Fractionated Proton Beam Therapy for Acoustic Neuromas: Tumor Control and Hearing Preservation.

Carolyn J Barnes,Lilia N Loredo,Roger I Grove,David A Bush,Jerry D Slater

doi:10.14338/ijpt-14-00014.1

Carolyn J Barnes, Lilia N Loredo + Show 3 more

Open Access

https://doi.org/10.14338/ijpt-14-00014.1

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Abstract

This prospective cohort evaluated patients with acoustic neuroma treated with proton irradiation at Loma Linda University Medical Center. A dose of 50.4 Gy in 28 fractions was given to improve hearing preservation while maintaining tumor control. Ninety-five patients were treated from March 1991 to March 2008. Fractionated proton radiotherapy at daily doses of 1.8 Gy was employed. Patients were treated to 1 of 3 total doses: 59.4 Gy, used initially for patients without serviceable hearing; 54 Gy, used for patients with serviceable hearing through October 2000; and 50.4 Gy used since 2001 for patients with serviceable hearing. Survival and local control were calculated using the Kaplan-Meier method. Logistic regression analysis was preformed comparing dose, tumor size, and tumor location with hearing preservation. Ninety-four patients were assessable; the median follow-up was 64 months. Five-year local control rates for the 59.4 Gy, 54 Gy, and 50.4 Gy groups were 95%, 97%, and 92%, respectively (P = .80); the overall 10-year actuarial control rate was 90%. Cranial nerve injuries occurred in <5% in all groups. Four-year actuarial rates of hearing preservation were maintained in 44% of patients treated with 54 Gy and 64% treated with 50.4 Gy (P = .284). On multivariate analysis, initial tumor diameter (≤1.5 cm) was found to be a prognostic factor for maintaining serviceable hearing in both groups (P = .011). Fractionated proton therapy of 50.4 Gy offers excellent local control and minimal cranial nerve toxicities. Improved rates of hearing preservation that are comparable with radiosurgery were seen with 50.4 Gy compared with higher doses, although this did not reach significance. Maintaining hearing was found to be associated with smaller initial tumor size.

Highlights

Acoustic neuromas are benign tumors that arise from the Schwann cells lining the VIIIth cranial nerve at the internal auditory meatus
This study examines patients treated with a decreased dose of 50.4 Gy in 28 fractions in an attempt to maximize serviceable hearing while still offering excellent tumor control rates
One patient died of a myocardial infarction 2 months after treatment and was deemed unassessable; another was lost to follow-up

Summary

Introduction

Acoustic neuromas (or vestibular schwannomas) are benign tumors that arise from the Schwann cells lining the VIIIth cranial nerve at the internal auditory meatus. The diagnosis is typically made with imaging techniques such as contrast-enhanced magnetic resonance imaging (MRI), and the use of this examination has been increasing. The increased use of MRI imaging has lead to an increase in diagnosis of smaller acoustic neuromas [1]. Surgical resection offers excellent local tumor control but has been associated with significant risk of injury to the Vth, VIIth, and VIIIth cranial nerves [3]. Stereotactic radiosurgery (SRS) has been used as a noninvasive approach for definitive treatment for small to medium-sized tumors as it offers excellent rates of local control and, with long-term follow-up, the range of hearing preservation from single-institution reports has been 32% to 71% [4]

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