Purpose: To investigate treatment plans generated using the Raystation RS6 based on the Mevion HYPERSCAN beam characteristics and compare the results with traditional beam-line based proton systems.
 
Method: Clinical plans generated for patient treatments at GUH from March, 2018 to December, 2018 were analyzed for four  anatomical sites of brain, lung, pancreas and prostate. Plan parameters evaluated include clinical goals specified by the clinicians, volumetric and planar dose distributions. Treatment plans were recomputed using the same beam configurations for a generic beamline-based proton model and compared with the HYPERSCAN plans. With PTV coverage meeting the clinical goals, DVHs were evaluated for relevant OARs.
Results and Discussions: All treatment plans met the clinical goals set forth by the clinicians--some of them with minor deviations. Unique to the HYPERSCAN are the constant Bragg peak width and progressively larger spot sizes at lower energies, and an Adaptive Aperture for spot size trimming. Potential impacts of such beam characteristics are mostly reflected in the distal and proximal region, as well as lateral regions. On average, while the AA enables penumbra trimming to meet  clinical goals on OARs, higher doses to varying degrees were observed in lateral planes for the HYPERSCAN plans, although such doses were judged to be of no clinical significance by the clinicians. 

The larger spots sizes of the HYPERSCAN were remedied by the use of the AA, and the impact of a constant Bragg peak width was mostly reflected as slightly higher doses proximal to the PTVs for sallower targets. However, higher doses in this region of the HYPERSCAN are of no clinical significance.      

It is anticipated that HYPERSCAN plans will be more robust when organ motion, setup uncertainty and influence of heterogeneity are taken into considerations. Further evaluations are underway.

Evaluation of Treatment Plans Based on the Mevion Hyperscan Beam Characteristics