Introducing an Experimental Approach to Predict Spot Scanning Time Parameters for a Superconducting Cyclotron Proton Therapy Machine

Document Type

Conference Proceeding

Publication Date


Publication Title

International Journal of Radiation Oncology, Biology, Physics


Purpose/Objective(s): Proton pencil beam scanning (PBS) delivery sequence varies a lot among institutions due to the differences in vendors, machine types, and beamline configurations, which impacts PBS interplay effects and treatment delivery time estimation. This study aims to develop an independent experimental approach to predict the spot scanning time parameters for a clinical superconducting cyclotron proton therapy machine. Materials/Methods: This independent experimental approach employed an open-air parallel-plate detector with a temporal resolution of 0.05ms. A series of spot, energy, and dose rate patterns were designed and delivered, including (1) Spot switching time (SSWT) under different spot spacing for IEC-X, IEC-Y directions and diagonal direction (traveling in both X and Y direction) for three energy layers (110, 170 and 230 MeV); The Wilcoxon test is used to validate the prediction of SSWT along the diagonal direction. (2) Energy layer switching time (ELST) with different descending energy gaps for a fixed initial energy and different initial energies for a fixed descending energy gap. (3) Dose rate (MU/min) are measured for different minimum-MU-per-energy-layer (MMPEL), which are compared with the previous publication. Results: A SSWT jump at 10mm (can be customized) spot spacing is observed because of triggering the machine’s “raster mode” threshold. Discontinuous two variable piecewise linear functions were used to fit the SSWT in X/Y for spot spacing and energy. SSWT in X/Y is increasing as spot spacing and energy increase. SSWT in the diagonal direction is determined by the time either in the x-direction or y-direction, whichever takes longer (see Table 1 for one example of validations). ELST is linear depending on descending energy gap. The dose rate dependence on MMPEL is confirmed with previous publications of a similar type of machine. Conclusion: The study provided the first independent quantitative experimental modeling of the beam delivery time parameters without any information from vendors. Such machine-specific delivery sequence models could pave the foundation of precise interplay effect evaluation for clinical decision-making.




2 Suppl.

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American Society for Radiation Oncology 65th Annual Meeting ASTRO 2023, October 1-4, 2023, San Diego, CA