Long-term Outcomes of Gamma Knife Radiosurgery for Treating Vestibular Schwannoma With a Lower Prescription Dose of 12 Gy Compared With Higher Dose Treatment

Objective: Gamma knife radiosurgery (GKRS) is commonly used to treat vestibular schwannomas (VSs). The risk of complications from GKRS decreases at lower doses, but it is unknown if long-term tumor control is negatively affected by dose reduction. Study Design: This was a retrospective case review and analysis of patient data. Setting: Tertiary referral center. Patients: Patients with VSs who underwent GKRS between 1990 and 2007 at the authors' institution. Intervention(s): The subjects were divided into two cohorts based on the prescribed doses of radiation received: a 12 Gy cohort (96 patients) with a follow-up period of 124 months and a >12 Gy cohort (118 patients) with a follow-up period of 143 months. Main Outcome Measures: Tumor control rates at 10 to 15 years, frequency of facial and trigeminal nerve complications, and hearing function. Results: The 10 to 15-year tumor control rates were 95% in the 12 Gy cohort and 88% in the > 12 Gy cohort, but the differences were not significant. Compared with the >12 Gy cohort, facial and trigeminal nerve deficits occurred significantly less frequently in the 12 Gy cohort, with the 10-year cumulative, permanent deficit-free rates being 2% and 0%, respectively. Multivariate analyses revealed that treatment doses exceeding 12 Gy were associated with a significantly higher risk for cranial nerve deficits. The percentage of subjects retaining pure-tone average <= 50 dB at the final follow-up did not significantly differ between the cohorts (12 Gy cohort, 30% and >12 Gy cohort, 33%; p = 0.823). Conclusions: Dose reduction to 12 Gy for GKRS to treat VSs decreased facial and trigeminal nerve complications without worsening tumor control rates.