of 133 consecutive patients treated with linear accelerator radiosurgery were analyzed retrospecti vely. Using the Cox proportional hazards model the relevance of treatm ent parameters and dose-volume relationships on the occurrence of radi ation-induced tissue changes (edema, localized blood-brain barrier bre akdown) were assessed. Results: Sixty-two intraparenchymal lesions (ar teriovenous malformation (AVM): 56 patients, meningioma: 6 patients) a nd 73 skull base tumors were selected for analysis. The median follow- up was 28.1 months (range: 9.0-58.9 months). Radiation-induced tissue changes (32 out of 135, 23.7%) were documented on CT or MR images 3.6- 58.7 months after radiosurgery (median time: 17.8 months). The actuari al risk at 2 gears for the development of neuroradiological changes wa s 25.8% for all evaluated patients, 38.4% for intraparenchymal Lesions , and 14.6% for skull base tumors. The coefficient: total volume recie ving a minimum dose of 10 Gy (VTREAT10) reached statistical significan ce in a Cox proportional hazards model calculated for all patients, in traparenchymal lesions, and AVMs. In skull base tumors, the volume of normal brain tissue covered by the 10 Gy isodose line (VBRAIN10) was t he only significant variable. Conclusions: These results demonstrate t he particular vulnerability of normal brain tissue to single dose irra diation. Optimal conformation of the therapeutic isodose line to the 3 D configuration of the target volume may help to reduce side effects. Copyright (C) 1996 Elsevier Science Inc.