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Abstract: Purpose: The purpose with this study was to compare multi-criteria optimization (MCO) for volumetric modulated arc therapy (VMAT) treatment plans in two different treatment planning systems. Theory: When performing treatment planning prior to radiation therapy it is important to prioritize between absorbed dose to target and absorbed dose to organs at risk (OAR). A treatment plan where one treatment goal cannot be improved without impairing another treatment goal is called a Pareto optimal plan. MCO has been proposed as an alternative optimization method for VMAT treatment plans, which will provide several solutions of alternative treatment plans that is at, or close to the Pareto front. The treatment planning systemwill make it possible for the user to navigate between the possible solutions that the optimization has created and choose the plan that best fulfils the treatment planning goals.Method: Five patients with prostate cancer and five patients with head and neck (H&N) tonsil cancer have been anonymously selected consecutively from the clinical database at Sahlgrenska University Hospital. New VMAT treatment plans were made with MCO in Eclipse (Varian Medical Systems) and RayStation (RaySearch Laboratories). The aim was to give both treatment planning systems (TPS) the same conditions in order to compare the plans fairly. The MCO created Pareto plans and generated a slider for each objective selected. The sliders were thereafter moved to reduce the dose to the organs at risk as much as possible, but at the same time maintain the target dose coverage. Evaluation of the treatment plans was made by evaluating chosen points in the calculated dose-volume histogram but also by evaluating conformity index, heterogeneity index and the complexity of the treatment plans. Result:Conclusion: Dosimetrically, treatment plans created in Eclipse MCO usually provided lower values to the OARs than the treatment plans created in RayStation MCO, but after post processing, RayStation usually provided lower values to the OARs than the treatment plans created in Eclipse MCO. The mean value of the conformity index for Eclipse MCO and RayStation MCO with post processing was 0.9 and 0.78 respectively for the prostate cases and 0.87 and 0.81 respectively for the H&N cases. The values for the heterogeneity index were similar in both TPSs. The calculated complexity index was, in most cases, similar for the prostate cases, however the treatment plans for the H&N cases created in RayStation had generally a lower value of complexity than those created in Eclipse. MCO has proven to be a useful tool for VMAT treatment planning. The management procedure differed for the two TPSs, however, it was in most cases dosimetrically possible to achieve the same treatment planning goals.

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