Room: AAPM ePoster Library
Purpose: integrated SBRT/IMRT treatment system is available clinically that combines a Gamma ray head for intra- and extra-cranial SRS/SBRT and a 6MV linac head for conventional radiotherapy and IMRT/VMAT on the same rotating gantry. This study investigates the dosimetric quality of treatment plans for the new treatment system by comparing treatment plans for patients previously treated on Varian accelerators.
Methods: Panther TPS (version 5.60.4657, Prowess Inc., Concord, CA) was commissioned for the new machine in this retrospective study. Twenty previous SBRT/IMRT patients were unachieved from our clinical database, who were planned using Varian Eclipse TPS and treated on Varian accelerators (Varian Medical Systems, Palo Alto, CA). Treatment sites included head and neck, lung and liver. Matching optimization parameters and beam configuration were used in the re-planning process. Plan quality was evaluated using the homogeneity index, conformity index, Dmax, Dmin, Dmean, and Dmax and Dmean for organs at risk (OAR).
Results: Panther TPS produced clinical acceptable treatment plans for the new treatment system. For the same PTV coverage (Dp assigned to 95% isodose line), the mean HI and CI was 0.11±0.01 and 0.79±0.02 for Panther plans and 0.08±0.01 and 0.82±0.02 for Eclipse plans, respectively, and Dmean was within 2% between the two treatment systems. For plans of comparable quality, Panther/direct-aperture optimization (DAO) required less MLC segments and MUs compared with Eclipse/beamlet-based optimization. When target and OARs were in close proximity, DAO resulted in less homogeneous target dose (i.e., up to 5% higher Dmax). Generally, Panther DAO optimization took marginally longer computing time than the Varian Eclipse system.
Conclusion: study showed that the Prowess TPS produced clinically acceptable treatment plans for the new machine comparable to the previously treated Varian Eclipse plans in terms of target coverage, conformity index and OAR sparing.