Fractionated Proton Radiation Therapy and Hearing Preservation for Vestibular Schwannoma: Preliminary Analysis of a Prospective Phase 2 Clinical Trial

Abstract

Background: Local management for vestibular schwannoma (VS) is associated with excellent local control with focus on preserving long-term serviceable hearing. Fractionated proton radiation therapy (FPRT) may be associated with greater hearing preservation because of unique dosimetric properties of proton radiotherapy.

Objective: To investigate hearing preservation rates of FPRT in adults with VS and secondarily assess local control and treatment-related toxicity.

Methods: A prospective, single-arm, phase 2 clinical trial was conducted of patients with VS from 2010 to 2019. All patients had serviceable hearing at baseline and received FPRT to a total dose of 50.4 to 54 Gy relative biological effectiveness (RBE) over 28 to 30 fractions. Serviceable hearing preservation was defined as a Gardner-Robertson score of 1 to 2, measured by a pure tone average (PTA) of ≤50 dB and a word recognition score (WRS) of ≥50%.

Results: Twenty patients had a median follow-up of 4.0 years (range 1.0-5.0 years). Local control at 4 years was 100%. Serviceable hearing preservation at 1 year was 53% (95% CI 29%-76%), and primary end point was not yet reached. Median PTA and median WRS both worsened 1 year after FPRT (P < .0001). WRS plateaued after 6 months, whereas PTA continued to worsen up to 1 year after FPRT. Median cochlea D90 was lower in patients with serviceable hearing at 1 year (40.6 Gy [RBE] vs 46.9 Gy [RBE]), trending toward Wilcoxon rank-sum test statistical significance (P = .0863). Treatment was well-tolerated, with one grade 1 cranial nerve V dysfunction and no grade 2+ cranial nerve dysfunction.

Conclusion: FPRT for VS did not meet the goal of serviceable hearing preservation. Higher cochlea doses trended to worsening hearing preservation, suggesting that dose to cochlea correlates with hearing preservation independent of treatment modality.

Trial registration: ClinicalTrials.gov NCT01199978.

Copyright © Congress of Neurological Surgeons 2022. All rights reserved.

Figures

FIGURE 1.

Fractionated proton therapy plan for vestibular schwannoma with 3 noncoplanar fields. Dose distribution is visualized from a 3-field plan, revealing the 95%, 50%, and 20% isodose lines. Planning target volume, brainstem, and cochlea are outlined, showing excellent conformity of the Planning Target Volume and significant overlap of the adjacent cochlea.

FIGURE 2.

Hearing outcomes over time. A, Serviceable hearing before and after RT, B, distribution of ipsilateral PTA before and after RT, and C, distribution of the ipsilateral word recognition score before and after RT. Box plots depict the horizontal line representing median values, and lower and upper boundaries indicated the 25th and 75th percentiles, respectively, with outliers representing minimum and maximum values. PTA, pure tone average; RT, radiation therapy.

FIGURE 3.

Individual and median hearing outcomes, A, ipsilateral Gardner–Robertson scores before and after RT, B, ipsilateral PTA before and after RT, and C, ipsilateral word recognition score before and after RT. PTA, pure tone average; RT, radiation therapy.