The Barrow Neurological Institute Experience with stereotactic radiosurgery for vestibular schwannomas: single vs. multiple fraction and hearing outcomes.

Keywords: vestibular schwannoma, gamma knife, outcome, cyberknife, fractionated stereotactic radiotherapy

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     Vestibular schwannomas (VS) are benign tumors of the cerebellopontine angle. Their treatment has evolved with radiosurgery playing an increasing role. As such, an emphasis on cranial nerve preservation has been pursued. Hearing preservation rates have historically ranged from 40-90% at 3 years. Fractionation has been an important treatment strategy to preserve other cranial nerve function such as the optic nerve. Therefore, fractionated radiosurgery has been suggested as a treatment strategy to preserve hearing in patients with VS.
     We sought to compare the single fraction (SFRS) with hypo-fractionated radiosurgery (HFRS) at a single institution with respect to hearing outcomes in patients with acoustic neuromas.
     We treated 386 patients with vestibular schwannomas. We excluded those patients with less than six months of follow-up, those with NF2 and those without both pre- and post-treatment audiograms. The study sample consisted of 210 patients: 94 HFRS and 116 SFRS. Mean age was 55 years for HFRS and 62 years for SFRS (p =0.001).
     VS treated with stereotactic radiosurgery (SRS) using either SFRS or HFRS from 1997 through 2011 at the Barrow Neurological Institute. All GammaKnife patients were treated with SFRS, and most Cyber Knife patients were treated with HFRS.
       Statistical significance was found between groups with the SFRS group being older. Prior resection occurred in 19.8% of the HFRS group and 29.3% of SFRS group (p=0 .129). Mean tumor volume (cc) in HFRS was 2.78 and SFRS of 2.28 (p=0.222). At last follow-up, hearing was preserved in 38% of SFRS and 61% HFRS (p=0 .019). The hearing preservation rate was higher in those with AAO grade A prior to SRS; 52% of SFRS and 74% of HFRS subjects (p=0.161). Tumor volume had no impact on hearing preservation (p= 0.154). Resection-free tumor control was found in 97.7% of HFRS subjects and 98.4% of SFRS subjects. Regression analysis found HFRS statistically significant in hearing preservation (p= 0.004, OR 4.426, 95% CI, 1.587-12.347).
     This was a retrospective comparison study.
     HFRS appears to have superior outcomes compared with SFRS with respect to hearing outcomes when VS are treated with stereotactic radiosurgery.
     A prospective study of is warranted.


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