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Ates O, Uh J, Pirlepesov F, Hua CH, Triplett B, Qudeimat A, Sharma A, Merchant TE, Lucas JT. Interplay Effect of Splenic Motion for Total Lymphoid Irradiation in Pediatric Proton Therapy. Cancers (Basel) 2023; 15:5161. [PMID: 37958335 PMCID: PMC10650483 DOI: 10.3390/cancers15215161] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/20/2023] [Revised: 10/24/2023] [Accepted: 10/24/2023] [Indexed: 11/15/2023] Open
Abstract
(1) Background: The most significant cause of an unacceptable deviation from the planned dose during respiratory motion is the interplay effect. We examined the correlation between the magnitude of splenic motion and its impact on plan quality for total lymphoid irradiation (TLI); (2) Methods: Static and 4D CT images from ten patients were used for interplay effect simulations. Patients' original plans were optimized based on the average CT extracted from the 4D CT and planned with two posterior beams using scenario-based optimization (±3 mm of setup and ±3% of range uncertainty) and gradient matching at the level of mid-spleen. Dynamically accumulated 4D doses (interplay effect dose) were calculated based on the time-dependent delivery sequence of radiation fluence across all phases of the 4D CT. Dose volume parameters for each simulated treatment delivery were evaluated for plan quality; (3) Results: Peak-to-peak splenic motion (≤12 mm) was measured from the 4D CT of ten patients. Interplay effect simulations revealed that the ITV coverage of the spleen remained within the protocol tolerance for splenic motion, ≤8 mm. The D100% coverage for ITV spleen decreased from 95.0% (nominal plan) to 89.3% with 10 mm and 87.2% with 12 mm of splenic motion; (4) Conclusions: 4D plan evaluation and robust optimization may overcome problems associated with respiratory motion in proton TLI treatments. Patient-specific respiratory motion evaluations are essential to confirming adequate dosimetric coverage when proton therapy is utilized.
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Affiliation(s)
- Ozgur Ates
- St. Jude Children’s Research Hospital, Memphis, TN 38105, USA; (J.U.); (F.P.); (C.-h.H.); (B.T.); (A.Q.); (A.S.); (T.E.M.); (J.T.L.J.)
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2
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Knäusl B, Lebbink F, Fossati P, Engwall E, Georg D, Stock M. Patient Breathing Motion and Delivery Specifics Influencing the Robustness of a Proton Pancreas Irradiation. Cancers (Basel) 2023; 15:cancers15092550. [PMID: 37174016 PMCID: PMC10177445 DOI: 10.3390/cancers15092550] [Citation(s) in RCA: 7] [Impact Index Per Article: 7.0] [Reference Citation Analysis] [Abstract] [Key Words] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/27/2023] [Revised: 04/24/2023] [Accepted: 04/28/2023] [Indexed: 05/15/2023] Open
Abstract
Motion compensation strategies in particle therapy depend on the anatomy, motion amplitude and underlying beam delivery technology. This retrospective study on pancreas patients with small moving tumours analysed existing treatment concepts and serves as a basis for future treatment strategies for patients with larger motion amplitudes as well as the transition towards carbon ion treatments. The dose distributions of 17 hypofractionated proton treatment plans were analysed using 4D dose tracking (4DDT). The recalculation of clinical treatment plans employing robust optimisation for mitigating different organ fillings was performed on phased-based 4D computed tomography (4DCT) data considering the accelerator (pulsed scanned pencil beams delivered by a synchrotron) and the breathing-time structure. The analysis confirmed the robustness of the included treatment plans concerning the interplay of beam and organ motion. The median deterioration of D50% (ΔD50%) for the clinical target volume (CTV) and the planning target volume (PTV) was below 2%, while the only outlier was observed for ΔD98% with -35.1%. The average gamma pass rate over all treatment plans (2%/ 2 mm) was 88.8% ± 8.3, while treatment plans for motion amplitudes larger than 1 mm performed worse. For organs at risk (OARs), the median ΔD2% was below 3%, but for single patients, essential changes, e.g., up to 160% for the stomach were observed. The hypofractionated proton treatment for pancreas patients based on robust treatment plan optimisation and 2 to 4 horizontal and vertical beams showed to be robust against intra-fractional movements up to 3.7 mm. It could be demonstrated that the patient's orientation did not influence the motion sensitivity. The identified outliers showed the need for continuous 4DDT calculations in clinical practice to identify patient cases with more significant deviations.
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Affiliation(s)
- Barbara Knäusl
- Department of Radiation Oncology, Medical University of Vienna, 1090 Vienna, Austria
- MedAustron Ion Therapy Centre, Medical Physics, 2700 Wiener Neustadt, Austria
| | - Franciska Lebbink
- Department of Radiation Oncology, Medical University of Vienna, 1090 Vienna, Austria
- MedAustron Ion Therapy Centre, Medical Physics, 2700 Wiener Neustadt, Austria
| | - Piero Fossati
- MedAustron Ion Therapy Centre, Medical Physics, 2700 Wiener Neustadt, Austria
- Division Medical Physics, Karl Landsteiner University of Health Sciences, 2700 Wiener Neustadt, Austria
| | | | - Dietmar Georg
- Department of Radiation Oncology, Medical University of Vienna, 1090 Vienna, Austria
| | - Markus Stock
- MedAustron Ion Therapy Centre, Medical Physics, 2700 Wiener Neustadt, Austria
- Division Medical Physics, Karl Landsteiner University of Health Sciences, 2700 Wiener Neustadt, Austria
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3
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Late Radiation-Induced Carotid Artery Stenosis and Stroke in Pediatric Patient Treated With Proton Radiation Therapy for Skull-Base Chordoma. Pract Radiat Oncol 2023:S1879-8500(23)00001-2. [PMID: 36641091 DOI: 10.1016/j.prro.2022.12.007] [Citation(s) in RCA: 1] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/03/2022] [Revised: 12/20/2022] [Accepted: 12/31/2022] [Indexed: 01/13/2023]
Abstract
Radiation vasculopathy is a well-recognized late complication of radiation therapy. We present a case of a stroke 29 years after high-dose proton radiation therapy for skull-base chordoma due to occlusion of bilateral internal carotid arteries.
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Taylor S, Lim P, Ahmad R, Alhadi A, Harris W, Rompokos V, D'Souza D, Gaze M, Gains J, Veiga C. Risk of radiation-induced second malignant neoplasms from photon and proton radiotherapy in paediatric abdominal neuroblastoma. Phys Imaging Radiat Oncol 2021; 19:45-52. [PMID: 34307918 PMCID: PMC8295851 DOI: 10.1016/j.phro.2021.06.003] [Citation(s) in RCA: 5] [Impact Index Per Article: 1.7] [Reference Citation Analysis] [Abstract] [Key Words] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/25/2021] [Revised: 05/28/2021] [Accepted: 06/18/2021] [Indexed: 12/02/2022] Open
Abstract
BACKGROUND AND PURPOSE State-of-the-art radiotherapy modalities have the potential of reducing late effects of treatment in childhood cancer survivors. Our aim was to investigate the carcinogenic risk associated with 3D conformal (photon) radiation (3D-CRT), intensity modulated arc therapy (IMAT) and pencil beam scanning proton therapy (PBS-PT) in the treatment of paediatric abdominal neuroblastoma. MATERIALS AND METHODS The risk of radiation-induced second malignant neoplasm (SMN) was estimated using the concept of organ equivalent dose (OED) for eleven organs (lungs, rectum, colon, stomach, small intestine, liver, bladder, skin, central nervous system (CNS), bone, and soft tissues). The risk ratio (RR) between radiotherapy modalities and lifetime absolute risks (LAR) were reported for twenty abdominal neuroblastoma patients (median, 4y; range, 1-9y) historically treated with 3D-CRT that were also retrospectively replanned for IMAT and PBS-PT. RESULTS The risk of SMN due to primary radiation was reduced in PBS-PT against 3D-CRT and IMAT for most patients and organs. The RR across all organs ranged from 0.38 ± 0.22 (bladder) to 0.98 ± 0.04 (CNS) between PBS-PT and IMAT, and 0.12 ± 0.06 (rectum and bladder) to 1.06 ± 0.43 (bone) between PBS-PT and 3D-CRT. The LAR for most organs was within 0.01-1% (except the colon) with a cumulative risk of 21 ± 13%, 35 ± 14% and 35 ± 16% for PBS-PT, IMAT and 3D-CRT, respectively. CONCLUSIONS PBS-PT was associated with the lowest risk of radiation-induced SMN compared to IMAT and 3D-CRT in abdominal neuroblastoma treatment. Other clinical endpoints and plan robustness should also be considered for optimal plan selection.
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Affiliation(s)
- Sophie Taylor
- Centre for Medical Image Computing, Department of Medical Physics and Biomedical Engineering, University College London, London, UK
| | - Pei Lim
- Department of Oncology, University College London Hospitals NHS Foundation Trust, London, UK
| | - Reem Ahmad
- Centre for Medical Image Computing, Department of Medical Physics and Biomedical Engineering, University College London, London, UK
| | - Ammar Alhadi
- Centre for Medical Image Computing, Department of Medical Physics and Biomedical Engineering, University College London, London, UK
| | - William Harris
- Centre for Medical Image Computing, Department of Medical Physics and Biomedical Engineering, University College London, London, UK
| | - Vasilis Rompokos
- Radiotherapy Physics Services, University College London Hospitals NHS Foundation Trust, London, UK
| | - Derek D'Souza
- Radiotherapy Physics Services, University College London Hospitals NHS Foundation Trust, London, UK
| | - Mark Gaze
- Department of Oncology, University College London Hospitals NHS Foundation Trust, London, UK
| | - Jennifer Gains
- Department of Oncology, University College London Hospitals NHS Foundation Trust, London, UK
| | - Catarina Veiga
- Centre for Medical Image Computing, Department of Medical Physics and Biomedical Engineering, University College London, London, UK
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Lim PS, Rompokos V, Bizzocchi N, Gillies C, Gosling A, Royle G, Chang YC, Gaze MN, Gains JE. Pencil Beam Scanning Proton Therapy Case Selection for Paediatric Abdominal Neuroblastoma: Effects of Tumour Location and Bowel Gas. Clin Oncol (R Coll Radiol) 2021; 33:e132-e142. [PMID: 32962907 DOI: 10.1016/j.clon.2020.08.012] [Citation(s) in RCA: 10] [Impact Index Per Article: 3.3] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/27/2020] [Accepted: 08/28/2020] [Indexed: 12/12/2022]
Abstract
AIMS Pencil beam scanning (PBS) proton therapy is an increasingly used radiation modality for childhood malignancies due to its ability to minimise dose to surrounding organs. However, the dosimetry is extremely sensitive to anatomical and density changes. The aims of this study were to investigate if there is a dosimetric benefit or detriment with PBS for paediatric abdominal neuroblastoma, assess gastrointestinal air variability and its dosimetric consequences, plus identify if there are factors that could assist case selection for PBS referral. MATERIALS AND METHODS Twenty neuroblastoma cases were double-planned with PBS and intensity-modulated arc therapy (IMAT). Cases were divided into unilateral, midline unilateral and midline bilateral locations in relation to the kidneys. Plans were recalculated after the gastrointestinal volume was simulated as air (Hounsfield Units -700) and water (Hounsfield Units 0), then compared with nominal plans (recalculated - nominal, ΔD). Forty-three weekly cone beam computed tomography scans were analysed to quantify gastrointestinal air variability during treatment. RESULTS PBS reduced the mean dose to normal tissues at all tumour locations, particularly unilateral tumours. However, 15% had better dosimetry with IMAT, all of which were midline tumours. Increased gastrointestinal air caused significant compromises to PBS versus IMAT plans for midline tumours [median/maximum ΔD95% clinical target volume (CTV) -2.4%/-15.7% PBS versus 1.4%/0% IMAT, P = 0.003], whereas minimal impact was observed for unilateral tumours (ΔD95% CTV -0.5%/-1.9% PBS versus 0.5%/-0.5% IMAT, P = 0.008). D95% CTV was significantly decreased in PBS plans if planning target volume (PTV) ≥400 cm3 (median -4.1%, P = 0.001) or PTV extension ≥60% anterior to vertebral body (-2.1%, P = 0.002). A larger variation in gastrointestinal air was observed in patients treated under general anaesthesia (median 38.4%) versus awake (11.5%); P = 0.004. CONCLUSION In this planning study, tumours at the unilateral location consistently showed improved dose reductions to normal tissue with minimal dose degradation from increased gastrointestinal air with PBS plans. Tumour location, PTV volume and anterior extension of PTV are useful characteristics in facilitating patient selection for PBS.
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Affiliation(s)
- P S Lim
- Department of Oncology, University College London Hospitals NHS Foundation Trust, London, UK; Department of Medical Physics and Biomedical Engineering, University College London, London, UK
| | - V Rompokos
- Department of Radiotherapy Physics, University College London Hospitals NHS Foundation Trust, London, UK
| | - N Bizzocchi
- Centre for Proton Therapy, Paul Scherrer Institute, Villigen, Switzerland
| | - C Gillies
- Department of Radiotherapy Physics, University College London Hospitals NHS Foundation Trust, London, UK
| | - A Gosling
- Department of Radiotherapy Physics, University College London Hospitals NHS Foundation Trust, London, UK
| | - G Royle
- Department of Oncology, University College London Hospitals NHS Foundation Trust, London, UK; Department of Medical Physics and Biomedical Engineering, University College London, London, UK
| | - Y-C Chang
- Department of Oncology, University College London Hospitals NHS Foundation Trust, London, UK
| | - M N Gaze
- Department of Oncology, University College London Hospitals NHS Foundation Trust, London, UK
| | - J E Gains
- Department of Oncology, University College London Hospitals NHS Foundation Trust, London, UK.
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Jazmati D, Butzer S, Hero B, Ahmad Khalil D, Merta J, Bäumer C, Plum G, Fuchs J, Koerber F, Steinmeier T, Peters S, Doyen J, Thole T, Schmidt M, Blase C, Tippelt S, Eggert A, Schwarz R, Simon T, Timmermann B. Proton Beam Therapy for Children With Neuroblastoma: Experiences From the Prospective KiProReg Registry. Front Oncol 2021; 10:617506. [PMID: 33552991 PMCID: PMC7855697 DOI: 10.3389/fonc.2020.617506] [Citation(s) in RCA: 6] [Impact Index Per Article: 2.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/14/2020] [Accepted: 11/30/2020] [Indexed: 12/11/2022] Open
Abstract
Objective Radiotherapy (RT) is an integral part of the interdisciplinary treatment of patients with high-risk neuroblastoma (NB). With the continuous improvements of outcome, the interest in local treatment strategies that reduce treatment-related side effects while achieving optimal oncological results is growing. Proton beam therapy (PBT) represents a promising alternative to conventional photon irradiation with regard to the reduction of treatment burden. Method Retrospective analysis of children with high or intermediate risk NB receiving PBT of the primary tumor site during first-line therapy between 2015 and 2020 was performed. Data from the prospective in-house registry Standard Protonentherapie WPE - Kinder- (KiProReg) with respect to tumor control and treatment toxicity were analyzed. Adverse events were classified according to CTCAE Version 4 (V4.0) before, during, and after PBT. Results In total, 44 patients (24 male, 20 female) with high (n = 39) or intermediate risk NB (n = 5) were included in the analysis. Median age was 3.4 years (range, 1.4-9.9 years). PBT doses ranged from 21.0 to 39.6 Gray (Gy) (median 36.0 Gy). Five patients received PBT to the MIBG-avid residual at the primary tumor site at time of PBT according to the NB-2004 protocol. In 39 patients radiation was given to the pre-operative tumor bed with or without an additional boost in case of residual tumor. After a median follow-up (FU) of 27.6 months, eight patients developed progression, either local recurrence (n = 1) or distant metastases (n = 7). Four patients died due to tumor progression. At three years, the estimated local control, distant metastatic free survival, progression free survival, and overall survival was 97.7, 84.1, 81.8, and 90.9%, respectively. During radiation, seven patients experienced higher-grade (CTCAE ≥ °3) hematologic toxicity. No other higher grade acute toxicity occurred. After PBT, one patient developed transient myelitis while receiving immunotherapy. No higher grade long-term toxicity was observed up to date. Conclusion PBT was a well tolerated and effective local treatment in children with high and intermediate risk NB. The role of RT in an intensive multidisciplinary treatment regimen remains to be studied in the future in order to better define timing, doses, target volumes, and general need for RT in a particularly sensitive cohort of patients.
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Affiliation(s)
- Danny Jazmati
- Department of Particle Therapy, University Hospital Essen, West German Proton Therapy Centre Essen (WPE), West German Cancer Center (WTZ), Essen, Germany
| | - Sarina Butzer
- Children's Hospital, University of Cologne, Cologne, Germany
| | - Barbara Hero
- Children's Hospital, University of Cologne, Cologne, Germany
| | - Dalia Ahmad Khalil
- Department of Particle Therapy, University Hospital Essen, West German Proton Therapy Centre Essen (WPE), West German Cancer Center (WTZ), Essen, Germany
| | - Julien Merta
- Department of Particle Therapy, University Hospital Essen, West German Proton Therapy Centre Essen (WPE), West German Cancer Center (WTZ), Essen, Germany
| | - Christian Bäumer
- Department of Particle Therapy, University Hospital Essen, West German Proton Therapy Centre Essen (WPE), West German Cancer Center (WTZ), Essen, Germany.,Faculty of Physics, TU Dortmund University, Dortmund, Germany.,Department of Particle Therapy, University Hospital Essen, West German Proton Therapy Centre Essen (WPE), West German Cancer Center (WTZ), German Cancer Consortium (DKTK), Essen, Germany
| | - Gina Plum
- Children's Hospital, University of Cologne, Cologne, Germany
| | - Jörg Fuchs
- Department of Pediatric Surgery and Pediatric Urology, University Children's Hospital Tuebingen, Tübingen, Germany
| | | | - Theresa Steinmeier
- Department of Particle Therapy, University Hospital Essen, West German Proton Therapy Centre Essen (WPE), West German Cancer Center (WTZ), Essen, Germany
| | - Sarah Peters
- Department of Particle Therapy, University Hospital Essen, West German Proton Therapy Centre Essen (WPE), West German Cancer Center (WTZ), Essen, Germany
| | - Jerome Doyen
- Department of Particle Therapy, University Hospital Essen, West German Proton Therapy Centre Essen (WPE), West German Cancer Center (WTZ), Essen, Germany
| | - Theresa Thole
- Department of Pediatric Oncology/Hematology, Charité-Universitätsmedizin Berlin, Berlin, Germany
| | - Matthias Schmidt
- Department of Nuclear Medicine, University Hospital of Cologne, Cologne, Germany
| | | | - Stephan Tippelt
- University Hospital of Essen, Paediatrics III, Paediatric Haematology and Oncology, Essen, Germany
| | - Angelika Eggert
- Department of Pediatric Oncology/Hematology, Charité-Universitätsmedizin Berlin, Berlin, Germany
| | - Rudolf Schwarz
- Department of Radiotherapy and Radiooncology, Outpatient Center, University Medical Center Hamburg-Eppendorf, Hamburg, Germany
| | - Thorsten Simon
- Children's Hospital, University of Cologne, Cologne, Germany
| | - Beate Timmermann
- Department of Particle Therapy, University Hospital Essen, West German Proton Therapy Centre Essen (WPE), West German Cancer Center (WTZ), Essen, Germany.,Department of Particle Therapy, University Hospital Essen, West German Proton Therapy Centre Essen (WPE), West German Cancer Center (WTZ), German Cancer Consortium (DKTK), Essen, Germany
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7
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Fattori G, Hrbacek J, Regele H, Bula C, Mayor A, Danuser S, Oxley DC, Rechsteiner U, Grossmann M, Via R, Böhlen TT, Bolsi A, Walser M, Togno M, Colvill E, Lempen D, Weber DC, Lomax AJ, Safai S. Commissioning and quality assurance of a novel solution for respiratory-gated PBS proton therapy based on optical tracking of surface markers. Z Med Phys 2020; 32:52-62. [PMID: 32830006 PMCID: PMC9948868 DOI: 10.1016/j.zemedi.2020.07.001] [Citation(s) in RCA: 13] [Impact Index Per Article: 3.3] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/21/2020] [Revised: 06/01/2020] [Accepted: 07/10/2020] [Indexed: 12/15/2022]
Abstract
We present the commissioning and quality assurance of our clinical protocol for respiratory gating in pencil beam scanning proton therapy for cancer patients with moving targets. In a novel approach, optical tracking has been integrated in the therapy workflow and used to monitor respiratory motion from multiple surrogates, applied on the patients' chest. The gating system was tested under a variety of experimental conditions, specific to proton therapy, to evaluate reaction time and reproducibility of dose delivery control. The system proved to be precise in the application of beam gating and allowed the mitigation of dose distortions even for large (1.4cm) motion amplitudes, provided that adequate treatment windows were selected. The total delivered dose was not affected by the use of gating, with measured integral error within 0.15cGy. Analysing high-resolution images of proton transmission, we observed negligible discrepancies in the geometric location of the dose as a function of the treatment window, with gamma pass rate greater than 95% (2%/2mm) compared to stationary conditions. Similarly, pass rate for the latter metric at the 3%/3mm level was observed above 97% for clinical treatment fields, limiting residual movement to 3mm at end-exhale. These results were confirmed in realistic clinical conditions using an anthropomorphic breathing phantom, reporting a similarly high 3%/3mm pass rate, above 98% and 94%, for regular and irregular breathing, respectively. Finally, early results from periodic QA tests of the optical tracker have shown a reliable system, with small variance observed in static and dynamic measurements.
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Affiliation(s)
- Giovanni Fattori
- Center for Proton Therapy, Paul Scherrer Institute, 5232 Villigen, Switzerland.
| | - Jan Hrbacek
- Center for Proton Therapy, Paul Scherrer Institute, 5232 Villigen, Switzerland
| | - Harald Regele
- Center for Proton Therapy, Paul Scherrer Institute, 5232 Villigen, Switzerland
| | - Christian Bula
- Center for Proton Therapy, Paul Scherrer Institute, 5232 Villigen, Switzerland
| | - Alexandre Mayor
- Center for Proton Therapy, Paul Scherrer Institute, 5232 Villigen, Switzerland
| | - Stefan Danuser
- Center for Proton Therapy, Paul Scherrer Institute, 5232 Villigen, Switzerland
| | - David C. Oxley
- Center for Proton Therapy, Paul Scherrer Institute, 5232 Villigen, Switzerland
| | - Urs Rechsteiner
- Center for Proton Therapy, Paul Scherrer Institute, 5232 Villigen, Switzerland
| | - Martin Grossmann
- Center for Proton Therapy, Paul Scherrer Institute, 5232 Villigen, Switzerland
| | - Riccardo Via
- Center for Proton Therapy, Paul Scherrer Institute, 5232 Villigen, Switzerland
| | - Till T. Böhlen
- Center for Proton Therapy, Paul Scherrer Institute, 5232 Villigen, Switzerland
| | - Alessandra Bolsi
- Center for Proton Therapy, Paul Scherrer Institute, 5232 Villigen, Switzerland
| | - Marc Walser
- Center for Proton Therapy, Paul Scherrer Institute, 5232 Villigen, Switzerland
| | - Michele Togno
- Center for Proton Therapy, Paul Scherrer Institute, 5232 Villigen, Switzerland
| | - Emma Colvill
- Center for Proton Therapy, Paul Scherrer Institute, 5232 Villigen, Switzerland
| | - Daniel Lempen
- Center for Proton Therapy, Paul Scherrer Institute, 5232 Villigen, Switzerland
| | - Damien C. Weber
- Center for Proton Therapy, Paul Scherrer Institute, 5232 Villigen, Switzerland,Department of Radiation Oncology, University Hospital Zurich, 8091 Zurich, Switzerland,Department of Radiation Oncology, University Hospital Bern, 3000 Bern, Switzerland
| | - Antony J. Lomax
- Center for Proton Therapy, Paul Scherrer Institute, 5232 Villigen, Switzerland,Department of Physics, ETH Zurich, 8092 Zurich, Switzerland
| | - Sairos Safai
- Center for Proton Therapy, Paul Scherrer Institute, 5232 Villigen, Switzerland
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