Dosimetric Comparison of Dynamic Trajectory Radiotherapy, HyperArc and VMAT Treatment Plans

Recently we developed a new radiotherapy technique called dynamic trajectory radiotherapy (DTRT), which additionally to VMAT includes dynamic table and collimator rotations during beam on to further increase degrees of freedom for the selection of beam directions. In this work, achievable dose distributions for DTRT will be compared to currently available arc delivery techniques like HyperArc and VMAT. In this study ten clinically motivated cases – including five brain, two head and neck, two lung and one prostate – were considered. Organs at risk (OARs) structures as well as the target were contoured according to the treatment site. A dedicated framework utilizing the Eclipse Scripting Research API was used to determine gantry-table and gantry-collimator paths based on contoured structures overlapping with the target by means of an A* path searching algorithm for non-coplanar beam directions. These paths served as input for the intensity optimization using a research version of the VMAT optimization algorithm in Eclipse leading to a DTRT treatment plan for all cases. Additionally, a HyperArc treatment plan was generated for each brain case. For the remaining cases VMAT treatment plans for an o-ring linear accelerator were created. Resulting dose distributions for DTRT were compared with HyperArc and VMAT plans based on DVH parameters. The deliverability of DTRT treatment plans on a linear accelerator were assessed by comparing measured dose distributions using either gafchromic films or the Delta4 system and the corresponding calculated dose distributions. For all cases considered, the DVHs for the target show a similar dose coverage for all delivery techniques. On average the mean doses for parallel OARs and near maximum doses for serial OARs were reduced for DTRT treatment plans by about 14% ± 1% and 17% ± 2%, respectively, when compared with HyperArc treatment plans. The analogous comparison between DTRT and VMAT plans result in improvements for DTRT of about 22% ± 2% and 19%± 5%, respectively. Measured and calculated dose distributions show on average a gamma passing rate >98% for global 3%/2 mm criteria and a threshold of 10%. DTRT treatment plans perform better or similar compared to HyperArc or Halcyon VMAT plans, depending on the case and on the OAR considered. The improvement of DTRT plans is more pronounced when compared with Halcyon VMAT treatment plans than with HyperArc plans. The results demonstrate that DTRT has a great potential to reduce dose to OARs, while target coverage is preserved when compared with currently clinically applied arc delivery methods.