Feasibility of 3D Printed Ridge Filter to Enable SBRT FLASH Therapy Using Scanning Proton Beam
R Liu1*, S Charyyev2, J Zhou3, X Yang4, T Liu5, M McDonald6, K Higgins7, J Bradley8, L Lin9, (1) Emory University, Atlanta, GA (2) Emory Univeristy, Atlanta, GA, (3) Emory University, Atlanta, GA, (4) Emory University, Atlanta, GA, (5) Emory Univ, Atlanta, GA, (6) Emory University, Atlanta, GA, (7) Emory Univ, Atlanta, GA, (8) Emory University School Of Medicine, ,,(9) Emory Proton Therapy Center, Atlanta, GA
Presentations
TU-F-TRACK 5-2 (Tuesday, 7/27/2021) 4:30 PM - 5:30 PM [Eastern Time (GMT-4)]
Purpose: Due to long proton energy switching time, most FLASH therapy is limited to single energy and to spare normal tissue without conformity of treatment target along the depth direction. We investigate if a 3D ridge filter can enable dose conformity of stereotactic radiation therapy (SBRT) target in FLASH treatment using scanning proton beams.
Methods: Varian ProBEAM’s FLASH energy of 250 MeV was degraded to 120 MeV to treat simulated SBRT spherical targets of 30 mm and 50 mm diameters at depths of ~80 mm of a water phantom. We develop a method to optimize the height and location of the PMMA pins of the ridge filter so that the spread-out Bragg peaks at each location can correspond to that of the sphere targets. The ridge filter pins must meet the 0.1-mm lateral and height resolutions of a 3D printer. Geant4 was used to simulate radiation transport. The spot weights were also optimized to achieve lateral target conformity.
Results: The simulation results showed that it is feasible to use 3D printed ridge filters to achieve location-dependent spread-out Bragg peaks for SBRT spherical targets for one fixed energy. Delivering 10 Gy dose in such spot maps is estimated to be below 250 ms, achieving a Flash dose rate of 40 Gy/s. The validation of timing and simulated dosimetric distributions will be performed since Flash mode has been recently delivered at Emory.
Conclusion: According to Geant4 simulation, it is feasible to use a 3D ridge filter to enable proton SBRT FLASH therapy up to 50 mm diameter sphere target.
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