Feasibility of Customized Hole Filters for FLASH Irradiation
X Zhao*, F Reynoso, A Darafsheh, T Zhao, Washington University School of Medicine, St. Louis, MO
Presentations
PO-GePV-T-158 (Sunday, 7/10/2022) [Eastern Time (GMT-4)]
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Purpose: Dose distribution in shoot-through FLASH proton therapy has sub-optimal conformity to the target volume due to the limited energy layers required to maintain the ultra-high dose rate (> 40 Gy/s). In order to achieve an optimal dose conformity customized to a target volume, we aimed to design range modulating devices composed of an array of cavities in a range shifting block capable of producing various spread-out Bragg peaks (SOBPs) tailored to a given target volume.
Methods: A monoenergetic 230 MeV proton beam with 5.4 mm sigma for the spot size, and 1.5 mrad beam divergence at isocenter was simulated in this study. Our designed range modulating device, a “hole filter”, is composed of an array of holes in a slab made with material of low atomic number between the exiting window of a proton beamline and a treatment target. The hole diameters and slab thickness are optimized for desired SOBP, flatness and range. The fine structure in the hole filter can be 3D printed. We performed Geant4 Monte Carlo simulation to systematically evaluate the performance of our designed devices and find the optimal designs corresponding to a desired modulation depth and target volume.
Results: A close correlation between the SOBP width and hole diameter is determined through polynomial regression fitting. SOBP width from 1cm to 4cm were achieved with flatness between 0.6 and 3.9% with our design. A hemisphere-like dose distribution is achieved by optimizing a hole filter with 5 different hole size and thickness.
Conclusion: Optimal design of hole filters can produce SOBP beams with optimal conformity of the dose to a given target volume. Our work can be used as a guideline for fabricating such a device.
Keywords
Taxonomy
TH- External Beam- Particle/high LET therapy: Proton therapy – computational dosimetry-Monte Carlo
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