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Wulff J, Paul A, Bäcker CM, Baumann KS, Esser JN, Koska B, Timmermann B, Verbeek NG, Bäumer C. Consistency of Faraday cup and ionization chamber dosimetry of proton fields and the role of nuclear interactions. Med Phys 2024; 51:2277-2292. [PMID: 37991110 DOI: 10.1002/mp.16819] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/13/2023] [Revised: 09/21/2023] [Accepted: 09/28/2023] [Indexed: 11/23/2023] Open
Abstract
BACKGROUND A Faraday cup (FC) facilitates a quite clean measurement of the proton fluence emerging from clinical spot-scanning nozzles with narrow pencil-beams. The utilization of FCs appears to be an attractive option for high dose rate delivery modes and the source models of Monte-Carlo (MC) dose engines. However, previous studies revealed discrepancies of 3%-6% between reference dosimetry with ionization chambers (ICs) and FC-based dosimetry. This has prevented the widespread use of FCs for dosimetry in proton therapy. PURPOSE The current study aims at bridging the gap between FC dosimetry and IC dosimetry of proton fields delivered with spot-scanning treatment heads. Particularly, a novel method to evaluate FC measurements is introduced. METHODS A consistency check is formulated, which makes use of the energy balance and the reciprocity theorem. The measurement data comprise central-axis depth distributions of the absorbed dose of quasi-monochromatic fields with a width of about 28.5 cm and FC measurements of the reciprocal fields with a single spot. These data are complemented by a look-up of energy-range tables, the average Q-value of transmutations, and the escape energy carried away by neutrons and photons. The latter data are computed by MC simulations, which in turn are validated with measurements of the distal dose tail and neutron out-of-field doses. For comparison, the conventional approach of FC evaluation is performed, which computes absorbed dose from the product of fluence and stopping power. The results from the FC measurements are compared with the standard dosimetry protocols and improved reference dosimetry methods. RESULTS The deviation between the conventional FC-based dosimetry and the IC-based one according to standard dosimetry protocols was -4.7 ( ± $\pm$ 3.3)% for a 100 MeV field and -3.6 ( ± $\pm$ 3.5)% for 200 MeV, thereby agreeing within the reported uncertainties. The deviations could be reduced to -4.0 ( ± $\pm$ 2.9)% and -3.0 ( ± $\pm$ 3.1)% by adopting state-of-the-art reference dosimetry methods. The alternative approach using the energy balance gave deviations of only -1.9% (100 MeV) and -2.6% (200 MeV) using state-of-the-art dosimetry. The standard uncertainty of this novel approach was estimated to be about 2%. CONCLUSIONS An alternative concept has been established to determine the absorbed dose of monoenergetic proton fields with an FC. It eliminates the strong dependence of the conventional FC-based approach on the MC simulation of the stopping-power and of the secondary ions, which according to the study at hand is the major contributor to the underestimation of the absorbed dose. Some contributions to the uncertainty of the novel approach could potentially be reduced in future studies. This would allow for accurate consistency tests of conventional dosimetry procedures.
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Affiliation(s)
- Jörg Wulff
- West German Proton Therapy Centre Essen, Essen, Germany
- University Hospital Essen, Essen, Germany
- West German Cancer Center (WTZ), Essen, Germany
| | - Anne Paul
- West German Proton Therapy Centre Essen, Essen, Germany
- University Hospital Essen, Essen, Germany
- West German Cancer Center (WTZ), Essen, Germany
- Heinrich Heine University Düsseldorf, Düsseldorf, Germany
| | - Claus Maximilian Bäcker
- West German Proton Therapy Centre Essen, Essen, Germany
- University Hospital Essen, Essen, Germany
- West German Cancer Center (WTZ), Essen, Germany
| | - Kilian-Simon Baumann
- Department of Radiotherapy and Radiation Oncology, Marburg University Hospital, Marburg, Germany
- Marburg Ion-Beam Therapy Center (MIT), Marburg, Germany
- University of Applied Sciences, Institute of Medical Physics and Radiation Protection, Giessen, Germany
| | - Johannes Niklas Esser
- West German Proton Therapy Centre Essen, Essen, Germany
- University Hospital Essen, Essen, Germany
- West German Cancer Center (WTZ), Essen, Germany
| | - Benjamin Koska
- West German Proton Therapy Centre Essen, Essen, Germany
- University Hospital Essen, Essen, Germany
- West German Cancer Center (WTZ), Essen, Germany
| | - Beate Timmermann
- West German Proton Therapy Centre Essen, Essen, Germany
- University Hospital Essen, Essen, Germany
- West German Cancer Center (WTZ), Essen, Germany
- Heinrich Heine University Düsseldorf, Düsseldorf, Germany
- German Cancer Consortium (DKTK), Essen, Germany
- Department of Particle Therapy, University Hospital Essen, Essen, Germany
| | - Nico Gerd Verbeek
- West German Proton Therapy Centre Essen, Essen, Germany
- University Hospital Essen, Essen, Germany
- West German Cancer Center (WTZ), Essen, Germany
| | - Christian Bäumer
- West German Proton Therapy Centre Essen, Essen, Germany
- University Hospital Essen, Essen, Germany
- West German Cancer Center (WTZ), Essen, Germany
- German Cancer Consortium (DKTK), Essen, Germany
- Department of Physics, Technische Universität Dortmund, Dortmund, Germany
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Ehwald J, Togno M, Lomax AJ, Weber DC, Safai S, Winterhalter C. Detailed Monte-Carlo characterization of a Faraday cup for proton therapy. Med Phys 2023; 50:5828-5841. [PMID: 37227735 DOI: 10.1002/mp.16464] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/07/2022] [Revised: 04/03/2023] [Accepted: 04/09/2023] [Indexed: 05/26/2023] Open
Abstract
BACKGROUND Experiments with ultra-high dose rates in proton therapy are of increasing interest for potential treatment benefits. The Faraday Cup (FC) is an important detector for the dosimetry of such ultra-high dose rate beams. So far, there is no consensus on the optimal design of a FC, or on the influence of beam properties and magnetic fields on shielding of the FC from secondary charged particles. PURPOSE To perform detailed Monte Carlo simulations of a Faraday cup to identify and quantify all the charge contributions from primary protons and secondary particles that modify the efficiency of the FC response as a function of a magnetic field employed to improve the detector's reading. METHODS In this paper, a Monte Carlo (MC) approach was used to investigate the Paul Scherrer Institute (PSI) FC and quantify contributions of charged particles to its signal for beam energies of 70, 150, and 228 MeV and magnetic fields between 0 and 25 mT. Finally, we compared our MC simulations to measurements of the response of the PSI FC. RESULTS For maximum magnetic fields, the efficiency (signal of the FC normalized to charged delivered by protons) of the PSI FC varied between 99.97% and 100.22% for the lowest and highest beam energy. We have shown that this beam energy-dependence is mainly caused by contributions of secondary charged particles, which cannot be fully suppressed by the magnetic field. Additionally, it has been demonstrated that these contributions persist, making the FC efficiency beam energy dependent for fields up to 250 mT, posing inevitable limits on the accuracy of FC measurements if not corrected. In particular, we have identified a so far unreported loss of electrons via the outer surfaces of the absorber block and show the energy distributions of secondary electrons ejected from the vacuum window (VW) (up to several hundred keV), together with electrons ejected from the absorber block (up to several MeV). Even though, in general, simulations and measurements were well in agreement, the limitation of the current MC calculations to produce secondary electrons below 990 eV posed a limit in the efficiency simulations in the absence of a magnetic field as compared to the experimental data. CONCLUSION TOPAS-based MC simulations allowed to identify various and previously unreported contributions to the FC signal, which are likely to be present in other FC designs. Estimating the beam energy dependence of the PSI FC for additional beam energies could allow for the implementation of an energy-dependent correction factor to the signal. Dose estimates, based on accurate measurements of the number of delivered protons, provided a valid instrument to challenge the dose determined by reference ionization chambers, not only at ultra-high dose rates but also at conventional dose rates.
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Affiliation(s)
- Julian Ehwald
- Centre for Proton Therapy, Paul Scherrer Institute, Villigen PSI, Switzerland
- Department of Physics, ETH Zurich, Zurich, Switzerland
| | - Michele Togno
- Centre for Proton Therapy, Paul Scherrer Institute, Villigen PSI, Switzerland
| | - Antony John Lomax
- Centre for Proton Therapy, Paul Scherrer Institute, Villigen PSI, Switzerland
- Department of Physics, ETH Zurich, Zurich, Switzerland
| | - Damien Charles Weber
- Centre for Proton Therapy, Paul Scherrer Institute, Villigen PSI, Switzerland
- Radiation Oncology Department of University Hospital of Bern, Bern, Switzerland
- Radiation Oncology Department of University Hospital of Zurich, Zurich, Switzerland
| | - Sairos Safai
- Centre for Proton Therapy, Paul Scherrer Institute, Villigen PSI, Switzerland
| | - Carla Winterhalter
- Centre for Proton Therapy, Paul Scherrer Institute, Villigen PSI, Switzerland
- Department of Physics, ETH Zurich, Zurich, Switzerland
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Singh RP, Patel DN, Thareja RK. Investigation of ion dynamics of laser ablated single and colliding carbon plasmas using Faraday cup. Heliyon 2022; 8:e10621. [PMID: 36164541 PMCID: PMC9508419 DOI: 10.1016/j.heliyon.2022.e10621] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/26/2022] [Revised: 08/03/2022] [Accepted: 09/08/2022] [Indexed: 11/29/2022] Open
Abstract
We report a comparative study of a single plasma and a colliding laser produced plasma, investigated using a Faraday cup. An enhancement in ion emission and stagnation is observed in colliding plasma plume compared to single plasma plume. We observed that fast ion generation in laser ablated plasma can be achieved at large laser intensity on to the target. As laser intensity increases ionic yield increases for both colliding and single plume and at a fixed laser intensity ionic yield decreases with increase in ambient pressure. The double peak structure is observed in the ion signal at large fluence where the peaks correspond to fast and slow species. A Faraday cup composed of nine collectors is used to measure the spatial/angular distribution of ion of expanding plasma plume. Ionic yield is found to be larger in the colliding plasma plume than the single plasma plume at all spatial/angular positions.
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Affiliation(s)
- Ravi Pratap Singh
- Department of Physics, Indian Institute of Technology, Kanpur, India.,Rajkiya Engineering College Sonbhadra, Uttar Pradesh, India
| | - D N Patel
- Department of Physics, Indian Institute of Technology, Kanpur, India.,Micron Memory Taiwan, Houli District, Taichung City, Taiwan
| | - Raj K Thareja
- Department of Physics, Indian Institute of Technology, Kanpur, India
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Winterhalter C, Togno M, Nesteruk KP, Emert F, Psoroulas S, Vidal M, Meer D, Weber DC, Lomax A, Safai S. Faraday cup for commissioning and quality assurance for proton pencil beam scanning beams at conventional and ultra-high dose rates. Phys Med Biol 2021; 66. [PMID: 33906166 DOI: 10.1088/1361-6560/abfbf2] [Citation(s) in RCA: 7] [Impact Index Per Article: 2.3] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/17/2020] [Accepted: 04/27/2021] [Indexed: 11/11/2022]
Abstract
Recently, proton therapy treatments delivered with ultra-high dose rates have been of high scientific interest, and the Faraday cup (FC) is a promising dosimetry tool for such experiments. Different institutes use different FC designs, and either a high voltage guard ring, or the combination of an electric and a magnetic field is employed to minimize the effect of secondary electrons. The authors first investigate these different approaches for beam energies of 70, 150, 230 and 250 MeV, magnetic fields between 0 and 24 mT and voltages between -1000 and 1000 V. When applying a magnetic field, the measured signal is independent of the guard ring voltage, indicating that this setting minimizes the effect of secondary electrons on the reading of the FC. Without magnetic field, applying the negative voltage however decreases the signal by an energy dependent factor up to 1.3% for the lowest energy tested and 0.4% for the highest energy, showing an energy dependent response. Next, the study demonstrates the application of the FC up to ultra-high dose rates. FC measurements with cyclotron currents up to 800 nA (dose rates of up to approximately 1000 Gy s-1) show that the FC is indeed dose rate independent. Then, the FC is applied to commission the primary gantry monitor for high dose rates. Finally, short-term reproducibility of the monitor calibration is quantified within single days, showing a standard deviation of 0.1% (one sigma). In conclusion, the FC is a promising, dose rate independent tool for dosimetry up to ultra-high dose rates. Caution is however necessary when using a FC without magnetic field, as a guard ring with high voltage alone can introduce an energy dependent signal offset.
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Affiliation(s)
- C Winterhalter
- Centre for Proton Therapy, Paul Scherrer Institute, Switzerland.,Physics Department, ETH Zurich, Switzerland
| | - M Togno
- Centre for Proton Therapy, Paul Scherrer Institute, Switzerland
| | - K P Nesteruk
- Centre for Proton Therapy, Paul Scherrer Institute, Switzerland
| | - F Emert
- Centre for Proton Therapy, Paul Scherrer Institute, Switzerland
| | - S Psoroulas
- Centre for Proton Therapy, Paul Scherrer Institute, Switzerland
| | - M Vidal
- Institut Mediterraneen de Protontherapie, Centre Antoine Lacassagne, Nice, France
| | - D Meer
- Centre for Proton Therapy, Paul Scherrer Institute, Switzerland
| | - D C Weber
- Centre for Proton Therapy, Paul Scherrer Institute, Switzerland.,Radiation Oncology Department of the University Hospital of Bern, Switzerland.,Radiation Oncology Department of the University Hospital of Zürich, Switzerland
| | - A Lomax
- Centre for Proton Therapy, Paul Scherrer Institute, Switzerland.,Physics Department, ETH Zurich, Switzerland
| | - S Safai
- Centre for Proton Therapy, Paul Scherrer Institute, Switzerland
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Lian H, Ding K, Wu Y, Chen Y, Li J, Li H. [Development of the Extraction Reference Point Beam Diagnostic System for Proton Medical Accelerator]. Zhongguo Yi Liao Qi Xie Za Zhi 2019; 43:102-105. [PMID: 30977605 DOI: 10.3969/j.issn.1671-7104.2019.02.007] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Key Words] [MESH Headings] [Subscribe] [Scholar Register] [Indexed: 06/09/2023]
Abstract
er to detect the beam quality of the SC200 superconducting cyclotron,measure the beam at the extraction reference and the acceptance of the accelerator is realized.This article mainly introduces the design that use the scintillation screen at the extraction reference to measure the beam profile,position and use the Faraday cup to measure the current intensity with 2.5 level accuracy.The remoted controlling of probes and the acquisition and processing of signal based on LabVIEW and PLC.
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Affiliation(s)
- Huan Lian
- Institute of Plasma Physics, Chinese Academy of Sciences, Hefei, 230031
- University of Science and Technology of China, Hefei, 230026
| | - Kaizhong Ding
- Institute of Plasma Physics, Chinese Academy of Sciences, Hefei, 230031
| | - Yucheng Wu
- Hefei CAS Ion Medical and Technical Devices Co Ltd, Hefei, 230031
| | - Yonghua Chen
- Institute of Plasma Physics, Chinese Academy of Sciences, Hefei, 230031
| | - Junjun Li
- Institute of Plasma Physics, Chinese Academy of Sciences, Hefei, 230031
| | - Han Li
- Institute of Plasma Physics, Chinese Academy of Sciences, Hefei, 230031
- University of Science and Technology of China, Hefei, 230026
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