IMRT quality assurance using a second treatment planning system

Abstract

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 computed tomography scan of our QA phantom that consists of three Solid Water slabs sandwiching radiochromic films, and an ion chamber that is inserted into the center slab of the phantom. For the independent verification, the dose was recalculated using the Varian Eclipse TPS using the multileaf collimator files and beam geometry from the original plan. The data was then compared in terms of absolute dose to the ion chamber volume as well as relative dose on isodoses calculated at the film plane. The calculation results were also compared with measurements performed for each case. When comparing ion chamber doses, the mean ratio was 0.999 (SD 0.010) for Eclipse vs. Corvus, 0.988 (SD 0.020) for the ionization chamber measurements vs. Corvus, and 0.989 (SD 0.017) for the ionization chamber measurements vs. 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 vs. Corvus, 85.1 (SD 10.6) for Corvus vs. film, and 93.7 (SD 4.1) for Eclipse vs. film; and for the criteria of 5%, 3 mm, 98.7 (SD 1.5) for Eclipse vs. Corvus, 93.0 (SD 7.8) for Corvus vs. film, and 98.0 (SD 1.9) for Eclipse vs. film. We feel that the use of the Eclipse TPS as an independent, accurate, robust, and time-efficient method for patient-specific IMRT QA is feasible in clinic.