Dose Enhancement Effects of High-Z Foils in Proton Radiation Therapy
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PO-GePV-T-129 (Sunday, 7/10/2022) [Eastern Time (GMT-4)]
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Purpose: To study the dose enhancements, Bragg Peak shifts, and narrowing of the Bragg Peak widths of high-z foils in proton beam Monte Carlo simulation. High-z materials have been shown to increase the number of secondary electrons and enhance localized dose to the target volume and shift the Bragg Peak upstream. This study compares the dose of a water phantom with gold, silver, and platinum foils to that of a water phantom with no foils.
Methods: Two water phantoms of 30cm x 30cm x 40cm were created using TOPAS 3.6.1 which wraps and extends Geant4 simulation toolkit to make advanced Monte Carlo simulation for radiotherapy. The control phantom consisted of pure water. The custom phantom consisted of foils of gold, platinum, or silver in water. The location of the foils was in the proximal to distal 80% Bragg Peak widths. The energies simulated were 60, 100, 160 and 226 MeV proton beam with spot size of 2.7mm diameter. Depth dose deposited each from 5 million protons was calculated in 0.1 mm resolution. The dose enhancement factors, the shifts in the Bragg Peak, as well as the narrowing of the Bragg Peak widths were quantized. Modular physics list included g4em-standard_opt3, g4h-phy_QGSP_BIC_HP, g4decay, g4ion-binarycascade, g4h-elastic_HP and g4stopping.
Results: The introduction of foils in the simulations shifts Bragg peak towards upstream direction, increases delivered dose, and narrows the Bragg Peak width compared to that of control phantom. Largest shift occurs with platinum foil at the highest proton energy, largest dose enhancement occurs also for platinum but with lowest proton energy. Narrowing of Bragg Peak widths were not fixed.
Conclusion: In this study, we simulated high-z foils in proton beams of different energies. Our results show a dose enhancement effect, proximal Bragg Peak shift, and narrowing of the 80-80% Bragg Peak width.
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