Geometry optimisation of graphite energy degrader for proton therapy |
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| Institution: | 1. School of Physics and Astronomy, The University of Manchester, Manchester M13 9PL, United Kingdom;2. The Cockcroft Institute, Daresbury Science and Innovation Campus, Warrington WA4 4AD, United Kingdom;3. Paul Scherrer Institute, 5232 Villigen, Switzerland;1. Radiation Oncology Department, 3rd Affiliated Hospital of Qiqihar Medical University, Qiqihar, China;2. Radiation Oncology Department, Fox Chase Cancer Center, Philadelphia, PA, United States;1. Istituto Nazionale di Fisica Nucleare, Sezione di Catania, Italy;2. MIFT Department, University of Messina, Italy;3. Section of Radiological Sciences, Department of Biomedical and Dental Sciences and Morphofunctional Imaging, University of Messina, Italy;1. Biophysics, GSI Helmholtzzentrum für Schwerionenforschung GmbH, Darmstadt, Germany;2. Department of Physics and Astronomy, Louisiana State University, Baton Rouge, LA, USA;3. Research and Development Department, Centro Nazionale di Adroterapia Oncologica, Pavia, Italy;4. Department of Radiation Physics, Mary Bird Perkins Cancer Center, Baton Rouge, LA, USA;5. Institute of Condensed Matter Physics, Technical University of Darmstadt, Germany;1. Center for Proton Therapy, Paul Scherrer Institute, Villigen PSI, Switzerland;2. Department of Oncology, Rigshospitalet Copenhagen University Hospital, Copenhagen, Denmark;3. Niels Bohr Institute, University of Copenhagen, Copenhagen, Denmark;4. Department of Radiation Oncology, University Hospital of Zürich, Zürich, Switzerland;6. Department of Physics, ETH Zürich, Zürich, Switzerland |
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| Abstract: | Introduction: Cyclotron-based proton therapy facilities use an energy degrader of variable thickness to deliver beams of the different energies required by a patient treatment plan; scattering and straggling in the degrader give rise to an inherent emittance increase and subsequent particle loss in the downstream energy-selection system (ESS). Here we study alternative graphite degrader geometries and examine with Monte-Carlo simulations the induced emittance growth and consequent particle transmission.Methods: We examined the conventional multiple-wedge degrader used in the Paul Scherrer Institute PROSCAN proton therapy system, the equivalent parallel-sided degrader, and a single block degrader of equivalent thickness. G4Beamline Monte-Carlo tracking of protons was benchmarked against measurements of the existing degrader for proton energies from 75 to 230 MeV, and used to validate simulations of the alternative geometries.Results: Using a careful calculation of the beam emittance growth, we determined that a single-block degrader placed close to the collimators of the ESS is expected to deliver significantly larger transmission, up to 17% larger at 150 MeV. At the lowest deliverable of 75 MeV there is still a clear improvement in beam transmission.Conclusions: Whilst dose rates are not presently limited on the PROSCAN system at higher energies, a single-block degrader offers the ability to access either lower energies for treatment or a larger dose rate at 75 MeV in case transmission optimisation is desired. Single-block degraders should be considered for the delivery of low-energy protons from a cyclotron-based particle therapy system. |
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| Keywords: | Energy degrader Monte-Carlo simulations Proton therapy Graphite |
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