Objectives: Large vestibular schwannoma (VS) presenting with highly symptomatic mass effect and brainstem compression may represent a more biologically aggressive entity than incidentally diagnosed or indolent VS. Progression following subtotal or near-total resection of this subset of VS is common, and local control after salvage stereotactic radiosurgery (SRS) using standard doses of 12-13 Gy is poor. We hypothesized that dose-escalated SRS, corrected for biologically effective dose, would have superior local control of high-grade VS progressing after subtotal or near-total resection compared to standard-dose SRS.

Methods: After IRB approval, we performed a retrospective cohort study of adult patients treated at our institution with linear accelerator-based SRS for progressive VS following subtotal or near-total resection. Dose-escalated SRS was defined by a biologically effective dose exceeding a single-fraction 13 Gy regimen. Study outcomes were local control and neurologic sequelae of SRS. Binary logistic regression and Cox proportional hazards regression evaluated predictors of study outcomes.

Results: A total of 18 patients with progressive disease following subtotal (71%) and near-total (39%) resection of Koos grade IV disease (94%) were enrolled. Seven patients were treated with dose-escalated SRS, and eleven patients were treated with standard-dose SRS. Over a median follow-up of 32 months after SRS, local control was 100% in the dose-escalated cohort and 91% in the standard-dose cohort. Transient and late neurologic sequelae occurred in 28% of patients, the most common being transient facial nerve neuropathy. One patient in the dose-escalated cohort developed a malignant peripheral nerve sheath sarcoma 15 years following SRS. A greater number of toxicities occurred in the dose-escalation cohort though this was not significant (p=0.1204).

Conclusions: Dose-escalated SRS appears to offer improved local control of recurrent VS following progression after subtotal or near-total resection, although dose-escalated SRS may be associated with worsened transient neurologic toxicity compared to standard-dose SRS. Future well-powered prospective studies of dose-escalated SRS for progressive VS with macroscopic residual disease following microsurgery are warranted.