Tumor Control And Hearing Outcome In A Series Of 185 Patients Treated By Gamma Knife Radiosurgery For Vestibular Schwannoma With A 12-gy Dose.

Keywords: gamma knife, hearing function, vestibular schwannoma, outcome, hearing preservation

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     Tumor control rate, hearing outcome and facial nerve function after Gamma Knife radiosurgery for vestibular schwannomas (VS) are varying between centers; the use of different dosimetric parameters or different technical methods could be the cause of these variations.
     We evaluate the tumor control rate and audiological status following Gamma Knife irradiation of VS using, for all patients, standardized dosimetric parameters and standardized methods of planification and irradiation.
     Over a 9-year period, we have treated 356 patients for a VS in our Gamma Knife center.
     We treated the patients using the following methodology: 1) tumor contouring using a combination of 3 imaging modalities (axial 1-mm sliced Gadolinium-enhanced T1-weighted, T2-weighted and CT densitometric 3D volume acquisitions); 2) dosimetric planning with 100% coverage; 3) prescription of a margin dose of 12-Gy at the 50% isodose; 3) irradiation with LGK-C with APS. All the patients were followed with serial audiograms, MRI and clinical evaluations after treatment; hearing status was classified using Gardner-Robertson classification; changes > 10% of the initial tumor volume were considered significant.
     A follow-up of minimum 2 years was available for 185 patients; 102 patients were treated less than 2 years ago, and 69 patients had an incomplete follow-up or a follow-up of less than 2 years. The mean follow-up duration was 3.8 years. Tumor control was achieved in 168 patients (91%). The Gardner-Robertson-related hearing status was unchanged for 139 patients (75%); functional hearing was maintained at last follow-up for 75% of the patients with useful hearing before treatment. No permanent facial palsy occurred.  
     This is a retrospective study.
     Using our methodology and dosimetric parameters, a tumor control rate > 90% with maintenance of same hearing status for 75% of the patients and no facial palsy could be achieved.


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