1133 Biologically Effective Dose and Prediction of Obliteration of Arteriovenous Malformations in Pediatric Patients Treated by Gamma Knife Radiosurgery

INTRODUCTION: Stereotactic radiosurgery (SRS) represents an effective treatment for pediatric arteriovenous malformations (AVMs). Biologic effective dose (BED) is recognized as a predictive variable for outcomes in the adult population, but its role has never been studied in pediatric outcomes. METHODS: Retrospective data for = 18 years old patients treated with single-session SRS for AVM was collected from 1989 – 2019. BED calculations were performed using an a/b ratio of 2.47. Kaplan-Meier analysis was used to evaluate obliteration, new hemorrhage, and radiation-induced changes (RIC). Cox-regression analysis was used for obliteration prediction using two models (margin dose versus BED). RESULTS: One-hundred-ninety-seven patients [median age = 13.1 years, Interquartile range (IQR) = 5.2] were included; 72.6% presented initially with spontaneous hemorrhage. A median margin dose of 22 Gy (IQ = 4.0) with a median BED of 183.2Gy (IQR = 70.54) was used to treat AVMs with a median volume of 2.8 cm3 (IQR = 2.9). Following SRS, obliteration was confirmed in 115 patients (58.4%) using MRI and angiography at a median follow-up of 2.85 years (IQR = 2.26). The cumulative obliteration probability was 43.6% (95% CI = 36.1-50.3), 60.5% (95% CI+=2.2-67.4), 66.0% (95% CI= 56.0-73.7) at 3, 5 and 10 years respectively. In multivariate analysis, a BED >180 Gy [HR = 2.11, 95% CI=1.30-3.40, p = 0.002] in model 1, and a margin dose >20 Gy [HR = 1.90, 95% CI = 1.15-3.13, p = 0.019] in model 2, were associated with obliteration. An AVM nidus volume >4 cm 3 was associated with lower obliteration rates in both models. The probability of symptomatic RIC at 10 years was 8.6% (95% CI = 3.5-13.4). Neither BED nor margin dose were associated with RIC occurrence, with the only predictive factor being deep AVM location [HR = 3, 95% CI = 1-9.1, p = 0.048]. CONCLUSIONS: This study confirms BED as a predictor for pediatric AVM obliteration. Optimization of BED in pediatric AVM SRS planning may improve cumulative obliteration rates.