Multistage stereotactic radiosurgery for large cerebral arteriovenous malformations using the Gamma Knife platform

Purpose Radiosurgery is an established technique to treat Cerebral Arteriovenous Malformations (AVMs). Obliteration of larger AVMs (>10–15 cm3 or diameter > 3 cm) in a single session is challenging with current radiosurgery platforms due to toxicity. We present a novel technique of multi-stage stereotactic radiosurgery (SRS) for large intracranial arteriovenous malformations (AVM) using the Gamma Knife system. Materials/Methods Eighteen patients with large (>10–15 cm3 or diameter ⩾3 cm) AVMs, which were previously treated using a staged SRS technique on the Cyberknife platform, were retrospectively selected for this study. The AVMs were contoured and divided into 3-8 sub-targets to be treated sequentially in a staged approach at half to four week intervals. The prescription dose ranged from 15 Gy to 20 Gy, depending on the sub-target number, volume and location. Gamma Knife plans using multiple collimator settings were generated and optimized. The coordinates of each shot from the initial plan covering the total AVM target were extracted based on their relative positions within the frame system. The shots were re-grouped based on their location with respect to the sub-target contours to generate sub-plans for each stage. The delivery time of each shot for a sub-target was decay corrected with 60Co for staging the treatment course to generate the same dose distribution as that planned for the total AVM target. Conformality indices and dose-volume analysis were performed to evaluate treatment plans Results With the shot re-distribution technique, the composite dose for the multi-staged treatment of multiple sub-targets is equivalent to the initial plan for total AVM target. Gamma Knife plans resulted in an average PTV coverage of 96.3%±0.9 and a PITV of 1.23±0.1. The resulting Conformality indices, V12Gy and R50 dose spillage values were 0.76±0.05, 3.4±1.8 and 3.1±0.5, respectively. Conclusion The Gamma Knife system can deliver a multi-staged conformal dose to treat large AVMs when correcting for translational setup errors of each shot at each staged treatment. This article is protected by copyright. All rights reserved.