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Treatment Outcomes in Patients Treated With CyberKnife Radiosurgery for Vestibular Schwannoma

Objective To evaluate tumor control, hearing, tinnitus, and balance outcomes of patients treated with CyberKnife (CK) radiosurgery for vestibular schwannoma (VS). Study Design Retrospective series review. Setting Tertiary referral center. Patients All patients treated with CK radiosurgery for vestibular schwannoma by a multidisciplinary radiosurgical team from August 2005 to November 2011. The median age was 59 years, and mean follow-up was 40 months. Seventy-three patients were treated (63 primary radiosurgery and 10 postsurgical). Interventions CK radiosurgery, serial MRI imaging, comprehensive audiometry, Tinnitus Handicap Inventory (THI) scores, and Activities-Specific Balance Confidence Scale (ABC). Main Outcome Measures Tumor control defined as 2 mm linear growth or lower or less than 20% increase in tumor volume (TV), measured in cubic centimeter, after a minimum of 12 months of monitoring, audiogram profiles, THI, and ABC surveys. Results Of those treated with CK as primary modality, 83% had 0- to 2-mm growth (tumor control or stable) and 17% grew greater than 2 mm. Of the tumors that were stable, 29% shrank 2 mm or greater. Volumetric analysis found that 74% of tumors had less than 20% TV growth, whereas 26% exhibited 20% or greater increase in TV. Of those deemed stable, 65% shrank 20% or greater TV; 95% of patients did not need additional surgical intervention, 3 required salvage surgery and 1 underwent additional radiosurgery. The majority of patients started with Class D hearing, but of those with Class A or B hearing before treatment, 53.5% maintained serviceable hearing at 3 years of follow-up. The pretreatment and posttreatment median THI Grades were both 1. The pretreatment and posttreatment ABC scores were unchanged at 81%. Conclusion The LINAC-based CK (18 Gy over 3 fractions at 80% isodose line) provides tumor control rates comparable to other forms of radiosurgery. Analysis for tumor growth was positive for 17% using maximum linear diameters and 26% with a volumetric workstation. This discrepancy is consistent with previous reports where volumetric models were found to be more sensitive in establishing growth. Serviceable hearing was comparable to previous SRS and SRT reports with an overall hearing preservation of 53.5%. This number was 77% in those with pre-Class A hearing. SRS did not affect pretreatment tinnitus or vestibular function.