Stereotactic Radiosurgery for Neurofibromatosis 2-Associated Vestibular Schwannomas: Toward Dose Optimization for Tumor Control and Functional Outcomes

BACKGROUND: Management of neurofibromatosis type 2 (NF2)-associated vestibular schwannomas (VSs) remains controversial. Stereotactic radiosurgery (SRS) with conventional dosing is less effective for NF2-related VS compared with sporadic lesions. OBJECTIVE: To evaluate optimal SRS dose parameters for NF2-related VS and to report long-term outcomes. METHODS: A prospective database was reviewed and outcome measures, including radiographic progression, American Academy of Otolaryngology-Head and Neck Surgery hearing class, and facial nerve function, were analyzed. Progression-free survival was estimated with Kaplan-Meier methods. Associations between tumor progression and radiosurgical treatment parameters, tumor volume, and patient age were explored with the use of Cox proportional hazards regression. RESULTS: Between 1990 and 2010, 26 patients with 32 NF2-related VSs underwent SRS. Median marginal dose and tumor volume were 14 Gy and 2.7 cm(3), respectively. Twentyseven tumors (84%) showed no growth (median follow-up, 7.6 years). Kaplan-Meier estimates for 5- and 10-year progression-free survival were 85% and 80%, respectively. Cox proportional hazards demonstrated a significant inverse association between higher marginal doses and tumor progression (hazard ratio, 0.49; 95% confidence interval, 0.170.92; P = .02). Audiometric data were available in 30 ears, with 12 having class A/B hearing before SRS. Only 3 maintained serviceable hearing at the last follow-up. Four underwent cochlear implantation. Initially, 3 achieved open-set speech recognition, although only 1 experienced long-term benefit. Facial nerve function remained stable in 50% of cases. CONCLUSION: Higher marginal doses than commonly prescribed for sporadic VS were associated with improved tumor control in patients with NF2. Hearing outcomes were poor even when contemporary reduced marginal doses were used. However, SRS allows an anatomically preserved cochlear nerve and may permit hearing rehabilitation with cochlear implantation. Further consideration should be given to optimum dosing to achieve long-term control while maximizing functional outcomes.