Long-term follow-up studies of Gamma Knife surgery with a low margin dose for vestibular schwannoma

Abstract

The aim of this study was to assess long-term clinical outcomes in patients who underwent Gamma Knife surgery (GKS) with a low margin dose-14 Gy or less-to treat vestibular schwannoma (VS) unrelated to neurofibromatosis Type II. Between December 1994 and December 2001, 200 patients with VSs underwent GKS, which was performed using the Leksell Gamma Knife model B. More than 10 years of follow-up is available in these patients. One hundred ninety patients (88 male and 102 female patients) were followed up using MRI (follow-up rate 95%). The mean age of these patients was 50.6 years (range 10-77 years). Gamma Knife surgery was the primary treatment for VS in 134 cases (70.5%) and was an adjunctive management approach in 56 cases (29.5%). The median tumor margin dose was 13.0 Gy (range 6.0-14.4 Gy), and the median maximum tumor dose was 28.0 Gy (range 15.0-60.0 Gy). The median tumor volume was 3.6 cm(3) (range 0.3-27.3 cm(3)). The median duration of follow-up in these patients was 109 months (range 8-195 months). In the 190 patients, the latest follow-up MRI studies demonstrated tumor regression in 122 patients (64.2%), stable tumor in 48 patients (25.3%), and tumor enlargement in 20 patients (10.5%). The total rate of tumor control was 89.5%. Using the Kaplan-Meier method, the authors found the estimated 3-, 5-, 10-, and 15-year tumor control rates to be 95%, 93%, 86%, and 79%, respectively; and the estimated 3-, 5-, and 10-year hearing preservation rates to be 96%, 92%, and 70%, respectively. Twenty-six patients (13.7%) exhibited transient mild facial palsy or facial spasm, and 2 patients (1.1%) suffered persistent mild facial palsy. Thirty-nine patients (20.5%) had transient trigeminal neuropathy, and 5 patients (2.6%) suffered from persistent mild facial numbness. The incidence of persistent severe facial and trigeminal neuropathy was 0.0%. With a low prescribed margin dose of 14 Gy or less, GKS was confirmed to provide long-term tumor control for small to medium-sized VSs and largely to prevent cranial nerves from iatrogenic injury. Based on the findings of this study, GKS is also a reasonable option for the treatment of large, heterogeneously enhancing tumors without symptomatic brainstem compression. Gamma Knife surgery can preserve a high quality of life for most patients with VS who do not have symptomatic brainstem compression. Long-term follow-up is required because of the risk of delayed recurrence of VS.