Introduction: Incompletely obliterated intracranial arteriovenous malformations (AVM) after initial treatment with stereotactic radiosurgery (SRS) can be treated with a repeat session of SRS. However, the relative efficacy of repeat versus initial SRS is not well defined. The goal of this retrospective case-control study is to compare the outcomes of repeat versus initial SRS for the treatment of matched cohorts comprising angioarchitecturally similar AVMs.

Methods: We evaluated a prospective database of AVM patients treated with SRS from 1989-2013. AVM patients who underwent repeat SRS with radiologic follow-up =2 years or nidus obliteration were selected for analysis and matched, in a 1:1 fashion and blinded to outcome, to previously untreated AVMs which underwent initial SRS. Statistical analyses were performed to compare the outcomes after repeat versus initial SRS.

Results: The matching processes yielded 84 patients in each of the repeat and initial SRS cohorts (mean margin doses 20.7 and 20.9 Gy, respectively; P=0.74). In the repeat SRS cohort, obliteration was achieved in 67%; the rates of radiologic, symptomatic, and permanent radiation-induced changes (RIC) were 35%, 10%, and 4%, respectively; and the annual post-SRS hemorrhage rate was 3.1%. Compared to the initial SRS cohort, the repeat SRS cohort had significantly lower obliteration rates (P=0.038) and higher post-SRS hemorrhage rates (P=0.04). The RIC rates of the two cohorts were not significantly different.

Conclusions: Repeat SRS yields considerably poorer outcomes than initial SRS for angioarchitecturally comparable AVMs. Further studies in AVM radiobiology and vascular structure are necessary to elucidate this potentially differential response.

Patient Care: Approximately 30% of AVMs remain patent after initial treatment with SRS. Repeat SRS is a commonly employed treatment for incompletely obliterated AVMs. However, the relative efficacy of repeat versus initial SRS for AVMs has not been rigorously evaluated. In this retrospective, matched cohort study, we show that the outcomes after repeat SRS are significantly worse than after initial SRS for angioarchitecturally similar AVMs. While repeat SRS remains a viable treatment option for appropriately selected patients with incompletely obliterated AVMs, this potentially differential response to repeat versus initial SRS warrants further radiobiological analysis.

Learning Objectives: By the conclusion of this session, participants should be able to 1) Describe the importance of repeat SRS in the management AVMs, 2) Discuss, in small groups the outcomes after repeat compared to initial SRS for AVMs, and 3) Identify an effective treatment for incompletely obliterated AVMs after initial SRS.

References: 1. Awad AJ, Walcott BP, Stapleton CJ, Ding D, Lee CC, Loeffler JS. Repeat radiosurgery for cerebral arteriovenous malformations. J Clin Neurosci. Jun 2015;22(6):945-950. 2. Kano H, Kondziolka D, Flickinger JC, et al. Stereotactic radiosurgery for arteriovenous malformations, Part 3: outcome predictors and risks after repeat radiosurgery. J Neurosurg. Jan 2012;116(1):21-32. 3. Yen CP, Jain S, Haq IU, et al. Repeat gamma knife surgery for incompletely obliterated cerebral arteriovenous malformations. Neurosurgery. Jul 2010;67(1):55-64; discussion 64.