Author: Mark A. Newpower, Jill Taylor 👨🔬
Affiliation: University of Oklahoma Health Sciences Center 🌍
Purpose: RayStation 2024A allows planners to optimize intensity modulated proton therapy (IMPT) plans using discrete arcs which can then be converted to traditional pencil beam scanning (PBS) beams for delivery with current technology. As we evaluate this new planning approach, our first step is to develop plans that are dosimetrically equivalent, or better, than PBS plans. In this work, we present a study of two brain plans optimized with PBS arcs and converted to PBS plans. Our working hypothesis is that PBS Arc converted plans will be dosimetrically equivalent, in terms of organ at risk (OAR) sparing and target coverage, to the original clinical plans.
Methods: Using RayStation 2024A, we re-planned two brain cancer patients using PBS arcs. PBS arc plans were created and converted into PBS plans: Plan 1 for a glioma patient and Plan 2 for a chordoma patient. In Plan 1, the PBS Arc plan was converted to a PBS plan with the same number of beam angles (3), while Plan 2 was converted into an 8-beam plan. The resulting plans were compared to the original clinical plans to determine if the arc plans offered superior OAR sparing while maintaining the same level of target coverage.
Results: The PBS arc plans converted to PBS resulted in similar target and OAR coverage as compared to the clinical plan. Plan 1’s PBS Arc plan 1 was much more conformal than the clinical plan, while Plan 2’s PBS Arc plan better spared the brainstem compared to the clinical plan. For Plan 2, we developed a discrete arc plan consisting of more beams than is typically used.
Conclusion: Optimizing plans with arcs and converting to PBS resulted in similar plan quality in terms of OAR sparing and target coverage, compared to our current planning approach with PBS beams.