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A Comparison of IMRT Plans for the ViewRay MR-Guided RT System with TomoTherapy and Pinnacle

D Saenz

Daniel Saenz*, John Bayouth, Bhudatt Paliwal, University of Wisconsin, Madison, WI

SU-E-T-614 Sunday 3:00PM - 6:00PM Room: Exhibit Hall

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 TomoTherapy 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 ViewRay surpassed QUANTEC dose constraints or performed as well as TomoTherapy for all structures except kidney. Comparison with non-IMRT Pinnacle cases also exhibited good conformality and satisfied QUANTEC restraints.

Conclusions: ViewRay created a feasible plan generally matching most normal tissue restrictions. Of course, the IMRT gold-standard TomoTherapy outperformed ViewRay 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 ViewRay TPS has the potential for comparable plans in the hands of experienced planners.

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