AUTHOR=Maradia Vivek , Meer David , Weber Damien Charles , Lomax Antony John , Schippers Jacobus Maarten , Psoroulas Serena TITLE=Application of a scattering foil to increase beam transmission for cyclotron based proton therapy facilities JOURNAL=Frontiers in Physics VOLUME=10 YEAR=2022 URL=https://www.frontiersin.org/journals/physics/articles/10.3389/fphy.2022.919787 DOI=10.3389/fphy.2022.919787 ISSN=2296-424X ABSTRACT=

In proton therapy, high dose rates can reduce treatment delivery times, allowing for efficient mitigation of tumor motion, as well as increased treatment efficiency and patient throughput. In cyclotron-based facilities, however, high dose rates are difficult to achieve at low-energies. In current facilities, the emittance after the degrader is matched in both transversal planes using circular collimators; this does not provide an optimal matching to the acceptance of the following beamline. However, transmission can be substantially improved by transporting maximum acceptable emittances in the X and Y planes, but at the cost of an elliptical beam shape at the gantry entrance, leading to gantry angle-dependent beam shapes at the isocenter. Here we demonstrate that equal emittances in both planes can be recovered at the gantry entrance using a thin scattering foil, thus ensuring gantry angle-independent beam shape at the isocenter. Using modified beam optics and thin scattering foil placed in the beamline, we demonstrate experimentally that low-energy beam transmission can be increased by a factor of three compared to the currently used beam optics, whilst preserving gantry angle-independent beam shapes, at the cost of a large beam size. We expect that this approach could also bring a similar transmission improvement in other cyclotron-based proton therapy facilities.