Frameless Angiography–Based Gamma Knife Stereotactic Radiosurgery for Cerebral Arteriovenous Malformations: A Proof-of-Concept Study

Background: Traditional Gamma Knife radiosurgery (GKRS) of brain arteriovenous malformations (AVMs) using digital subtraction angiography (DSA) requires head immobilization using a stereotactic frame. Objective: We describe our protocol of frameless GKRS using DSA while maintaining high spatial resolution for precision. Methods: This study is a retrospective review of patients with unruptured AVMs who underwent frameless GKRS. Magnetic resonance imaging and 3-dimensional DSA were obtained without a stereotactic frame for all patients. The imaging studies were merged for contouring of the AVM nidus. During GKRS treatment, patients were immobilized using an individually molded thermoplastic mask. Results: Thirty-one patients were included in the analysis. The median age is 45.0 years (interquartile range [IQR]: 28.0–55.0). The median nidus size is 3.0 cm (IQR: 2.0–3.4). One patient had a Spetzler-Martin grade I, 11 had a grade II, 11 had a grade III, 6 had a grade IV, and 2 had a grade V AVM. Eleven patients underwent preradiosurgical embolization, 3 patients had previous microsurgical resection and/or embolization, and 1 patient had prior radiosurgery. The median administered dose was 20 Gy (IQR: 18.0–21.0). All patients completed their treatment with the planned radiation dose without complications. Conclusion: This is the first study that integrates DSA in the treatment planning of brain AVMs using GKRS without utilizing a stereotactic head frame. Frameless GKRS provides numerous advantages over frame-based techniques including improved patient experience and the capability of fractionation and thus expanding the eligibility of more AVMs for radiosurgery, while maintaining high spatial resolution of the AVM using angiography data.