Room: Exhibit Hall
Purpose: To study and design ridge filters and modulating wheels devices for generating Spread out Bragg peaks (SOBP) for a small animal proton pencil beam facility.
Methods: Our small animal facility includes a static pencil beam with 70 MeV energy and pencil beam size in air with full width half maximum (FWHM) of 10 mm. We have considered beam modulations with SOBP ranging from 5 mm to 20 mm for this study. We use TOPAS, the particle simulation toolkit based on GEANT4 for designing and verifications. Simulation for a ridge filters include varying the parameters such as ridge peak height and ridge width to achieve the desired SOBPs. To design a range modulator wheel, we used 10 pristine proton depth-dose curves in water with the thickness of Lexan blocks ranging from 25mm to 34mm as basis functions to calculate the weight factor for each blocks thickness on the modulator wheel.
Results: Based on our simulations we constructed 3D printed ridge filters and modulator wheels. Our simulation studies including experimental verification of constructed devices shows that it is more difficult to obtain flat and smooth SOBP width with ridge filters due to the pencil beam size and energy as compared to modulator wheels. Furthermore, sub-millimeter resolution is required for the 3D printer in order to obtain the SOBP with flatness less than 5% for the ridge filter.
Conclusion: Both modulator wheels and ridge filters could be used for generating SOBPs for proton pencil beams utilized in small animal facility. Modulator wheel provides smoother SOBPs as compared to ridge filters and their use is preferred.
Not Applicable / None Entered.