220 Outcome Evaluation of Repeat Stereotactic Radiosurgery for Cerebral Arteriovenous Malformations

INTRODUCTION: Repeat stereotactic radiosurgery (SRS) for persistent cerebral arteriovenous malformation (AVM) has generally favorable patient outcomes. However, reporting studies are limited by small patient numbers and single-institution biases. METHODS: This multicenter, retrospective cohort study included patients treated with repeat, single-fraction SRS between 1987 and 2022. The primary outcome was a favorable patient outcome, defined as a composite of nidus obliteration in the absence of hemorrhage or radiation-induced neurological deterioration. Secondary outcomes were obliteration, hemorrhage risk, and symptomatic radiation-induced changes. Competing risk analysis was performed to compute yearly rates and identify predictors for each outcome. RESULTS: The cohort comprised 505 patients [254 (50.3%) males; median (IQR) age, 34 (15) years] from 14 centers. The median clinical and MRI follow-up was 52 (61) months and 47 (52) months, respectively. At last follow-up, favorable outcome was achieved by 268 (53.1%) patients (5-year probability = 50%, 95% CI = 45%-55%). Obliteration was achieved by 300 (59.4%) patients (5-year probability = 56%, 95% CI = 51%-61%). Twenty-eight patients (5.6%) experienced post-SRS hemorrhage with an annual incidence rate of 1.38 per 100 patient-years. Symptomatic radiation-induced changes were evident in 28 (5.6%) patients, with most occurring in the first 3 years. Larger nidus volumes (between 2 and 4cm3, subdistribution hazard [SDH] 0.61, 95% CI 0.44-0.86, p = 0.005; >4 cm3, SDH 0.47, 95% CI 0.32-0.7, p < 0.001) and brainstem/basal ganglia involvement (SDH = 0.6, 95% CI = 0.45-0.81, p < 0.001) were associated with reduced probability of favorable outcome. CONCLUSIONS: Repeat stereotactic radiosurgery confers reasonable obliteration rates with a low complication risk. With most complications occurring in the first three years, extending the latency period to 5 years generally increases the rate favorable patient outcomes and reduces the necessity of a third intervention.