A single center, inter-observer evaluation of vestibular schwannoma stereotactic radiosurgery and its dosimetric impact.

The aim of this work was to evaluate the inter- and intra-observer variation in contouring vestibular schwannoma (VS) and the organs-at-risk (OAR), and its dosimetric impact in Volumetric Modulated Arc Therapy (VMAT). Three VS typical cases were contoured by four clinicians. The Agreement Volume Index (AVI) appeared to be notably higher in VS than in OARs, such that the dose coverage of VS is fairly robust. In OARs, the largest variation was +1.02Gy in dmax for the brainstem, +0.78Gy in dmean for the cochlea and +1.05Gy in dmax of the trigeminal nerve. Accordingly, it was decided that all VS delineations for stereotactic radiosurgery (SRS), and all frame-based SRS contouring in general, should always be reviewed by a second physician. In addition, the retrospective presentation of VS cases at daily peer review meetings has also been adopted to ensure that the consensus is constantly updated, as well as for training purposes.