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In this study, we used a second treatment planning system (TPS) for independent verification of the dose calculated by our primary TPS in the context of patient specific quality assurance (QA) for intensity modulated radiation therapy(IMRT). QA plans for 24 patients treated with inverse planned dynamic IMRT were generated using the Nomos Corvus TPS. The plans were calculated on a CT scan of our QA phantom that consists of three Solid Water slabs sandwiching radiochromic films, and an ion chamber inserted into the center slab. For the independent verification, the dose was recalculated using the Varian Eclipse TPS from the original plan. The absolute dose to the ion chamber volume was then compared, as well as relative dose on isodoses calculated at the film plane. The calculation results were also compared to measurements. For point doses the mean ratio was 0.999 (SD 0.010) for Eclipse versus Corvus, 0.988 (SD 0.020) for the chamber measurements versus Corvus, and 0.989 (SD 0.017) for the chamber measurements versus Eclipse. For 2D doses with gamma histogram the mean value of the percentage of pixels passing the criteria of 3%, 3 mm was 94.4 (SD 5.3) for Eclipse versus Corvus, 85.1 (SD 10.6) for Corvus versus film, and 93.7 (SD 4.1) for Eclipse versus film. We feel that it is feasible to use the Eclipse TPS as an independent, accurate, and time efficient method for dose calculations verifications IMRT QA in clinic. |
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