Fractionated Stereotactic Radiation Therapy for Large Vestibular Schwannomas

Abstract

Fractionated stereotactic radiotherapy (FSRT) is a well-established and effective treatment for vestibular schwannomas (VS). For larger VSs with brainstem compression, debulking surgery is often performed prior to radiation to reduce treatment volume and to decrease potential radiation damage to the brainstem and cranial nerves V and VII. The goal of this study was to retrospectively evaluate the clinical outcomes of patients with large VSs treated with FSRT at our institution. 60 patients were identified who had VSs treated with FSRT between 2009 and 2016. All patients were treated on a Novalis TX linear accelerator platform with a dose of 25 Gy in 5 fractions. Patients were categorized by Koos stage into small VS group (Koos stage 1 or 2) and large VS group (Koos stage 3 or 4). Outcomes of tumor control (freedom from radiographic progression), degree of trigeminal nerve dysfunction, degree of facial nerve dysfunction (using the House-Brackmann scale), and brainstem toxicity (radiographic necrosis) were assessed prior to treatment and at the most recent follow-up. The dose of radiation to the VS, cranial nerves, and brainstem (Dmax, D0.5cc, and V23) were evaluated in order to identify correlated late toxicity. The number of patients experiencing symptomatic pseudoprogression at any point post treatment was also recorded for each group. Clinical and radiographic data was available for 59 of the patients, and median follow-up was 33.5 months for the small VS group (range 5 – 76 months) and 15 months for the large VS group (range 2 – 49 months). The median treated volume for the small VS group was 0.9 cc (range 0.1 – 3.4 cc) and 5.2 cc for the large VS group (range 1.4 – 22.6 cc). The median brainstem Dmax was 16.5 Gy for the small VS group (range 1.1 – 28.4 Gy) and 26.1 Gy for the large VS group (range 21.7 – 30.4 Gy). The median D0.5cc was 4.75 Gy for the small VS group (range 0 – 21.7 Gy) and 20.5 Gy for the large VS group (range 9 – 23.8 Gy). The median V23 was 0.18 cc for the small VS group (range 0 – 0.33 cc) and 0.18 cc for the large group (0 – 0.62 cc). Tumor control was 100% in both groups, and there was no evidence of brainstem necrosis in either group. No patients experienced progression of trigeminal symptoms. Freedom from new facial neuropathy was 97.6% in the small VS group vs. 100% in the large VS group (p=0.99). Rates of pseudoprogression were 4.8% in the small VS group vs. 11.8% in the large group (p=0.13). Debulking surgery was performed in 2 of 42 patients in the small VS group and in 10 of 18 patients in the large VS group and was not found to affect any of these clinical outcomes. Patients with large VSs or with brainstem compression did not experience worse rates of tumor control, brainstem necrosis, pseudoprogression, or neuropathy compared to those with small VSs. Outcomes were similar for those treated with or without surgery, suggesting that FSR alone is a reasonable treatment option for patients with large VSs compressing the brainstem.