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Session: FLASH Radiotherapy - Radiobiology, Treatment Planning and Dosimetry - II [Return to Session]

BEST IN PHYSICS (THERAPY): Dose and Dose Rate Optimization for FLASH Proton Therapy with Automated Bragg Peak and Shoot-Through Beam Selection

P Ramesh1*, W Gu2, D Ruan1, K Sheng1, (1) UCLA School of Medicine, Los Angeles, CA, (2) University of Pennsylvania, Philadelphia, PA


TH-A-202-2 (Thursday, 7/14/2022) 7:30 AM - 8:30 AM [Eastern Time (GMT-4)]

Room 202

Purpose: The combined use of Bragg peak and shoot-through beams at ultra-high dose rates has been shown to reduce normal-tissue toxicities while maintaining dose conformality. Both physical dose and the FLASH effect depend on the beam orientation selection, but the joint optimization problem for all three elements has neither been proposed nor solved. To maximize the proton FLASH effect, here, we incorporate dose rate objectives into our beam orientation optimization (BOO) framework.

Methods: From our previously developed group-sparsity dose objectives, we add upper and lower dose rate terms using the dose-averaged dose rate (DADR) definition and solve using the fast-iterative shrinking threshold algorithm. We compare the dosimetry for three head-and-neck cases between four techniques: 1) Bragg peak (BP) 2) Bragg peak with dose rate optimization (BP-DR), 3) shoot-through with dose rate optimization (ST-DR), and 4) combined BP and ST (BPST-DR), with the goal of sparing OARs without loss of tumor coverage and maintaining high dose rate within a 10mm region of interest (ROI) surrounding the CTV.

Results: For [BP, BP-DR, ST-DR, BPST-DR], CTV HI and Dmax were found to be on average [0.934, 0.950, 0.670, 0.894] and [100%, 99.2%, 134%, 116%] of prescription, respectively. Mean body dose was [0.82, 0.96, 2.1, 1.4] Gy. Volume of ROIs receiving greater than 40 Gy/s was [57.5%, 92.3%, 97.2%, 98.1%] on average.

Conclusion: The dose rate techniques, particularly BPST-DR, were able to significantly increase dose rate without compromising physical dose. Our algorithm efficiently selects beams that are optimal for both dose and dose rate.

Funding Support, Disclosures, and Conflict of Interest: This project is supported by NIH R01CA230278.


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