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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. [ABSTRACT FROM AUTHOR]

Background: Utilization of stereotactic radiosurgery (SRS) for brain metastases (BM) has become the technique of choice as opposed to whole brain radiation therapy (WBRT). The aim of this work is to evaluate the feasibility and potential benefits in terms of normal tissue (NT) and dose escalation of volumetric modulated arc therapy (VMAT) in SRS metastasis treatment. A VMAT optimization procedure has therefore been developed for internal dose scaling which minimizes planner dependence. Materials and methods: Five patient-plans incorporating treatment with frame-based SRS with dynamic conformal arc technique (DA) were re-planned for VMAT. The lesions selected were between 4-6 cm3. The same geometry used in the DA plans was maintained for the VMAT cases. A VMAT planning procedure was performed attempting to scale the dose in inner auxiliary volumes, and to explore the potential for dose scaling with this technique. Comparison of dose-volume histogram (DVH) parameters were obtained. Results: VMAT allows a superior NT sparing plus conformity and dose scaling using the auxiliary volumes. The VMAT results were significantly superior in NT sparing, improving both the V10 and V12 values in all cases, with a 2-3 cm3 saving. In addition, VMAT improves the dose coverage D95 by about 0.5 Gy. The objective of dose escalation was achieved with VMAT with an increment of the Dmean and the Dmedian of about 2 Gy. Conclusions: This work shows a benefit of VMAT in SRS treatment with significant NT sparing. A VMAT optimization procedure, based on auxiliary inner volumes, has been developed, enabling internal dose escalation. [ABSTRACT FROM AUTHOR]