LINAC Based Stereotactic Radiosurgery for Avms: A Single Institutional Experience

Introduction: While Gamma Knife radiosurgery is an established treatment strategy for AVM, the efficacy of LINAC based SRS is less well characterized. Larger AVMs pose unique challenges in radiation strategies often necessitating hypofractionated strategies as they have been shown to be associated with improved obliteration, lower hemorrhage rate and decreased toxicity compared to larger treatment fields in a single fraction. This study analyzes our long-term experience with Linac based SRS in AVM with a special emphasis on hypofractionated patients, examining treatment and outcome metrics.

Methods: We reviewed patients with brain AVM who underwent LINAC based SRS at our institution from March 2008-July 2021. Patients were treated on a LINAC with a micro-multileaf collimator, cone-beam CT imaging and a relocatable facemask. Patients received serial MRI follow-up. Obliteration was determined via MRI or angiography.

Results: 83 patients were included in the study. 59 patients underwent single-fraction SRS and 24 had hypo-fractionated SRS. Of the 24, 12 had two fractions and the remaining 12 had five fractions. For the hypofractionated cohort, the treatment plan was either 24 Gy over 2 fractions (12 Gy x 2) or 30 Gy over 5 fractions (6 Gy x 5). Median follow up was 42 months for a single fraction, 56 months for two fractions, and 28 months for five fractions. Complete obliteration rate at median follow up was noted to be 41% in the single fraction, 50% in two fraction, and 25% in the five fraction.

Conclusion : LINAC-based SRS is an alternative modality to perform radiosurgery for AVMs that carry a higher operative risk. Our results demonstrate the feasibility of LINAC hypofractionated SRS. Further work will be done to expand the cohort and compare outcomes of matched cohorts between the single fractions and hypofractionated groups.