Experimental assessment of proton dose calculation accuracy in inhomogeneous media |
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| Affiliation: | 1. Université catholique de Louvain, Molecular Imaging Radiotherapy & Oncology, Brussels, Belgium;2. Université catholique de Louvain, ICTEAM Institute, Louvain-la-Neuve, Belgium;3. Yonsei University, Department of Radiation Convergence Engineering, Wonju, South Korea;4. Massachusetts General Hospital and Harvard Medical School, Department of Radiation Oncology, Boston, MA 02114, USA;5. Ion Beam Applications s.a, Louvain-la-Neuve, Belgium;6. Raysearch Laboratories AB, Stockholm, Sweden;7. Cliniques Universitaires Saint-Luc, Brussels, Belgium;8. KU Leuven, Department of Oncology, Laboratory of Experimental Radiotherapy, Leuven, Belgium;1. Cavendish Laboratory, University of Cambridge, UK;2. Department of Oncology, University of Cambridge, UK;3. Cambridge University Hospitals NHS Foundation Trust, UK;1. Medical Physics Department, AUSL 4 Teramo – Hospital G. Mazzini, Piazza Italia 1, 64100 Teramo (TE), Italy;2. Post-graduate School in Medical Physics, University of L’Aquila, Piazzale Salvatore Tommasi 1, 67100 L’Aquila (AQ), Italy;1. Humanitas Research Hospital and Cancer Center, Radiotherapy and Radiosurgery Dept, via Manzoni 56, 20089 Milan-Rozzano, Italy;2. Humanitas University, Biomedical Science Faculty, via Manzoni 118, 20089 Milan-Rozzano, Italy;1. New York Proton Center, New York, NY 10035, USA;2. City of Hope, Orange County, Irvine, CA 92618, USA;1. Department of Radiotherapy Physics, Northern Centre for Cancer Care, Freeman Hospital, Freeman Road, Newcastle upon Tyne NE7 7DN, UK;2. RaySearch Laboratories AB, Stockholm, Sweden |
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| Abstract: | PurposeProton therapy with Pencil Beam Scanning (PBS) has the potential to improve radiotherapy treatments. Unfortunately, its promises are jeopardized by the sensitivity of the dose distributions to uncertainties, including dose calculation accuracy in inhomogeneous media. Monte Carlo dose engines (MC) are expected to handle heterogeneities better than analytical algorithms like the pencil-beam convolution algorithm (PBA). In this study, an experimental phantom has been devised to maximize the effect of heterogeneities and to quantify the capability of several dose engines (MC and PBA) to handle these.MethodsAn inhomogeneous phantom made of water surrounding a long insert of bone tissue substitute (1 × 10 × 10 cm3) was irradiated with a mono-energetic PBS field (10 × 10 cm2). A 2D ion chamber array (MatriXX, IBA Dosimetry GmbH) lied right behind the bone. The beam energy was such that the expected range of the protons exceeded the detector position in water and did not attain it in bone. The measurement was compared to the following engines: Geant4.9.5, PENH, MCsquare, as well as the MC and PBA algorithms of RayStation (RaySearch Laboratories AB).ResultsFor a γ-index criteria of 2%/2 mm, the passing rates are 93.8% for Geant4.9.5, 97.4% for PENH, 93.4% for MCsquare, 95.9% for RayStation MC, and 44.7% for PBA. The differences in γ-index passing rates between MC and RayStation PBA calculations can exceed 50%.ConclusionThe performance of dose calculation algorithms in highly inhomogeneous media was evaluated in a dedicated experiment. MC dose engines performed overall satisfactorily while large deviations were observed with PBA as expected. |
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| Keywords: | Proton therapy Pencil beam scanning Inhomogeneous phantom Monte carlo Quality assurance |
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