• Hirotaka Hasegawa, Shunya Hanakita, Masahiro Shin, Takehiro Sugiyama, Mariko Kawashima, Wataru Takahashi, Osamu Ishikawa, Hirofumi Nakatomi, and Nobuhito Saito.
• Department of Neurosurgery, The University of Tokyo Hospital, Tokyo, Japan.
• Neurosurgery. 2020 May 1; 86 (5): 685-696.

BackgroundSingle-session stereotactic radiosurgery (SRS) for large arteriovenous malformations (AVMs) ≥10 mL remains controversial, which is considered as the current size limitation.ObjectiveTo reconsider the size limitation of SRS for AVMs by profoundly analyzing dose-volume relationship.MethodsData on 610 consecutive patients with AVM treated with SRS using regular (18-22 Gy) or low (<18 Gy) prescription doses were retrospectively analyzed. AVMs were classified into 4 groups: small (<5 mL), medium (≥5 and <10 mL), medium-large (≥10 and <15 mL), and large (≥15 mL). The maximum volumes were 22.5 mL (regular-dose group) and 23.5 mL (low-dose group).ResultsWhen treated with regular doses, the cumulative 6-yr obliteration rates for each of the 4 AVM groups were 86%, 80%, 87%, and 79%, respectively; the cumulative 10-yr significant neurological event (SNE) rates were 2.6%, 3.9%, 6.8%, and 5.3%, respectively. Regarding large AVMs, regular-dose SRS resulted in marginally better obliteration rate (6-yr cumulative rate, 79% vs 48%, P = .111) and significantly lower SNE (5-yr cumulative rate, 5% vs 31%, P = .038) and post-SRS hemorrhage rate (8-yr cumulative rate, 0% vs 54%, P = .002) compared to low-dose SRS. Multivariate analyses revealed that regular-dose SRS significantly contributed to increase in the obliteration rate and decrease in SNEs and hemorrhage.ConclusionThe outcomes for large AVMs were generally favorable when treated with ablative doses. Single-session SRS could be acceptable for AVMs up to ≈20 mL if treated with ablative doses.Copyright © 2019 by the Congress of Neurological Surgeons.

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