266 Outcome Evaluation of Volume-Staged Stereotactic Radiosurgery for Cerebral Arteriovenous Malformations

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INTRODUCTION: Single-session stereotactic radiosurgery (SRS) has limited role for large arteriovenous malformations (AVM). Volume-staged SRS (VS-SRS) is used to optimize outcomes but studies reporting results are limited. METHODS: This multicenter retrospective cohort of 378 patients from 21 centers reports results of VS-SRS for the entire AVM nidus. We report favorable outcome, obliteration, hemorrhage, and permanent symptomatic adverse radiation effect (ARE) rates. RESULTS: The median age was 31 years (Interquartile [IQR]: 19-44) at the first volume stage, with patients treated in 2–4 stages. The median total nidus volume was 21 cm3 (IQR: 13.9-30.1 cm3) and a median prescription dose of 17 Gy (IQR: 16-18Gy) was used. The median radiographic and clinical follow-up were 48 and 55 months, respectively. Seventy-seven (20.4%) patients had a favorable outcome, with the 3- and 5-year rates being 3.9% and 18%. 127 (33.6%) patients achieved obliteration, with the 3- and 5-year rates being 6.8% and 26%. Obliteration rates of AVMs <15 cm3 were 81% and 31%, respectively. The latency period hemorrhage incidence rate was 3.02 cases per 100 patient-years; 52 patients (13.8%) had a bleed. Seventy-two patients (19%) had symptomatic ARE; in 38 (10.1%) these were permanent. Total nidus volume, prescription dose at first stage, diffuse nidus, and prior hemorrhage were all independent affecting outcome rates. CONCLUSIONS: VS-SRS can be used to treat large AVMs as a standalone treatment. Obliteration rates and favorable outcomes are lower than with smaller AVMs, and repeat treatment is often required. Optimizing treatment plans, by increasing prescription doses, reducing treatment volume at each stage, and increasing the number of stages, may lead to better outcomes.

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