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Session: Therapy: Particle Therapy Treatment Planning [Return to Session]

Adaptive Spot Placement Method for Pencil Beam Scanning Proton Therapy

B Lin1,2, Y Lin1, M McDonald1, J Bradley1, S Fu2, H Gao2*, (1) Winship Cancer Institute of Emory University, Atlanta, GA, (2) Shandong University, Jinan, Shandong, China

Presentations

TU-IePD-TRACK 5-5 (Tuesday, 7/27/2021) 12:30 PM - 1:00 PM [Eastern Time (GMT-4)]

Purpose: Although pencil beam scanning (PBS) proton radiotherapy (RT) can provide flexible proton spot placement for intensity modulated proton therapy (IMPT), currently the spot placement is mostly based on a fixed Cartesian grid (FG), without fully accounting for the geometry of tumor targets. This work will develop an adaptive Cartesian grid (AG) spot placement method, which will be highly adaptive to the geometry of tumor targets.

Methods: Given the simplicity and universality of the Cartesian grid to place spots for tumor targets that can be arbitrarily shaped, AG is based on the Cartesian grid. However, compared with FG, AG places (1) a relatively fine grid of spots at the boundary of tumor targets to account for the geometry of tumor targets and treatment uncertainties (setup and range uncertainty) for improving dose conformality, and (2) a relatively coarse grid of spots in the interior of tumor targets to reduce the number of spots and increase the spot weights for improving delivery efficiency.

Results: AG was validated using representative clinical cases in comparison with FG, with clinically used DVH planning objectives, beam angles, and uncertainty level. The same plan objectives, the same optimization algorithm, and the same plan normalization were used for the fair comparison of AG and FG. The preliminary results demonstrate that AG provided better plan quality than FG in both target coverage and OAR sparing, with up to 50-60% reduction in number of spots.

Conclusion: We have developed an AG spot placement method with adaptive Cartesian grid that is fully compatible with existing treatment planning convention and systems. Compared with the conventional FG on a fixed Cartesian grid, AG can improve both lateral dose falloff (for better plan quality) and spot utility (for better delivery efficiency).

Funding Support, Disclosures, and Conflict of Interest: This research is supported in part by Varian Medical Systems and NIH grant R01CA250921.

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