(Sunday, 7/14/2019)
Room: ePoster Forums
Purpose: Treatment planning of SRS with multiple metastases usually mandates separate plan per lesion which results into much longer treatment time due to multi-isocenter setup using dynamic conformal arc therapy (DCAT). The aim of this study is to investigate the benefits of treating multiple brain metastases using single-isocenter volumetric modulated arc therapy (VMAT) over conventional multi-isocenter DCAT.
Methods: VMAT plans were retrospectively generated for 9 patients with 2 to 6 brain mets who were previously treated to 20Gy using DCAT on Novalis Txâ„¢ system. The DCAT and VMAT plans were planned using Brainlab iPlan v4.5 and Varian Eclipse v11.0 TPS respectively. Number of isocenters in every DCAT plan were equal to the number of metastases. However, with VMAT plans, the individual PTVs were combined to form a single PTV and plans were done with one isocenter, which was at the centroid of the combined PTV. The single-isocenter VMAT plans had 4 arcs, out of which two of them were non-coplanar. DCAT plans were delivered with a dose rate of 1000 MU/min and VMAT plans could be delivered with a maximum dose rate of 600 MU/min. For comparison, target coverage and dose to OARs (i.e. brain V12Gy, brainstem, optic apparatus, etc) were recorded for both plan types.
Results: VMAT has potential advantage for the patients with more than 3 metastases. In those patients, the treatment time is shorter for VMAT plans which helps completing the treatment faster thereby reducing patient motion and discomfort during treatment. In addition, the conformity index is better for VMAT plans than that of DCAT plans for patients with more than 3 metastases. The other OAR doses were very similar between both the techniques.
Conclusion: VMAT plans offer significant advantage over DCAT plans with lesser overall treatment time and better conformity index and comparable OAR sparing.
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