Five-year outcomes following hypofractionated stereotactic radiotherapy delivered in five fractions for acoustic neuromas: the mean cochlear dose may impact hearing preservation

The aim of this study was to assess the clinical outcomes of acoustic neuromas (ANs) treated with hypofractionated stereotactic radiotherapy (hypo-FSRT) prescribed at a uniform dose. Forty-seven patients with a unilateral AN were treated consecutively with hypo-FSRT between February 2007 and March 2012. Nineteen patients maintained a serviceable hearing status at the beginning of hypo-FSRT. The prescribed dose was 25 Gy delivered in five fractions per week to the isocenter, and the planning target volume was covered by the 80% isodose line. The median follow-up and audiometric follow-up periods were 61 and 52 months, respectively. The estimated tumor control rate at 5 years was 90% (95% CI 76–96). The existence of the cystic component before hypo-FSRT had a significantly worse impact on tumor control (p = 0.02). The estimated hearing preservation rates at 1, 3 and 5 years were 68% (95% CI 42–84), 41% (95% CI 20–62) and 36% (95% CI 15–57), respectively. A borderline significant difference was identified in the mean biological effective dose with an α/β value of 3 Gy (BED3) to the ipsilateral cochlea between the preserved hearing and hearing loss groups (19 Gy vs. 28 Gy) (p = 0.08). Hypo-FSRT delivered in five fractions for unilateral ANs may achieve excellent tumor control with no severe facial or trigeminal complications. The mean BED3 in the cochlea may impact the hearing preservation rate. Therefore, the cochlear dose should be as low as possible.