Author: Julien Bancheri, Chau Giang Bui, Christopher M Lund, Morgan J Maher, Jamiel Nasser, Amy Parent, Monica Serban, Jan P. Seuntjens, Jason Z Yuan 👨🔬
Affiliation: University of Toronto, Medical Physics Unit, McGill University, Princess Margaret Cancer Centre, Princess Margaret Cancer Centre & University of Toronto 🌍
Purpose: Proton therapy (PT) has demonstrated greater precision and superior healthy tissue sparing compared to photon radiotherapy for various sites; however, PT systems are expensive, which limits global availability. The dielectric wall accelerator (DWA) is proposed as a low-cost, compact PT system. In this work, we compare the spot sizes and surface dose from our DWA model to those from conventional PT.
Methods: A linear beam optics model of the DWA was developed using TRANSOPTR. The proton bunches, of energies 20 to 230 MeV, were simulated through a DWA beamline before passing through nozzle components in TOPAS. For comparison, an IBA proton beam was simulated in TOPAS, with and without Lexan and polyethylene range shifters of 7-g/cm2 thickness. For all configurations, lateral spot sizes were measured in air; longitudinal spot sizes in water.
Results: Compared to IBA proton beams, DWA protons exhibited a 67.0% average reduction in lateral spot size over ranges from 7 to 21 cm (corresponding to 100 to 175 MeV) and a 76.8% reduction in ranges below 7 cm, averaged over both range shifters. For the longitudinal spot size, DWA protons had a 21.5% average reduction compared to IBA due to their lower beam energy spread. Since achieving a spot size of 5 mm or less has been shown to yield highly conformal plans, DWA protons have the potential to maintain clinical plan quality. Surface dose results also inform our lower energy limit to be 50 MeV (corresponding to a range of 2.2 cm and surface dose of 19.8%) to prevent high irradiation to the patient’s skin.
Conclusion: DWA technology may lead to improved spot sizes compared to conventional PT, providing opportunity for more conformal treatment plans. Future work will focus on treatment plan comparisons to further assess the impacts of reduced spot sizes.