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Muir B, Davis S, Dhanesar S, Hillman Y, Iakovenko V, Kim GGY, Alves VGL, Lei Y, Lowenstein J, Renaud J, Sarfehnia A, Siebers J, Tantôt L. AAPM WGTG51 Report 385: Addendum to the AAPM's TG-51 protocol for clinical reference dosimetry of high-energy electron beams. Med Phys 2024. [PMID: 38980220 DOI: 10.1002/mp.17277] [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: 12/08/2023] [Revised: 03/29/2024] [Accepted: 06/14/2024] [Indexed: 07/10/2024] Open
Abstract
An Addendum to the AAPM's TG-51 protocol for the determination of absorbed dose to water is presented for electron beams with energies between 4 MeV and 22 MeV (1.70 cm ≤ R 50 ≤ 8.70 cm $1.70\nobreakspace {\rm cm} \le R_{\text{50}} \le 8.70\nobreakspace {\rm cm}$ ). This updated formalism allows simplified calibration procedures, including the use of calibrated cylindrical ionization chambers in all electron beams without the use of a gradient correction. Newk Q $k_{Q}$ data are provided for electron beams based on Monte Carlo simulations. Implementation guidance is provided. Components of the uncertainty budget in determining absorbed dose to water at the reference depth are discussed. Specifications for a reference-class chamber in electron beams include chamber stability, settling, ion recombination behavior, and polarity dependence. Progress in electron beam reference dosimetry is reviewed. Although this report introduces some major changes (e.g., gradient corrections are implicitly included in the electron beam quality conversion factors), they serve to simplify the calibration procedure. Results for absorbed dose per linac monitor unit are expected to be up to approximately 2 % higher using this Addendum compared to using the original TG-51 protocol.
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Affiliation(s)
- Bryan Muir
- Metrology Research Centre, National Research Council of Canada, Ottawa, Ontario, Canada
| | - Stephen Davis
- Department of Radiation Oncology, Miami Cancer Institute, Miami, Florida, USA
| | - Sandeep Dhanesar
- Department of Radiation Oncology, Houston Methodist Hospital, Houston, Texa, USA
| | - Yair Hillman
- Department of Radiation Oncology, Sharett Institute of Oncology, Hadassah Medical Center, Hebrew University of Jerusalem, Jerusalem, Israel
| | | | - Grace Gwe-Ya Kim
- Department of Radiation Medicine and Applied Sciences, UC San Diego School of Medicine, San Diego, California, USA
| | | | - Yu Lei
- Department of Radiation Oncology, University of Nebraska Medical Center, Omaha, Nebraska, USA
| | - Jessica Lowenstein
- Department of Radiation Physics, UT M.D. Anderson Cancer Center, Houston, Texa, USA
| | - James Renaud
- Metrology Research Centre, National Research Council of Canada, Ottawa, Ontario, Canada
| | - Arman Sarfehnia
- Department of Radiation Oncology, University of Toronto, Toronto, ON, Canada
- Department of Medical Physics, Odette Cancer Centre, Sunnybrook Health Sciences Centre, Toronto, Ontario, Canada
| | - Jeffrey Siebers
- Department of Radiation Oncology, University of Virginia, Charlottesville, Virginia, USA
| | - Laurent Tantôt
- Département de radio-oncologie, CIUSSS de l'Est-de-l'Île-de-Montréal - Hôpital Maisonneuve-Rosemont, Montreal, Quebec, Canada
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Alissa M, Zink K, Röser A, Flatten V, Schoenfeld AA, Czarnecki D. Monte Carlo calculated beam quality correction factors for high energy electron beams. Phys Med 2024; 117:103179. [PMID: 38042061 DOI: 10.1016/j.ejmp.2023.103179] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 01/19/2023] [Revised: 10/05/2023] [Accepted: 11/16/2023] [Indexed: 12/04/2023] Open
Abstract
PURPOSE As the dosimetry protocol TRS 398 is being revised and the ICRU report 90 provides new recommendations for density correction as well as the mean ionization energies of water and graphite, updated beam quality correction factors kQ are calculated for reference dosimetry in electron beams and for independent validation of previously determined values. METHODS Monte Carlo simulations have been performed using EGSnrc to calculate the absorbed dose to water and the dose to the active volumes of ionization chambers SNC600c, SNC125c and SNC350p (all Sun Nuclear, A Mirion Medical Company, Melbourne, FL). Realistic clinical electron beam spectra were used to cover the entire energy range of therapeutic electron accelerators. The Monte Carlo simulations were validated by measurements on a clinical linear accelerator. With regards to the cylindrical chambers, the simulations were performed according to the setup recommendations of TRS 398 and AAPM TG 51, i.e. with and without consideration of a reference point shift by rcav/2. RESULTS kQ values as a function of the respective beam quality specifier R50 were fitted by recommended equations for electron beam dosimetry in the range of 5 MeV to 18 MeV. The fitting curves to the calculated values showed a root mean square deviation between 0.0016 and 0.0024. CONCLUSION Electron beam quality correction factors kQ were calculated by Monte Carlo simulations for the cylindrical ionization chambers SNC600c and SNC125c as well as the plane parallel ionization chamber SNC350p to provide updated data for the TRS 398 and TG 51 dosimetry protocols.
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Affiliation(s)
- Mohamad Alissa
- Institute of Medical Physics and Radiation Protection, University of Applied Sciences Giessen (THM), Wiesenstraße 14, Giessen, 35390, Germany
| | - Klemens Zink
- Institute of Medical Physics and Radiation Protection, University of Applied Sciences Giessen (THM), Wiesenstraße 14, Giessen, 35390, Germany; Department of Radiotherapy and Radiation Oncology, University Medical Center Giessen and Marburg, Baldingerstraße, Marburg, 35043, Germany
| | - Arnd Röser
- Helios Universitätsklinikum Wuppertal, Heusnerstraße 40, Wuppertal, 42283, Germany
| | - Veronika Flatten
- Sun Nuclear, A Mirion Medical Company, 3275 Suntree Blvd, Melbourne, 32940, FL, USA
| | - Andreas A Schoenfeld
- Sun Nuclear, A Mirion Medical Company, 3275 Suntree Blvd, Melbourne, 32940, FL, USA
| | - Damian Czarnecki
- Institute of Medical Physics and Radiation Protection, University of Applied Sciences Giessen (THM), Wiesenstraße 14, Giessen, 35390, Germany.
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Mahfirotin DA, Ferliano B, Handika AD, Asril YS, Fadli M, Ryangga D, Nelly N, Kurniawan E, Wibowo WE, Yadav P, Pawiro SA. A multicenter study of modified electron beam output calibration. J Appl Clin Med Phys 2024; 25:e14232. [PMID: 38088260 PMCID: PMC10795448 DOI: 10.1002/acm2.14232] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/28/2023] [Revised: 11/13/2023] [Accepted: 11/19/2023] [Indexed: 01/19/2024] Open
Abstract
PURPOSE This study aims to assess the accuracy of a modified electron beam calibration based on the IAEA TRS-398 and AAPM-TG-51 in multicenter radiotherapy. METHODS This study was performed using the Elekta and Varian Linear Accelerator electron beams with energies of 4-22 MeV under reference conditions using cylindrical (PTW 30013, IBA FC65-G, and IBA FC65-P) and parallel-plate (PTW 34045, PTW 34001, and IBA PPC-40) chambers. The modified calibration used a cylindrical chamber and an updatedk ' Q $k{^{\prime}}_Q$ based on Monte Carlo calculations, whereas TRS-398 and TG-51 used cylindrical and parallel-plate chambers for reference dosimetry. The dose ratio of the modified calibration procedure, TRS-398 and TG-51 were obtained by comparing the dose at the maximum depth of the modified calibration to TRS-398 and TG-51. RESULTS The study found that all cylindrical chambers' beam quality conversion factors determined with the modified calibration( k ' Q ) $( {{{k^{\prime}}}_Q} )$ to the TRS-398 and TG-51 vary from 0.994 to 1.003 and 1.000 to 1.010, respectively. The dose ratio of modified/TRS-398cyl and modified/TRS-398parallel-plate, the variation ranges were 0.980-1.014 and 0.981-1.019, while for the counterpart modified/TG-51cyl was found varying between 0.991 and 1.017 and the ratio of modified/TG-51parallel-plate varied in the range of 0.981-1.019. CONCLUSION This multi-institutional study analyzed a modified calibration procedure utilizing new data for electron beam calibrations at multiple institutions and evaluated existing calibration protocols. Based on observed variations, the current calibration protocols should be updated with detailed metrics on the stability of linac components.
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Affiliation(s)
- Dwi Aprilia Mahfirotin
- Department of PhysicsFaculty of Mathematics and Natural SciencesUniversitas Indonesia, DepokWest JavaIndonesia
- Department of Radiation OncologyMitra Keluarga Bekasi Timur Hospital, BekasiWest JavaIndonesia
| | - Brian Ferliano
- Department of Radiation OncologyGading Pluit HospitalJakartaIndonesia
| | - Andrian Dede Handika
- Department of Radiation OncologyPersahabatan Central General HospitalJakartaIndonesia
| | - Yosi Sudarsi Asril
- Department of Radiation OncologyMayapada Hospital Jakarta SelatanJakartaIndonesia
| | - Muhamad Fadli
- Department of Radiation OncologyMRCCC Siloam Hospital SemanggiJakartaIndonesia
| | - Dea Ryangga
- Department of Radiation OncologyPasar Minggu Regional HospitalJakartaIndonesia
| | - Nelly Nelly
- Department of Radiation OncologySiloam Hospital TB SimatupangJakartaIndonesia
| | - Eddy Kurniawan
- Department of Radiation OncologyTzu Chi HospitalJakartaIndonesia
| | - Wahyu Edy Wibowo
- Department of Radiation OncologyDr. Cipto Mangunkusumo National General Hospital CentralFaculty of MedicineUniversitas IndonesiaJakartaIndonesia
| | - Poonam Yadav
- Department of Radiation OncologyNorthwestern Memorial HospitalNorthwestern University Feinberg School of MedicineChicagoIllinoisUSA
| | - Supriyanto Ardjo Pawiro
- Department of PhysicsFaculty of Mathematics and Natural SciencesUniversitas Indonesia, DepokWest JavaIndonesia
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Elbashir FEM, Ksouri W, Eisa MH, Alanazi S, Habbani F, Sulieman A, Bradley DA, Suliman II. Comparison of Dosimetry Protocols for Electron Beam Radiotherapy Calibrations and Measurement Uncertainties. Life (Basel) 2021; 12:life12010031. [PMID: 35054424 PMCID: PMC8781094 DOI: 10.3390/life12010031] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/24/2021] [Revised: 12/21/2021] [Accepted: 12/22/2021] [Indexed: 11/16/2022] Open
Abstract
This paper presents guidelines for the calibration of radiation beams that were issued by the International Atomic Energy Agency (IAEA TRS 398), the American Association of Physicists in Medicine (AAPM TG 51) and the German task group (DIN 6800-2). These protocols are based on the use of an ionization chamber calibrated in terms of absorbed dose to water in a standard laboratory’s reference quality beam, where the previous protocols were based on air kerma standards. This study aims to determine uncertainties in dosimetry for electron beam radiotherapy using internationally established high-energy radiotherapy beam calibration standards. Methods: Dw was determined in 6-, 12- and 18 MeV electron energies under reference conditions using three cylindrical and two plane-parallel ion chambers in concert with the IAEA TRS 398, AAPM TG 51 and DIN 6800-2 absorbed dose protocols. From mean measured Dw values, the ratio TRS 398/TG 51 was found to vary between 0.988 and 1.004, while for the counterpart TRS 398/DIN 6800-2 and TG 51/DIN 6800-2, the variation ranges were 0.991–1.003 and 0.997–1.005, respectively. For the cylindrical chambers, the relative combined uncertainty (k = 1) in absorbed dose measurements was 1.44%, while for the plane-parallel chambers, it ranged from 1.53 to 1.88%. Conclusions: A high degree of consistency was demonstrated among the three protocols. It is suggested that in the use of the presently determined dose conversion factors across the three protocols, dose intercomparisons can be facilitated between radiotherapy centres.
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Affiliation(s)
- Fawzia E. M. Elbashir
- Department of Medical Physics, National Cancer Institute, University of Gezira, Wad Madani P.O. Box 1111, Sudan;
| | - Wassim Ksouri
- Department of Medical Physics, Centre de Radiothérapie Hartmann 4, Rue Kleber, CS90004, CEDEX, 92309 Levallois-Perret, France;
| | - Mohamed Hassan Eisa
- Department of Physics, College of Science, Imam Mohammad Ibn Saud Islamic University (IMSIU), Riyadh 11642, Saudi Arabia; (M.H.E.); (S.A.)
| | - Sitah Alanazi
- Department of Physics, College of Science, Imam Mohammad Ibn Saud Islamic University (IMSIU), Riyadh 11642, Saudi Arabia; (M.H.E.); (S.A.)
| | - Farouk Habbani
- Department of Physics, Faculty of Science, University of Khartoum, Khartoum P.O. Box 321, Sudan;
| | - Abdelmoneim Sulieman
- Radiology and Medical Imaging Department, College of Applied Medical Sciences, Prince Sattam bin Abdulaziz University, Alkharj 11942, Saudi Arabia;
| | - David A. Bradley
- Centre for Applied Physics and Radiation Technologies, School of Engineering and Technology, Sunway University, Bandar Sunway 47500, Selangor, Malaysia;
- Department of Physics, University of Surrey, Guildford GU2 7XH, UK
| | - Ibrahim I. Suliman
- Department of Physics, College of Science, Imam Mohammad Ibn Saud Islamic University (IMSIU), Riyadh 11642, Saudi Arabia; (M.H.E.); (S.A.)
- Radiation and Nuclear Safety Institute, Sudan Atomic Energy Commission, Khartoum P.O. Box 3001, Sudan
- Correspondence: ; Tel.: +966-5-3891-8127
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Ding GX. Stopping-power ratios for electron beams used in total skin electron therapy. Med Phys 2021; 48:5472-5478. [PMID: 34287969 DOI: 10.1002/mp.15121] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/23/2021] [Revised: 06/28/2021] [Accepted: 07/12/2021] [Indexed: 11/10/2022] Open
Abstract
PURPOSE The electron beams for total skin electron therapy (TSET) are often degraded by a scatter plate in addition to extended distances. For electron dosimetry, both the AAPM TG-51 and IAEA TRS-398 recommend the use of two formulas developed by Burns et al [Med. Phys. 23, 489-501 (1996)] to estimate the water-to-air stopping-power ratios (SPRs). Both formulas are based on a fit to SPRs calculated for standard electron beams. This study aims to find: (1) if the formulas are applicable to beams used in TSET and (2) the impact of the ICRU report 90 recommendations on the SPRs for these beams. METHODS The EGSnrc Monte Carlo code system is used to generate 6 MeV high dose rate total skin electron (HDTSe) beams used in TSET. The simulated beams are used to calculate dose distributions and SPRs as a function of depth in a water phantom. The fitted SPRs using the empirical formulas are compared with MC-calculated SPRs. RESULTS The electron beam quality specifier, the depth in water at which the absorbed dose falls to 50% of its maximum value, R50 , decreases approximately 1 mm for each additional 100-cm extended distance ranging from 2.24 cm at SSD = 100 to 1.72 cm at SSD = 700 cm. For beams passing through a scatter plate, R50 is 1.76 cm (1.14) at SSD = 300 and 1.48 cm (0.85 cm) at SSD = 600 cm with an Acrylic plate thickness of 3 mm (9 mm), respectively. The discrepancy between fitted and MC-calculated SPRs at dref as a function of R50 is <0.8%, and in many cases <0.4%. The difference between fitted and MC-calculated SPRs as a function of depth and R50 is within 1% at depths <0.8R50 for beams with R50 ≥ 1.14 cm. The ICRU-90 recommendations decrease SPRs by 0.3%-0.4% compared to the use of data recommended in ICRU-37. CONCLUSION The formulas used by the major protocols are accurate enough for clinical beams used in TSET and the error caused using the formulas is <1% to estimate SPRs as a function of depth and R50 for depths <0.8R50 for beams used in TSET with R50 ≥ 1.14 cm. The impact of the ICRU-90 recommendations shows a decrease of SPRs by a fraction of a percent for beams used in TSET.
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Affiliation(s)
- George X Ding
- Department of Radiation Oncology, Vanderbilt University School of Medicine, Nashville, Tennessee, USA
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Winkler P, Odreitz-Stark S, Haas E, Thalhammer M, Partl R. Commissioning, dosimetric characterization and machine performance assessment of the LIAC HWL mobile accelerator for Intraoperative Radiotherapy. Z Med Phys 2020; 30:279-288. [PMID: 32682654 DOI: 10.1016/j.zemedi.2020.06.004] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/02/2020] [Revised: 05/15/2020] [Accepted: 06/03/2020] [Indexed: 01/25/2023]
Abstract
BACKGROUND The LIAC HWL (Sordina IORT Technologies, Vicenza, Italy) is a recently designed mobile linear accelerator for intraoperative electron radiotherapy (IOeRT), producing high dose rate electron beams at four different energy levels. It features a software tool for the visualization of 2D dose distributions, which is based on Monte Carlo simulations. The aims of this work were to (i) assess the dosimetric characteristics of the accelerator, (ii) experimentally verify calculated data exported from the software and (iii) report on commissioning as well as performance of the system during the first year of operation. METHODS The electron energies of the LIAC HWL used in this study are 6, 8, 10 and 12 MeV. Diameters of the cylindrically shaped applicators range from 3 to 10cm. We studied two applicator sets with different length ratios of proximal and terminal applicator sections. Reference dosimetry, linearity as well as short- and long-term stability were measured with a PTW Advanced Markus chamber, relative depth dose and profiles were measured using an unshielded diode. Percentage-depth-dose (PDD) and transversal dose profile (TDP) data were exported from the simulation software LIACSim and compared with our measurements. RESULTS The device reaches dose rates up to 40Gy/min (for 12 MeV). Surface doses for the 10cm applicators are higher than 90%, X-ray background is below 0.6% for all energies. Simulations and measurements of PDD agreed well, with a maximum difference in the depth of the 50% isodose of 0.7mm for the flat-ended applicators and 1mm for the beveled applicators. The simulations slightly underestimate the dose in the lateral parts of the field (difference < 1.8% for flat-ended applicators). The two different applicator sets were dosimetrically equivalent. Long-term stability measurements for the first year of operation ranged from -2.1% to 1.6% (mean: -0.1%). CONCLUSIONS The system is dosimetrically well suited for IOeRT and performed stably and reliably. The software tool for visualization of dose distributions can be used to support treatment planning, following thorough validation.
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Affiliation(s)
- Peter Winkler
- Department of Therapeutic Radiology and Oncology, Medical University of Graz, Auenbrugger Platz 32, A-8036 Graz, Austria.
| | - Stefan Odreitz-Stark
- Department of Therapeutic Radiology and Oncology, Medical University of Graz, Auenbrugger Platz 32, A-8036 Graz, Austria
| | - Eva Haas
- Department of Therapeutic Radiology and Oncology, Medical University of Graz, Auenbrugger Platz 32, A-8036 Graz, Austria
| | - Martin Thalhammer
- Department of Therapeutic Radiology and Oncology, Medical University of Graz, Auenbrugger Platz 32, A-8036 Graz, Austria
| | - Richard Partl
- Department of Therapeutic Radiology and Oncology, Medical University of Graz, Auenbrugger Platz 32, A-8036 Graz, Austria
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Kretschmer J, Dulkys A, Brodbek L, Stelljes TS, Looe HK, Poppe B. Monte Carlo simulated beam quality and perturbation correction factors for ionization chambers in monoenergetic proton beams. Med Phys 2020; 47:5890-5905. [DOI: 10.1002/mp.14499] [Citation(s) in RCA: 7] [Impact Index Per Article: 1.8] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/26/2020] [Revised: 08/19/2020] [Accepted: 09/08/2020] [Indexed: 11/11/2022] Open
Affiliation(s)
- Jana Kretschmer
- University Clinic for Medical Radiation Physics Medical Campus Pius HospitalCarl‐von‐Ossietzky University Oldenburg Germany
| | - Anna Dulkys
- University Clinic for Medical Radiation Physics Medical Campus Pius HospitalCarl‐von‐Ossietzky University Oldenburg Germany
- Department of Radiation Therapy Helios Clinics Schwerin Schwerin Germany
| | - Leonie Brodbek
- University Clinic for Medical Radiation Physics Medical Campus Pius HospitalCarl‐von‐Ossietzky University Oldenburg Germany
- Department of Radiation Oncology University Medical Center GroningenUniversity of Groningen Groningen The Netherlands
| | - Tenzin Sonam Stelljes
- University Clinic for Medical Radiation Physics Medical Campus Pius HospitalCarl‐von‐Ossietzky University Oldenburg Germany
| | - Hui Khee Looe
- University Clinic for Medical Radiation Physics Medical Campus Pius HospitalCarl‐von‐Ossietzky University Oldenburg Germany
| | - Björn Poppe
- University Clinic for Medical Radiation Physics Medical Campus Pius HospitalCarl‐von‐Ossietzky University Oldenburg Germany
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Baumann KS, Kaupa S, Bach C, Engenhart-Cabillic R, Zink K. Corrigendum: Monte Carlo calculation of beam quality correction factors in proton beams using TOPAS/GEANT4 (2020 Phys. Med. Biol. 65 055015). Phys Med Biol 2020. [DOI: 10.1088/1361-6560/ab8fc2] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/11/2022]
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Baumann KS, Kaupa S, Bach C, Engenhart-Cabillic R, Zink K. Monte Carlo calculation of beam quality correction factors in proton beams using TOPAS/GEANT4. ACTA ACUST UNITED AC 2020; 65:055015. [DOI: 10.1088/1361-6560/ab6e53] [Citation(s) in RCA: 12] [Impact Index Per Article: 3.0] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/12/2022]
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Muir BR. A modified formalism for electron beam reference dosimetry to improve the accuracy of linac output calibration. Med Phys 2020; 47:2267-2276. [PMID: 31985833 DOI: 10.1002/mp.14048] [Citation(s) in RCA: 6] [Impact Index Per Article: 1.5] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/15/2019] [Revised: 12/20/2019] [Accepted: 01/20/2020] [Indexed: 11/11/2022] Open
Abstract
PURPOSE To present and demonstrate the accuracy of a modified formalism for electron beam reference dosimetry using updated Monte Carlo calculated beam quality conversion factors. METHODS The proposed, simplified formalism allows the use of cylindrical ionization chambers in all electron beams (even those with low beam energies) and does not require a measured gradient correction factor. Data from a previous publication are used for beam quality conversion factors. The formalism is tested and compared to the present formalism in the AAPM TG-51 protocol with measurements made in Elekta Precise electron beams with energies between 4 MeV and 22 MeV and with fields shaped with a 10 × 10 cm2 clinical applicator as well as a 20 × 20 cm2 clinical applicator for the 18 MeV and 22 MeV beams. A set of six ionization chambers are used for measurements (two cylindical reference-class chambers, two scanning-type chambers and two parallel-plate chambers). Dose per monitor unit is derived using the data and formalism provided in the TG-51 protocol and with the proposed formalism and data and compared to that obtained using ionization chambers calibrated directly against primary standards for absorbed dose in electron beams. RESULTS The standard deviation of results using different chambers when TG-51 is followed strictly is on the order of 0.4% when parallel-plate chambers are cross-calibrated against cylindrical chambers. However, if parallel-plate chambers are directly calibrated in a cobalt-60 beam, the difference between results for these chambers is up to 2.2%. Using the proposed formalism and either directly calibrated or cross-calibrated parallel-plate chambers gives a standard deviation using different chambers of 0.4%. The difference between results that use TG-51 and the primary standard measurements are on the order of 0.6% with a maximum difference in the 4 MeV beam of 2.8%. Comparing the results obtained with the proposed formalism and the primary standard measurements are on the order of 0.4% with a maximum difference of 1.0% in the 4 MeV beam. CONCLUSIONS The proposed formalism and the use of updated data for beam quality conversion factors improves the consistency of results obtained with different chamber types and improves the accuracy of reference dosimetry measurements. Moreover, it is simpler than the present formalism and will be straightforward to implement clinically.
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Affiliation(s)
- Bryan R Muir
- NRC Metrology Research Centre, National Research Council of Canada, Ottawa, ON, K1A 0R6, Canada
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Baumann K, Horst F, Zink K, Gomà C. Comparison of penh, fluka, and Geant4/topas for absorbed dose calculations in air cavities representing ionization chambers in high-energy photon and proton beams. Med Phys 2019; 46:4639-4653. [PMID: 31350915 PMCID: PMC6851981 DOI: 10.1002/mp.13737] [Citation(s) in RCA: 19] [Impact Index Per Article: 3.8] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/03/2018] [Revised: 07/01/2019] [Accepted: 07/16/2019] [Indexed: 12/16/2022] Open
Abstract
PURPOSE The purpose of this work is to analyze whether the Monte Carlo codes penh, fluka, and geant4/topas are suitable to calculate absorbed doses andf Q / f Q 0 ratios in therapeutic high-energy photon and proton beams. METHODS We used penh, fluka, geant4/topas, and egsnrc to calculate the absorbed dose to water in a reference water cavity and the absorbed dose to air in two air cavities representative of a plane-parallel and a cylindrical ionization chamber in a 1.25 MeV photon beam and a 150 MeV proton beam - egsnrc was only used for the photon beam calculations. The physics and transport settings in each code were adjusted to simulate the particle transport as detailed as reasonably possible. From these absorbed doses, f Q 0 factors, f Q factors, andf Q / f Q 0 ratios (which are the basis of Monte Carlo calculated beam quality correction factors k Q , Q 0 ) were calculated and compared between the codes. Additionally, we calculated the spectra of primary particles and secondary electrons in the reference water cavity, as well as the integrated depth-dose curve of 150 MeV protons in water. RESULTS The absorbed doses agreed within 1.4% or better between the individual codes for both the photon and proton simulations. The f Q 0 and f Q factors agreed within 0.5% or better for the individual codes for both beam qualities. The resultingf Q / f Q 0 ratios for 150 MeV protons agreed within 0.7% or better. For the 1.25 MeV photon beam, the spectra of photons and secondary electrons agreed almost perfectly. For the 150 MeV proton simulation, we observed differences in the spectra of secondary protons whereas the spectra of primary protons and low-energy delta electrons also agreed almost perfectly. The first 2 mm of the entrance channel of the 150 MeV proton Bragg curve agreed almost perfectly while for greater depths, the differences in the integrated dose were up to 1.5%. CONCLUSION penh, fluka, and geant4/topas are capable of calculating beam quality correction factors in proton beams. The differences in the f Q 0 and f Q factors between the codes are 0.5% at maximum. The differences in thef Q / f Q 0 ratios are 0.7% at maximum.
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Affiliation(s)
- Kilian‐Simon Baumann
- Department of Radiotherapy and RadiooncologyUniversity Medical Center Giessen‐MarburgMarburgGermany
- Institute of Medical Physics and Radiation ProtectionUniversity of Applied SciencesGiessenGermany
| | - Felix Horst
- Institute of Medical Physics and Radiation ProtectionUniversity of Applied SciencesGiessenGermany
- GSI Helmholtzzentrum für SchwerionenforschungDarmstadtGermany
| | - Klemens Zink
- Department of Radiotherapy and RadiooncologyUniversity Medical Center Giessen‐MarburgMarburgGermany
- Institute of Medical Physics and Radiation ProtectionUniversity of Applied SciencesGiessenGermany
- Frankfurt Institute for Advanced Studies (FIAS)FrankfurtGermany
| | - Carles Gomà
- Department of Oncology, Laboratory of Experimental RadiotherapyKU LeuvenLeuvenBelgium
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Hartmann GH, Zink K. A Monte Carlo study on the PTW 60019 microDiamond detector. Med Phys 2019; 46:5159-5172. [DOI: 10.1002/mp.13721] [Citation(s) in RCA: 9] [Impact Index Per Article: 1.8] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/12/2018] [Revised: 07/02/2019] [Accepted: 07/03/2019] [Indexed: 11/12/2022] Open
Affiliation(s)
| | - Klemens Zink
- Institute of Medical Physics and Radiation Protection (IMPS) University of Applied Sciences Giessen 35390Giessen Germany
- Department for Radiotherapy and Radiooncology University Medical Center Giessen‐Marburg 35043Marburg Germany
- Frankfurt Institute for Advanced Studies (FIAS), Goethe‐University 60438Frankfurt Germany
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Rahimi SA, Hashemi B, Mahdavi SR. Estimation of Dosimetric Parameters based on K NR and K NCSF Correction Factors for Small Field Radiation Therapy at 6 and 18 MV Linac Energies using Monte Carlo Simulation Methods. J Biomed Phys Eng 2019; 9:37-50. [PMID: 30881933 PMCID: PMC6409371] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/24/2015] [Accepted: 12/24/2016] [Indexed: 06/09/2023]
Abstract
BACKGROUND Estimating dosimetric parameters for small fields under non-reference conditions leads to significant errors if done based on conventional protocols used for large fields in reference conditions. Hence, further correction factors have been introduced to take into account the influence of spectral quality changes when various detectors are used in non-reference conditions at different depths and field sizes. OBJECTIVE Determining correction factors (KNR and KNCSF) recommended recently for small field dosimetry formalism by American Association of Physicists in Medicine (AAPM) for different detectors at 6 and 18 MV photon beams. METHODS EGSnrc Monte Carlo code was used to calculate the doses measured with different detectors located in a slab phantom and the recommended KNR and KNCSF correction factors for various circular small field sizes ranging from 5-30 mm diameters. KNR and KNCSF correction factors were determined for different active detectors (a pinpoint chamber, EDP-20 and EDP-10 diodes) in a homogeneous phantom irradiated to 6 and 18 MV photon beams of a Varian linac (2100C/D). RESULTS KNR correction factor estimated for the highest small circular field size of 30 mm diameter for the pinpoint chamber, EDP-20 and EDP-10 diodes were 0.993, 1.020 and 1.054; and 0.992, 1.054 and 1.005 for the 6 and 18 MV beams, respectively. The KNCSF correction factor estimated for the lowest circular field size of 5 mm for the pinpoint chamber, EDP-20 and EDP-10 diodes were 0.994, 1.023, and 1.040; and 1.000, 1.014, and 1.022 for the 6 and 18 MV photon beams, respectively. CONCLUSION Comparing the results obtained for the detectors used in this study reveals that the unshielded diodes (EDP-20 and EDP-10) can confidently be recommended for small field dosimetry as their correction factors (KNR and KNCSF) was close to 1.0 for all small field sizes investigated and are mainly independent from the electron beam spot size.
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Affiliation(s)
- S A Rahimi
- PhD Candidate, Department of Medical Physics, Faculty of Medical Sciences, Tarbiat Modares University, Tehran, Iran
- Assistant Professor, Department of Basic Sciences, Faculty of Health Sciences, Mazandaran University of Medical Sciences, Sari, Iran
| | - B Hashemi
- Associate Professor, Department of Medical Physics, Faculty of Medical Sciences, Tarbiat Modares University, Tehran, Iran
| | - S R Mahdavi
- Associate Professor, Department of Medical Physics, Faculty of Medicine, Iran University of Medical Sciences, Tehran, Iran
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Czarnecki D, Poppe B, Zink K. Impact of new ICRU Report 90 recommendations on calculated correction factors for reference dosimetry. Phys Med Biol 2018; 63:155015. [PMID: 29974869 DOI: 10.1088/1361-6560/aad148] [Citation(s) in RCA: 19] [Impact Index Per Article: 3.2] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/11/2022]
Abstract
In 2016 the ICRU published a new report dealing with key data for ionizing radiation dosimetry (ICRU Report 90). New recommendations have been made for the mean excitation energies I for air, graphite and liquid water as well as for the graphite density to use when evaluating the density effect. In addition, the ICRU Report 90 discusses renormalized photoelectric cross sections, but refuses to give a recommendation on the use of renormalization factors. However, the Consultative Committee for Ionizing Radiation recommends to use renormalized photoeffect cross sections. Goal of the present work is to evaluate the impact of these new recommendations on clinical reference dosimetry for high energy photon and electron beams. The beam quality correction factor k Q was calculated by Monte Carlo simulations for compact and parallel plate ionization chambers. In case of photons seven phase space files from clinical accelerators and twelve spectra taken from literature from 4 MV to 24 MV and additionally a 60Co source were applied. As electron source thirteen electron spectra available in literature were used in the range of 4 MeV-21 MeV. The new ICRU recommendations have a small impact on Monte Carlo calculated k Q values for the chosen ionization chambers in the range of 0.1%-0.35% only-the difference increases for higher photon energies. The impact of the ICRU Report 90 recommendations on Monte Carlo calculated stopping power ratios s w,a , perturbation factors p and beam quality correction factors k Q was investigated and confirmed a decrese of s w,a by a fraction of a percent for photon and electron beams. This study indicates that the impact of the new ICRU recommendation is within 0.35%. The determined deviations should be taken into account, when widely published Monte Carlo calculated values are examined.
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Affiliation(s)
- Damian Czarnecki
- Institute of Medical Physics and Radiation Protection, University of Applied Sciences Giessen, Giessen, Germany. University Clinic for Medical Radiation Physics, Medical Campus Pius Hospital, Carl von Ossietzky University, Oldenburg, Germany
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Wulff J, Baumann KS, Verbeek N, Bäumer C, Timmermann B, Zink K. TOPAS/Geant4 configuration for ionization chamber calculations in proton beams. ACTA ACUST UNITED AC 2018; 63:115013. [DOI: 10.1088/1361-6560/aac30e] [Citation(s) in RCA: 15] [Impact Index Per Article: 2.5] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/25/2022]
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Krauss A, Kapsch RP. Direct determination ofkQfactors for cylindrical and plane-parallel ionization chambers in high-energy electron beams from 6 MeV to 20 MeV. ACTA ACUST UNITED AC 2018; 63:035041. [DOI: 10.1088/1361-6560/aaa71e] [Citation(s) in RCA: 8] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/11/2022]
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17
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Muir BR, McEwen MR. Technical Note: On the use of cylindrical ionization chambers for electron beam reference dosimetry. Med Phys 2017; 44:6641-6646. [PMID: 28913919 DOI: 10.1002/mp.12582] [Citation(s) in RCA: 6] [Impact Index Per Article: 0.9] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/17/2017] [Revised: 07/26/2017] [Accepted: 08/31/2017] [Indexed: 11/07/2022] Open
Abstract
PURPOSE To investigate the use of cylindrical chambers for electron beam dosimetry independent of energy by studying the variability of relative ion chamber perturbation corrections, one of the main concerns for electron beam dosimetry with cylindrical chambers. METHODS Measurements are made with sets of cylindrical and plane-parallel reference-class chambers as a function of depth in water in 8 MeV and 18 MeV electron beams. The ratio of chamber readings for similar chambers is normalized in a high-energy electron beam and can be thought of as relative perturbation corrections. Data are plotted as a function of mean electron energy at depth for a range of depths close to the phantom surface to R80 , the depth at which the ionization falls to 80% of its maximum value. Additional, similar measurements are made in a Virtual Water® phantom with cylindrical chambers at the reference depth in a 4 MeV electron beam. RESULTS The variability of relative ion chamber perturbation corrections for nominally identical cylindrical Farmer-type chambers is found to be less than 0.4%, no worse than plane-parallel chambers with similar specifications. CONCLUSIONS This work discusses several issues related to the use of plane-parallel ion chambers and suggests that reference-class cylindrical chambers may be appropriate for reference dosimetry of all electron beams. This would simplify the reference dosimetry procedure and improve accuracy of beam calibration.
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Affiliation(s)
- Bryan R Muir
- Measurement Science and Standards, National Research Council of Canada, Ottawa, ON, K1A 0R6, Canada
| | - Malcolm R McEwen
- Measurement Science and Standards, National Research Council of Canada, Ottawa, ON, K1A 0R6, Canada
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Kulmala A, Tenhunen M. Ionization chamber radial response deconvolution in megavoltage photon beam. Phys Med Biol 2017; 62:7505-7519. [PMID: 28486216 DOI: 10.1088/1361-6560/aa71f7] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/11/2022]
Abstract
The aim of this paper is to study a radial response model as a method, to correct output factor results gathered with ionization chambers of different size and shape in cone collimated RT fields. An enhanced version of a non-parametric super-resolution deconvolution method able to model a radial response function of a small cylinder symmetric ionization chamber is described and demonstrated. The radial response of four ionization chambers with different geometry and radius are estimated using 6 MV photon beam in water at the isocentre plane. Finally the validity of the estimates is tested by applying the response functions to the output factor measurements of 4-20 mm conical collimators. The enhanced method is demonstrated by obtaining the response function characteristics with a spatial uncertainty smaller than 0.1 mm when the distance from chamber axis is larger than 0.5 mm. In all studied ionization chambers, a significant local response maximum is found close to the air cavity boundary. The agreement between the output factor results of different chambers is promising, the largest difference (max-min) in output factor is 4% obtained for the smallest 4 mm cone size.
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Affiliation(s)
- A Kulmala
- Helsinki University Hospital, Cancer Center, PO Box 180, 00029 Helsinki, Finland. Doctoral programme in Materials Research and Nanosciences (MATRENA), University of Helsinki, Finland
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19
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Muir BR, Cojocaru CD, McEwen MR, Ross CK. Electron beam water calorimetry measurements to obtain beam quality conversion factors. Med Phys 2017; 44:5433-5444. [DOI: 10.1002/mp.12463] [Citation(s) in RCA: 8] [Impact Index Per Article: 1.1] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/02/2017] [Revised: 06/20/2017] [Accepted: 07/02/2017] [Indexed: 11/06/2022] Open
Affiliation(s)
- Bryan R. Muir
- Measurement Science and Standards; National Research Council of Canada; Ottawa ON K1A 0R6 Canada
| | - Claudiu D. Cojocaru
- Measurement Science and Standards; National Research Council of Canada; Ottawa ON K1A 0R6 Canada
| | - Malcolm R. McEwen
- Measurement Science and Standards; National Research Council of Canada; Ottawa ON K1A 0R6 Canada
| | - Carl K. Ross
- Measurement Science and Standards; National Research Council of Canada; Ottawa ON K1A 0R6 Canada
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20
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Computation of the electron beam qualitykQ,Q0factors for the NE2571, NE2571A and NE2581A thimble ionization chambers using PENELOPE. Phys Med 2017; 38:76-80. [DOI: 10.1016/j.ejmp.2017.05.053] [Citation(s) in RCA: 3] [Impact Index Per Article: 0.4] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 03/18/2017] [Revised: 05/01/2017] [Accepted: 05/03/2017] [Indexed: 11/24/2022] Open
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21
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Fagerstrom JM, Bender ET, Lawless MJ, Culberson WS. Design of a modulated orthovoltage stereotactic radiosurgery system. Med Phys 2017; 44:3776-3787. [PMID: 28498612 DOI: 10.1002/mp.12336] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/06/2016] [Revised: 05/01/2017] [Accepted: 05/01/2017] [Indexed: 11/11/2022] Open
Abstract
PURPOSE To achieve stereotactic radiosurgery (SRS) dose distributions with sharp gradients using orthovoltage energy fluence modulation with inverse planning optimization techniques. METHODS A pencil beam model was used to calculate dose distributions from an orthovoltage unit at 250 kVp. Kernels for the model were derived using Monte Carlo methods. A Genetic Algorithm search heuristic was used to optimize the spatial distribution of added tungsten filtration to achieve dose distributions with sharp dose gradients. Optimizations were performed for depths of 2.5, 5.0, and 7.5 cm, with cone sizes of 5, 6, 8, and 10 mm. In addition to the beam profiles, 4π isocentric irradiation geometries were modeled to examine dose at 0.07 mm depth, a representative skin depth, for the low energy beams. Profiles from 4π irradiations of a constant target volume, assuming maximally conformal coverage, were compared. Finally, dose deposition in bone compared to tissue in this energy range was examined. RESULTS Based on the results of the optimization, circularly symmetric tungsten filters were designed to modulate the orthovoltage beam across the apertures of SRS cone collimators. For each depth and cone size combination examined, the beam flatness and 80-20% and 90-10% penumbrae were calculated for both standard, open cone-collimated beams as well as for optimized, filtered beams. For all configurations tested, the modulated beam profiles had decreased penumbra widths and flatness statistics at depth. Profiles for the optimized, filtered orthovoltage beams also offered decreases in these metrics compared to measured linear accelerator cone-based SRS profiles. The dose at 0.07 mm depth in the 4π isocentric irradiation geometries was higher for the modulated beams compared to unmodulated beams; however, the modulated dose at 0.07 mm depth remained <0.025% of the central, maximum dose. The 4π profiles irradiating a constant target volume showed improved statistics for the modulated, filtered distribution compared to the standard, open cone-collimated distribution. Simulations of tissue and bone confirmed previously published results that a higher energy beam (≥ 200 keV) would be preferable, but the 250 kVp beam was chosen for this work because it is available for future measurements. CONCLUSIONS A methodology has been described that may be used to optimize the spatial distribution of added filtration material in an orthovoltage SRS beam to result in dose distributions with decreased flatness and penumbra statistics compared to standard open cones. This work provides the mathematical foundation for a novel, orthovoltage energy fluence-modulated SRS system.
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Affiliation(s)
- Jessica M Fagerstrom
- Department of Medical Physics, School of Medicine and Public Health, University of Wisconsin-Madison, Madison, WI, 53705, USA
| | | | - Michael J Lawless
- Department of Human Oncology, School of Medicine and Public Health, University of Wisconsin-Madison, Madison, WI, 53705, USA
| | - Wesley S Culberson
- Department of Medical Physics, School of Medicine and Public Health, University of Wisconsin-Madison, Madison, WI, 53705, USA
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22
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Scalchi P, Ciccotelli A, Felici G, Petrucci A, Massafra R, Piazzi V, D'Avenia P, Cavagnetto F, Cattani F, Romagnoli R, Soriani A. Use of parallel-plate ionization chambers in reference dosimetry of NOVAC and LIAC®mobile electron linear accelerators for intraoperative radiotherapy: a multi-center survey. Med Phys 2017; 44:321-332. [DOI: 10.1002/mp.12020] [Citation(s) in RCA: 15] [Impact Index Per Article: 2.1] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/15/2016] [Revised: 11/06/2016] [Accepted: 11/11/2016] [Indexed: 11/12/2022] Open
Affiliation(s)
- Paolo Scalchi
- Department of Medical Physics; Azienda U.L.S.S. 8; Vicenza 36100 Italy
| | | | | | - Assunta Petrucci
- Department of Medical Physics; S. Filippo Neri Hospital; Rome 00135 Italy
| | - Raffaella Massafra
- Department of Medical Physics; I.R.C.C.S. Institute of Oncology Giovanni Paolo II; Bari 70124 Italy
| | - Valeria Piazzi
- Department of Radiotherapy; Multimedica Hospital; Castellanza 21053 Italy
| | - Paola D'Avenia
- Department of Medical Physics; ASUR MARCHE AV3; Macerata 62100 Italy
| | | | - Federica Cattani
- Department of Medical Physics; European Institute of Oncology; Milan 20141 Italy
| | | | - Antonella Soriani
- Laboratory of Medical Physics and Expert Systems; Regina Elena National Cancer Institute; Rome 00144 Italy
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23
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Gomà C, Andreo P, Sempau J. Monte Carlo calculation of beam quality correction factors in proton beams using detailed simulation of ionization chambers. Phys Med Biol 2016; 61:2389-406. [DOI: 10.1088/0031-9155/61/6/2389] [Citation(s) in RCA: 35] [Impact Index Per Article: 4.4] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/11/2022]
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24
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Reis C, Nicolucci P. Assessment of ionization chamber correction factors in photon beams using a time saving strategy with PENELOPE code. Phys Med 2016; 32:297-304. [DOI: 10.1016/j.ejmp.2016.01.482] [Citation(s) in RCA: 4] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 10/07/2015] [Revised: 01/20/2016] [Accepted: 01/22/2016] [Indexed: 10/22/2022] Open
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[Benchmark experiment to verify radiation transport calculations for dosimetry in radiation therapy]. Z Med Phys 2015; 26:209-23. [PMID: 26422577 DOI: 10.1016/j.zemedi.2015.06.009] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.2] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/03/2015] [Revised: 06/08/2015] [Accepted: 06/12/2015] [Indexed: 11/22/2022]
Abstract
Monte Carlo simulations are regarded as the most accurate method of solving complex problems in the field of dosimetry and radiation transport. In (external) radiation therapy they are increasingly used for the calculation of dose distributions during treatment planning. In comparison to other algorithms for the calculation of dose distributions, Monte Carlo methods have the capability of improving the accuracy of dose calculations - especially under complex circumstances (e.g. consideration of inhomogeneities). However, there is a lack of knowledge of how accurate the results of Monte Carlo calculations are on an absolute basis. A practical verification of the calculations can be performed by direct comparison with the results of a benchmark experiment. This work presents such a benchmark experiment and compares its results (with detailed consideration of measurement uncertainty) with the results of Monte Carlo calculations using the well-established Monte Carlo code EGSnrc. The experiment was designed to have parallels to external beam radiation therapy with respect to the type and energy of the radiation, the materials used and the kind of dose measurement. Because the properties of the beam have to be well known in order to compare the results of the experiment and the simulation on an absolute basis, the benchmark experiment was performed using the research electron accelerator of the Physikalisch-Technische Bundesanstalt (PTB), whose beam was accurately characterized in advance. The benchmark experiment and the corresponding Monte Carlo simulations were carried out for two different types of ionization chambers and the results were compared. Considering the uncertainty, which is about 0.7 % for the experimental values and about 1.0 % for the Monte Carlo simulation, the results of the simulation and the experiment coincide.
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26
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Bailey M, Shipley DR, Manning JW. Roos and NACP-02 ion chamber perturbations and water-air stopping-power ratios for clinical electron beams for energies from 4 to 22 MeV. Phys Med Biol 2015; 60:1087-105. [PMID: 25586026 DOI: 10.1088/0031-9155/60/3/1087] [Citation(s) in RCA: 5] [Impact Index Per Article: 0.6] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/12/2022]
Abstract
Empirical fits are developed for depth-compensated wall- and cavity-replacement perturbations in the PTW Roos 34001 and IBA / Scanditronix NACP-02 parallel-plate ionisation chambers, for electron beam qualities from 4 to 22 MeV for depths up to approximately 1.1 × R₅₀,D. These are based on calculations using the Monte Carlo radiation transport code EGSnrc and its user codes with a full simulation of the linac treatment head modelled using BEAMnrc. These fits are used with calculated restricted stopping-power ratios between air and water to match measured depth-dose distributions in water from an Elekta Synergy clinical linear accelerator at the UK National Physical Laboratory. Results compare well with those from recent publications and from the IPEM 2003 electron beam radiotherapy Code of Practice.
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Affiliation(s)
- M Bailey
- Radiation Dosimetry, National Physical Laboratory, Hampton Road, Teddington, Middlesex, TW11 0LW, UK
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27
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Zink K, Czarnecki D, Looe HK, von Voigts-Rhetz P, Harder D. Monte Carlo study of the depth-dependent fluence perturbation in parallel-plate ionization chambers in electron beams. Med Phys 2014; 41:111707. [PMID: 25370621 DOI: 10.1118/1.4897389] [Citation(s) in RCA: 6] [Impact Index Per Article: 0.6] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/07/2022] Open
Abstract
PURPOSE The electron fluence inside a parallel-plate ionization chamber positioned in a water phantom and exposed to a clinical electron beam deviates from the unperturbed fluence in water in absence of the chamber. One reason for the fluence perturbation is the well-known "inscattering effect," whose physical cause is the lack of electron scattering in the gas-filled cavity. Correction factors determined to correct for this effect have long been recommended. However, more recent Monte Carlo calculations have led to some doubt about the range of validity of these corrections. Therefore, the aim of the present study is to reanalyze the development of the fluence perturbation with depth and to review the function of the guard rings. METHODS Spatially resolved Monte Carlo simulations of the dose profiles within gas-filled cavities with various radii in clinical electron beams have been performed in order to determine the radial variation of the fluence perturbation in a coin-shaped cavity, to study the influences of the radius of the collecting electrode and of the width of the guard ring upon the indicated value of the ionization chamber formed by the cavity, and to investigate the development of the perturbation as a function of the depth in an electron-irradiated phantom. The simulations were performed for a primary electron energy of 6 MeV. RESULTS The Monte Carlo simulations clearly demonstrated a surprisingly large in- and outward electron transport across the lateral cavity boundary. This results in a strong influence of the depth-dependent development of the electron field in the surrounding medium upon the chamber reading. In the buildup region of the depth-dose curve, the in-out balance of the electron fluence is positive and shows the well-known dose oscillation near the cavity/water boundary. At the depth of the dose maximum the in-out balance is equilibrated, and in the falling part of the depth-dose curve it is negative, as shown here the first time. The influences of both the collecting electrode radius and the width of the guard ring are reflecting the deep radial penetration of the electron transport processes into the gas-filled cavities and the need for appropriate corrections of the chamber reading. New values for these corrections have been established in two forms, one converting the indicated value into the absorbed dose to water in the front plane of the chamber, the other converting it into the absorbed dose to water at the depth of the effective point of measurement of the chamber. In the Appendix, the in-out imbalance of electron transport across the lateral cavity boundary is demonstrated in the approximation of classical small-angle multiple scattering theory. CONCLUSIONS The in-out electron transport imbalance at the lateral boundaries of parallel-plate chambers in electron beams has been studied with Monte Carlo simulation over a range of depth in water, and new correction factors, covering all depths and implementing the effective point of measurement concept, have been developed.
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Affiliation(s)
- K Zink
- Institute of Medical Physics and Radiation Protection (IMPS), University of Applied Sciences Giessen, Giessen D-35390, Germany and Department of Radiotherapy and Radiooncology, University Medical Center Giessen-Marburg, Marburg D-35043, Germany
| | - D Czarnecki
- Institute of Medical Physics and Radiation Protection (IMPS), University of Applied Sciences Giessen, Giessen D-35390, Germany
| | - H K Looe
- Clinic for Radiation Therapy, Pius-Hospital, Oldenburg D-26129, Germany and WG Medical Radiation Physics, Carl von Ossietzky University, Oldenburg D-26129, Germany
| | - P von Voigts-Rhetz
- Institute of Medical Physics and Radiation Protection (IMPS), University of Applied Sciences Giessen, Giessen D-35390, Germany
| | - D Harder
- Prof. em., Medical Physics and Biophysics, Georg August University, Göttingen D-37073, Germany
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Erazo F, Brualla L, Lallena AM. Electron beam qualitykQ,Q0factors for various ionization chambers: a Monte Carlo investigation with penelope. Phys Med Biol 2014; 59:6673-91. [DOI: 10.1088/0022-3727/59/21/6673] [Citation(s) in RCA: 7] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/11/2022]
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29
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Muir BR, Rogers DWO. Monte Carlo calculations of electron beam quality conversion factors for several ion chamber types. Med Phys 2014; 41:111701. [DOI: 10.1118/1.4893915] [Citation(s) in RCA: 25] [Impact Index Per Article: 2.5] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/07/2023] Open
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30
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Muir BR, McEwen MR, Rogers DWO. Determination of relative ion chamber calibration coefficients from depth-ionization measurements in clinical electron beams. Phys Med Biol 2014; 59:5953-69. [PMID: 25211012 DOI: 10.1088/0031-9155/59/19/5953] [Citation(s) in RCA: 7] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/11/2022]
Abstract
A method is presented to obtain ion chamber calibration coefficients relative to secondary standard reference chambers in electron beams using depth-ionization measurements. Results are obtained as a function of depth and average electron energy at depth in 4, 8, 12 and 18 MeV electron beams from the NRC Elekta Precise linac. The PTW Roos, Scanditronix NACP-02, PTW Advanced Markus and NE 2571 ion chambers are investigated. The challenges and limitations of the method are discussed. The proposed method produces useful data at shallow depths. At depths past the reference depth, small shifts in positioning or drifts in the incident beam energy affect the results, thereby providing a built-in test of incident electron energy drifts and/or chamber set-up. Polarity corrections for ion chambers as a function of average electron energy at depth agree with literature data. The proposed method produces results consistent with those obtained using the conventional calibration procedure while gaining much more information about the behavior of the ion chamber with similar data acquisition time. Measurement uncertainties in calibration coefficients obtained with this method are estimated to be less than 0.5%. These results open up the possibility of using depth-ionization measurements to yield chamber ratios which may be suitable for primary standards-level dissemination.
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Affiliation(s)
- B R Muir
- Measurement Science and Standards, National Research Council of Canada, Ottawa, ON, K1A 0R6, Canada
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31
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von Voigts-Rhetz P, Czarnecki D, Zink K. Effective point of measurement for parallel plate and cylindrical ion chambers in megavoltage electron beams. Z Med Phys 2014; 24:216-23. [PMID: 24418322 DOI: 10.1016/j.zemedi.2013.12.001] [Citation(s) in RCA: 5] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/31/2013] [Revised: 12/02/2013] [Accepted: 12/02/2013] [Indexed: 10/25/2022]
Abstract
The presence of an air filled ionization chamber in a surrounding medium introduces several fluence perturbations in high energy photon and electron beams which have to be accounted for. One of these perturbations, the displacement effect, may be corrected in two different ways: by a correction factor pdis or by the application of the concept of the effective point of measurement (EPOM). The latter means, that the volume averaged ionization within the chamber is not reported to the chambers reference point but to a point within the air filled cavity. Within this study the EPOM was determined for four different parallel plate and two cylindrical chambers in megavoltage electron beams using Monte Carlo simulations. The positioning of the chambers with this EPOM at the depth of measurement results in a largely depth independent residual perturbation correction, which is determined within this study for the first time. For the parallel plate chambers the EPOM is independent of the energy of the primary electrons. Whereas for the Advanced Markus chamber the position of the EPOM coincides with the chambers reference point, it is shifted for the other parallel plate chambers several tenths of millimeters downstream the beam direction into the air filled cavity. For the cylindrical chambers there is an increasing shift of the EPOM with increasing electron energy. This shift is in upstream direction, i.e. away from the chambers reference point toward the focus. For the highest electron energy the position of the calculated EPOM is in fairly good agreement with the recommendation given in common dosimetry protocols, for the smallest energy, the calculated EPOM positions deviate about 30% from this recommendation.
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Affiliation(s)
- Philip von Voigts-Rhetz
- Institut für Medizinische Physik und Strahlenschutz - IMPS, Technische Hochschule Mittelhessen, University of Applied Sciences, Gießen, Germany.
| | - Damian Czarnecki
- Institut für Medizinische Physik und Strahlenschutz - IMPS, Technische Hochschule Mittelhessen, University of Applied Sciences, Gießen, Germany
| | - Klemens Zink
- Institut für Medizinische Physik und Strahlenschutz - IMPS, Technische Hochschule Mittelhessen, University of Applied Sciences, Gießen, Germany; University Hospital Marburg, Department of Radiotherapy and Radiation Oncology, Philipps-University, Marburg, Germany
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32
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Muir BR, Rogers DWO. Monte Carlo calculations for reference dosimetry of electron beams with the PTW Roos and NE2571 ion chambers. Med Phys 2013; 40:121722. [DOI: 10.1118/1.4829577] [Citation(s) in RCA: 17] [Impact Index Per Article: 1.5] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/15/2022] Open
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