Long-Term Outcomes for Nonacoustic Schwannomas Treated with Stereotactic Radiation Therapy

Background: Nonacoustic schwannomas (NACS) are rare tumors that are commonly treated with radiation therapy (XRT) due to their location not being amenable to optimal resection. We investigated the long-term outcomes of NACS treated with XRT.

Materials and Methods: We conducted a retrospective review of patients with NACS treated with fractionated stereotactic radiation therapy (FSRT) or Gamma Knife (GK-SRS) from 1996 to 2017 at our institution. We examined patient demographics, cranial nerve (CN) involvement, CN function pre-/post-XRT, treatment volume (TV), toxicity, surgery pre-/post-XRT, progression free survival (PFS), and overall survival (OS). Kaplan–Meier analysis was performed for survival measures.

Results: We identified 63 patients (28 males, 38 females). Forty-eight patients (72.7%) were treated with FSRT (median dose: 50.4 Gy in 1.8 Gy/fraction; range: 45–54 Gy), and 18 (27.3%) with GK-SRS (median dose: 12 Gy; range: 12–15 Gy). Median follow-up time was 71.4 months (5–240). Median KPS was 90 (70–100). Median age at XRT was 45 years old (15–92). Prior to XRT, 28.6% patients had surgical resection, with median time from surgery to XRT of 8 months (0.5–130 months). Median treatment volume was 4.72 mL (0.26–29). CN involvement was most common with CN5 (42.9%), followed by CN10 (15.9%), and the rest with CN7 (12.7%), CN12 (7.9%), CN3 (3 patients) CN4 (4) CN6 (4), CN9 (3), and one cavernous sinus. Post-XRT, CN function improved in most patients (51.8%), remained stable in 39.2%, and worsened in 8.9%. Local control at 1 and 5 years was 100%. Recurrence rate was observed in 2 patients (3.2%), one at 9 years and one at 14 years, post-XRT. OS at 1, 5, and 10 years was 100, 98.1, and 92%, respectively. PFS at 1, 5, and 10 years was 100, 98.1, and 85.8%, respectively.

Conclusion: NACS have great outcomes for preserving and/or improving CN function with excellent local control and survival when treated with FSRT or GK-SRS.