Irradiation of cochlear structures during vestibular schwannoma radiosurgery and associated hearing outcome

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The purpose of this study was to measure the dose of radiation delivered to the cochlea during a Gamma knife surgery (GKS) procedure for treatment of patients with vestibular schwannomas (VSs), and to analyze the relationship between cochlear irradiation and the hearing outcome of these patients.


Eighty-two patients with VSs were treated with GKS using a marginal dose of 12 Gy. No patient had neurofibromatosis Type 2 disease, and all had a Gardner–Robertson hearing class of I to IV before treatment, and a radiological and audiological follow-up of at least 1-year after GKS. The dosimetric data of the volume of the cochlea were retrospectively analyzed and were correlated with the auditory outcome of patients.


The mean radiation dose delivered to the cochlear volume ranged from 1.30 to 10.00 Gy (median 4.15 Gy). The cochlea received significantly higher radiation doses in patients with worsening of hearing after GKS. A highly significant association between the cochlear and the intracanalicular dose of radiation delivered during GKS was found.


During GKS for VSs, relatively high doses of radiation can be delivered to the cochlea. Worsening of hearing after GKS can be the consequence of either radiation injury to the cochlea or the irradiation dose delivered into the auditory canal, or both.

Abbreviations used in this paper:CT = computed tomography; GKS = Gamma knife surgery; IAC = internal auditory canal; MR = magnetic resonance; VS = vestibular schwannoma.

Article Information

Address correspondence to: Nicolas Massager, M.D., Gamma Knife Center, University Hospital Erasme, Route de Lennik 808, B-1070 Brussels, Belgium. email:

© AANS, except where prohibited by US copyright law.



  • View in gallery

    Axial CT scans (left), T1-weighted MR images after Gd (gad) administration (center), and T2-weighted MR images (right), showing the volume of the cochlea (Cochl; red line) drawn on the treatment plan. The blue line indicates tumor volume; yellow lines represent the 12-Gy isodose line; and the green lines indicate 8-, 5-, and 3-Gy isodose lines covering the cochlear volume.

  • View in gallery

    Dose–volume histograms of the cochlea for patients with hearing preservation and worsening of hearing after GKS. The cochlear volume of patients with audiological worsening after radiosurgery received a higher radiation dose than the dose received by the equivalent volume of the cochlea for patients with no hearing worsening.

  • View in gallery

    Scatterplot showing the statistical correlation between the mean radiation dose received by the cochlear volume and the integrated radiation dose to the intracanalicular part of the tumor.

  • View in gallery

    Graph showing the correlation between the percentage of filling of the VS into the IAC, the hearing outcome, and the mean radiation dose to the cochlea.


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