SU-E-T-614: A Comparison of IMRT Plans for the ViewRay MR-Guided RT System with TomoTherapy and Pinnacle.
PURPOSE
To begin to assess the treatment planning capabilities of the ViewRay MR-guided radiotherapy system.


METHODS
Treatment plans created using ViewRay software were compared with previously completed Pinnacle and TomoTherapy plans from patients in our clinic. Sites such as pancreas were chosen due to the soft-tissue contrast which makes them candidates for MR-image guidance with ViewRay. CT images and structure sets were exported from their original planning systems and imported into ViewRay. MR images were not the focus of this investigation since we required a direct comparison with existing plans utilizing CT. ViewRay plans were created as equivalently as possible with the original planning environment, matching prescription and normal structure priorities. The resulting isodose lines were visually assessed for conformality. Dose-volume histograms were extracted from ViewRay and plotted together with those from the original planning system. Finally, ViewRay plans were also examined by their ability to meet QUANTEC dose restraints.


RESULTS
A pancreas plan created using the images of a patient who underwent IMRT with Tomo Therapy resulted in satisfactory conformality assessed by the coverage of the 98% isodose line. The DVH demonstrated shallower dose fall-off for the PTV compared with TomoTherapy, as expected for a Cobalt-60 based treatment. Normal tissue DVH lines for View Ray surpassed QUANTEC dose constraints or performed as well as Tomo Therapy for all structures except kidney. Comparison with non-IMRT Pinnacle cases also exhibited good conformality and satisfied QUANTEC restraints.


CONCLUSIONS
View Ray created a feasible plan generally matching most normal tissue restrictions. Of course, the IMRT gold-standard Tomo Therapy outperformed View Ray regarding the steepness of DVH dose fall-off. In the future, more cases will be studied to perform a more complete analysis. Also, we will investigate the Co-60 dose profiles to assess penumbra directly. The View Ray TPS has the potential for comparable plans in the hands of experienced planners.