Vol.:(0123456789) 1 3 International Journal of Clinical Oncology https://doi.org/10.1007/s10147-018-1267-6 ORIGINAL ARTICLE Five‑year outcomes following hypofractionated stereotactic radiotherapy delivered in fve fractions for acoustic neuromas: the mean cochlear dose may impact hearing preservation Zhiping Chen 1  · Keiichi Takehana 1  · Takashi Mizowaki 1  · Megumi Uto 1  · Kengo Ogura 1  · Katsuyuki Sakanaka 1  · Yoshiki Arakawa 2  · Yohei Mineharu 2  · Yuki Miyabe 1  · Nobutaka Mukumoto 1  · Susumu Miyamoto 2  · Masahiro Hiraoka 1 Received: 27 December 2017 / Accepted: 14 March 2018 © Japan Society of Clinical Oncology 2018 Abstract Background The aim of this study was to assess the clinical outcomes of acoustic neuromas (ANs) treated with hypofrac- tionated stereotactic radiotherapy (hypo-FSRT) prescribed at a uniform dose. Methods 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 fve fractions per week to the isocenter, and the planning target volume was covered by the 80% isodose line. Results 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 signifcantly 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 signifcant diference was identifed in the mean biological efective dose with an α/β value of 3 Gy (BED 3 ) to the ipsilateral cochlea between the preserved hearing and hearing loss groups (19 Gy vs. 28 Gy) (p = 0.08). Conclusions Hypo-FSRT delivered in fve fractions for unilateral ANs may achieve excellent tumor control with no severe facial or trigeminal complications. The mean BED 3 in the cochlea may impact the hearing preservation rate. Therefore, the cochlear dose should be as low as possible. Keywords Acoustic neuroma · Stereotactic irradiation · Radiotherapy · Hypofractionation · Hearing preservation Introduction Acoustic neuromas (ANs) belong to a group of benign tumors that pathophysiologically arise from vestibular nerves and clinically present with initial symptoms of hear- ing loss, tinnitus, vertigo, and/or dizziness that may worsen gradually as the tumor enlarges. Following tumor expansion beyond the internal acoustic meatus and tumor compres- sion to the brainstem and fourth ventricle, severe symptoms such as trigeminal nerve dysesthesia, facial nerve paralysis, cerebellar ataxia, and intracranial hypertension may occur, and such symptoms could vastly afect the patient’s quality of life and ultimately threaten his/her life [1]. To date, treatment options for ANs have been comprised of wait-and-scan microsurgery, stereotactic radiosurgery (SRS) and fractionated stereotactic radiotherapy (FSRT). The best treatment option should be decided upon based on the patient’s background, such as age, comorbidities, tumor size, symptoms, and individual preference, and should be routinely made following agreement among a multidiscipli- nary team consisting of neurosurgeons, radiation oncolo- gists, speech and language therapists, and neuroradiologists [2]. Current data of Gamma Knife ® surgery (GKS) supports * Takashi Mizowaki mizo@kuhp.kyoto-u.ac.jp 1 Department of Radiation Oncology and Image-Applied Therapy, Graduate School of Medicine, Kyoto University, 54 Shogoin Kawahara-cho, Sakyo-ku, Kyoto 606-8507, Japan 2 Department of Neurosurgery, Graduate School of Medicine, Kyoto University, 54 Shogoin Kawahara-cho, Sakyo-ku, Kyoto 606-8507, Japan