S. Shah, S. S. Shah, S. Rastogi, S. Satti, and S. A. Shah; Christiana Care Health Services, Newark, DE
Purpose/Objective(s): The management of high-risk AVMs (mRBAS>1.5) remains controversial with no accepted modality of treatment. Stereotactic Radiosurgery (SRS) has a reported success rate of less than 50% with unacceptably high rates of radiation necrosis with larger AVM volumes. Neither volume staging nor hypo-fractionated SRS have conclusively been demonstrated to improve results. We hypothesized that the failure of previous hypo-fractionation SRS trials was due to an insufficient biologically effective dose of radiation (BED). We initiated a pilot study of treating high risk patients with a total dose divided into three or five fractions designed to deliver the equivalent BED of 20 Gy in a single fraction (a/ß =3). Materials/
Methods: A retrospective analysis was performed of 26 consecutive high-risk AVM patients, defined as having modified Radiosurgery-based AVM Scale (mRBAS) score greater than 1.5, who had a minimum of two years of follow up or underwent obliteration. Patients were treated with either 30Gy/3 fractions, 33 Gy/3 fractions, or 40 Gy/5 fractions using CyberKnife SRS. The primary endpoint was complete AVM obliteration, determined by MRA imaging on long-term follow-up. Most obliterations were confirmed with diagnostic cerebral angiography. Secondary endpoints were post-radiosurgery hemorrhage and radiation related necrosis. Kaplan-Meier analysis was used to determine obliteration rates. Results: From 2013 to 2021, 26 patients fitting inclusion criteria were identified (62% male, average age at treatment = 50.8 years). Ten (42%) patients had prior treatment (surgery, radiosurgery, embolization) for their AVM, 23 (88%) had AVMs in eloquent locations, 11 (46%) had high-risk features, and 10 (38%) experienced AVM rupture prior to treatment. Average mRBAS score was 2.05 (SD=0.44), and mean AVM volume was 8.83 cm 3 (SD= 6.24). Complete AVM obliteration was achieved in 100% of patients after an average of 22.6 (SD= 11.59) months. Kaplan-Meier analysis showed AVM obliteration rates at 1, 2, and 3 years to be 19.3%, 57.7%, and 88.5%, respectively. One patient (3.8%) experienced AVM hemorrhage post- treatment and 3 (12%) experienced radionecrosis. Conclusion: Dose escalated hypofractionated SRS resulted in an 100% AVM obliteration rate in high-risk lesions at an average of 22.6 months. The rate of radiation necrosis was 12%. The SRS dose used in this study is the highest BED of any AVM hypofractionation trial in the published literature. This study suggests that dose escalated hypofractionated radiosurgery can be a successful strategy for high-risk AVMs with acceptable long-term complication rates. Further investigation of this treatment regimen should be performed to assess its efficacy.
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