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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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Oguchi H. [5. Standard Dosimetry of Absorbed Dose to Water in External Beam Radiotherapy for Electron Beams -Focusing on Appendix]. Nihon Hoshasen Gijutsu Gakkai Zasshi 2024; 80:104-111. [PMID: 38246632 DOI: 10.6009/jjrt.2024-2301] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/23/2024]
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Yasui K, Nakajima Y, Suda Y, Arai Y, Takizawa T, Sakai K, Fujita Y. Experimental investigation of the effective point of measurement for plane-parallel chambers used in electron beam dosimetry. J Appl Clin Med Phys 2023:e14059. [PMID: 37307247 DOI: 10.1002/acm2.14059] [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: 12/08/2022] [Revised: 03/07/2023] [Accepted: 05/18/2023] [Indexed: 06/14/2023] Open
Abstract
In this study, the effective point of measurement (EPOM) for plane-parallel ionization chambers in clinical high-energy electron beams was determined experimentally. Previous studies have reported that the EPOM of plane-parallel chambers is shifted several tens of millimeters downstream from the inner surface of the entrance window to the cavity. These findings were based on the Monte Carlo (MC) simulation, and few experimental studies have been performed. Thus, additional experimental validations of the reported EPOMs were required. In this study, we investigated the EPOMs of three plane-parallel chambers (NACP-02, Roos and Advanced Markus) for clinical electron beams. The EPOMs were determined by comparing the measured percentage depth-dose (PDD) of the plane-parallel chambers and the PDD obtained using the microDiamond detector. The optimal shift to the EPOM was energy-dependent. The determined EPOM showed no chamber-to-chamber variation, thereby allowing the use of a single value. The mean optimal shifts were 0.104 ± 0.011, 0.040 ± 0.012, and 0.012 ± 0.009 cm for NACP-02, Roos, and Advanced Markus, respectively. These values are valid in the R50 range from 2.40 to 8.82 cm, which correspond to 6-22 MeV. Roos and Advanced Markus exhibited similar results to those of the previous studies, but NACP-02 showed a larger shift. This is probably due to the uncertainty of the entrance window of NACP-02. Therefore, it is necessary to carefully consider where the optimal EPOM is located when using this chamber.
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Affiliation(s)
- Kohki Yasui
- Department of Radiological Sciences, Komazawa University Graduate School, Setagaya-ku, Tokyo, Japan
- Department of Radiation Oncology, Tokyo Metropolitan Cancer and Infectious Diseases Center Komagome Hospital, Bunkyo-ku, Tokyo, Japan
| | - Yujiro Nakajima
- Department of Radiation Oncology, Tokyo Metropolitan Cancer and Infectious Diseases Center Komagome Hospital, Bunkyo-ku, Tokyo, Japan
- Department of Radiological Sciences, Komazawa University, Setagaya-ku, Tokyo, Japan
| | - Yuhi Suda
- Department of Radiation Oncology, Tokyo Metropolitan Cancer and Infectious Diseases Center Komagome Hospital, Bunkyo-ku, Tokyo, Japan
| | - Yu Arai
- Department of Radiation Oncology, Tokyo Metropolitan Cancer and Infectious Diseases Center Komagome Hospital, Bunkyo-ku, Tokyo, Japan
| | - Takuto Takizawa
- Department of Radiation Oncology, Tokyo Metropolitan Cancer and Infectious Diseases Center Komagome Hospital, Bunkyo-ku, Tokyo, Japan
| | - Kaito Sakai
- Department of Radiological Sciences, Komazawa University Graduate School, Setagaya-ku, Tokyo, Japan
- Department of Radiation Oncology, Tokyo Metropolitan Cancer and Infectious Diseases Center Komagome Hospital, Bunkyo-ku, Tokyo, Japan
| | - Yukio Fujita
- Department of Radiological Sciences, Komazawa University, Setagaya-ku, Tokyo, Japan
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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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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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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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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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Renaud J, Sarfehnia A, Marchant K, McEwen M, Ross C, Seuntjens J. Direct measurement of electron beam quality conversion factors using water calorimetry. Med Phys 2015; 42:6357-68. [DOI: 10.1118/1.4931970] [Citation(s) in RCA: 13] [Impact Index Per Article: 1.4] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/07/2022] Open
Affiliation(s)
- James Renaud
- Medical Physics Unit, McGill University, Montréal, Québec H3G 1A4, Canada
| | - Arman Sarfehnia
- Medical Physics Unit, McGill University, Montréal, Québec H3G 1A4, Canada and Department of Radiation Oncology, University of Toronto, Toronto, Ontario M5S 3E2, Canada
| | - Kristin Marchant
- Allan Blair Cancer Centre, Saskatchewan Cancer Agency, Regina, Saskatchewan S4T 7T1, Canada and Department of Oncology, University of Saskatchewan, Saskatoon, Saskatchewan S7N 5A1, Canada
| | - Malcolm McEwen
- Ionizing Radiation Standards, National Research Council of Canada, Ottawa, Ontario K1A 0R6, Canada
| | - Carl Ross
- Ionizing Radiation Standards, National Research Council of Canada, Ottawa, Ontario K1A 0R6, Canada
| | - Jan Seuntjens
- Medical Physics Unit, McGill University, Montréal, Québec H3G 1A4, Canada
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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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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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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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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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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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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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Araki F. Monte Carlo calculations of the replacement correction factor, P repl, for cylindrical chamber cavities in clinical photon and electron beams. Radiol Phys Technol 2012; 5:199-206. [DOI: 10.1007/s12194-012-0154-5] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/09/2011] [Revised: 04/07/2012] [Accepted: 04/11/2012] [Indexed: 10/28/2022]
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Zink K, Wulff J. Beam quality corrections for parallel-plate ion chambers in electron reference dosimetry. Phys Med Biol 2012; 57:1831-54. [DOI: 10.1088/0031-9155/57/7/1831] [Citation(s) in RCA: 30] [Impact Index Per Article: 2.5] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/11/2022]
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Muir BR, McEwen MR, Rogers DWO. Beam quality conversion factors for parallel-plate ionization chambers in MV photon beams. Med Phys 2012; 39:1618-31. [DOI: 10.1118/1.3687864] [Citation(s) in RCA: 34] [Impact Index Per Article: 2.8] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/07/2022] Open
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Lacroix F, Guillot M, McEwen M, Gingras L, Beaulieu L. Extraction of depth-dependent perturbation factors for silicon diodes using a plastic scintillation detector. Med Phys 2011; 38:5441-7. [DOI: 10.1118/1.3637496] [Citation(s) in RCA: 7] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/07/2022] Open
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Ono T, Araki F, Yoshiyama F. Possibility of using cylindrical ionization chambers for percent depth-dose measurements in clinical electron beams. Med Phys 2011; 38:4647-54. [DOI: 10.1118/1.3608903] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/07/2022] Open
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Zink K, Wulff J. On the wall perturbation correction for a parallel-plate NACP-02 chamber in clinical electron beams. Med Phys 2011; 38:1045-54. [PMID: 21452742 DOI: 10.1118/1.3544660] [Citation(s) in RCA: 14] [Impact Index Per Article: 1.1] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/07/2022] Open
Abstract
PURPOSE In recent years, several Monte Carlo studies have been published concerning the perturbation corrections of a parallel-plate chamber in clinical electron beams. In these studies, a strong depth dependence of the relevant correction factors (p(wall) and P(cav)) for depth beyond the reference depth is recognized and it has been shown that the variation with depth is sensitive to the choice of the chamber's effective point of measurement. Recommendations concerning the positioning of parallel-plate ionization chambers in clinical electron beams are not the same for all current dosimetry protocols. The IAEA TRS-398 as well as the IPEM protocol and the German protocol DIN 6800-2 interpret the depth of measurement within the phantom as the water equivalent depth, i.e., the nonwater equivalence of the entrance window has to be accounted for by shifting the chamber by an amount deltaz. This positioning should ensure that the primary electrons traveling from the surface of the water phantom through the entrance window to the chamber's reference point sustain the same energy loss as the primary electrons in the undisturbed phantom. The objective of the present study is the determination of the shift deltaz for a NACP-02 chamber and the calculation of the resulting wall perturbation correction as a function of depth. Moreover, the contributions of the different chamber walls to the wall perturbation correction are identified. METHODS The dose and fluence within the NACP-02 chamber and a wall-less air cavity is calculated using the Monte Carlo code EGSnrc in a water phantom at different depths for different clinical electron beams. In order to determine the necessary shift to account for the nonwater equivalence of the entrance window, the chamber is shifted in steps deltaz around the depth of measurement. The optimal shift deltaz is determined from a comparison of the spectral fluence within the chamber and the bare cavity. The wall perturbation correction is calculated as the ratio between doses for the complete chamber and a wall-less air cavity. RESULTS The high energy part of the fluence spectra within the chamber strongly varies even with small chamber shifts, allowing the determination of deltaz within micrometers. For the NACP-02 chamber a shift deltaz = -0.058 cm results. This value is independent of the energy of the primary electrons as well as of the depth within the phantom and it is in good agreement with the value recommended in the German dosimetry protocol. Applying this shift, the calculated wall perturbation correction as a function of depth is varying less than 1% from zero up to the half value depth R50 for electron energies in the range of 6-21 MeV. The remaining depth dependence can mainly be attributed to the scatter properties of the entrance window. When neglecting the nonwater equivalence of the entrance window, the variation of p(wall) with depth is up to 10% and more, especially for low electron energies. CONCLUSIONS The variation of the wall perturbation correction for the NACP-02 chamber in clinical electron beams strongly depends on the positioning of the chamber. Applying a shift deltaz = -0.058 cm toward the focus ensures that the primary electron spectrum within the chamber bears the largest resemblance to the fluence of a wall-less cavity. Hence, the influence of the chamber walls on the perturbation correction can be separated out and the residual variation of p(wall) with depth is minimized.
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Affiliation(s)
- K Zink
- University Hospital Marburg, Philipps-University, D-35043 Marburg, Germany
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Sharma PK, Jamema SV, Kaushik K, Budrukkar A, Jalali R, Deshpande DD, Tambe CM, Sarin R, Munshi A. Electron arc therapy for bilateral chest wall irradiation: treatment planning and dosimetric study. Clin Oncol (R Coll Radiol) 2010; 23:216-22. [PMID: 21185700 DOI: 10.1016/j.clon.2010.09.005] [Citation(s) in RCA: 7] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/09/2009] [Revised: 07/13/2010] [Accepted: 09/10/2010] [Indexed: 10/18/2022]
Abstract
AIMS The treatment of patients with synchronous bilateral breast cancer is a challenge. We present a report of dosimetric data of patients with bilateral chest walls as the target treated with electron arc therapy. MATERIALS AND METHODS Ten consecutive patients who had undergone electron arc therapy to the bilateral chest wall for breast cancer were analysed. After positioning and immobilisation, patients underwent computed tomography scans from the neck to the upper abdomen. Electron arc plans were generated using the PLATO RTS (V1.8.2 Nucletron) treatment planning system. Electron energy was chosen depending upon the depth and thickness of the planning target volume (PTV). For all patients, the arc angle ranged between 80 and 280° (start angle 80°, stop angle 280°). The homogeneity index, coverage index and doses to organs at risk were evaluated. The patient-specific output factor and thermoluminescence dosimetry (TLD) measurements were carried out for all patients. The total planned dose to the PTV was 50Gy/25 fractions/5 weeks. RESULTS The mean PTV (± standard deviation) was 568.9 (±116)cm(3). The mean PTV coverage was 89 (±5.8)% of the prescribed dose. For the right lung, the mean values of D(1) and D(10) were 46 (±7.6) and 30 (±9)Gy, respectively. For the left lung, the mean values of D(1) and D(10) were 45 (±7) and 27 (±8)Gy, respectively. For the heart, the mean values of D(1), D(5) and D(10) were 21 (±15), 13.5 (±12) and 9 (±9)Gy, respectively. The mean values of TLD at various pre-specified locations on the chest wall surface were 1.84, 1.82, 1.82, 1.89 and 1.78Gy, respectively CONCLUSION The electron arc technique for treating the bilateral chest wall is a feasible and pragmatic technique. This technique has the twin advantages of adequate coverage of the target volume and sparing of adjacent normal structures. However, compared with other techniques, it needs a firm quality assurance protocol for dosimetry and treatment delivery.
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Affiliation(s)
- P K Sharma
- Department of Medical Physics & Radiation Safety, International Oncology Centre, Fortis Hospital, Noida, India
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Lacroix F, Guillot M, McEwen M, Cojocaru C, Gingras L, Beddar AS, Beaulieu L. Extraction of depth-dependent perturbation factors for parallel-plate chambers in electron beams using a plastic scintillation detector. Med Phys 2010; 37:4331-42. [PMID: 20879593 DOI: 10.1118/1.3463383] [Citation(s) in RCA: 32] [Impact Index Per Article: 2.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/07/2022] Open
Abstract
PURPOSE This work presents the experimental extraction of the overall perturbation factor PQ in megavoltage electron beams for NACP-02 and Roos parallel-plate ionization chambers using a plastic scintillation detector (PSD). METHODS The authors used a single scanning PSD mounted on a high-precision scanning tank to measure depth-dose curves in 6, 12, and 18 MeV clinical electron beams. The authors also measured depth-dose curves using the NACP-02 and PTW Roos chambers. RESULTS The authors found that the perturbation factors for the NACP-02 and Roos chambers increased substantially with depth, especially for low-energy electron beams. The experimental results were in good agreement with the results of Monte Carlo simulations reported by other investigators. The authors also found that using an effective point of measurement (EPOM) placed inside the air cavity reduced the variation of perturbation factors with depth and that the optimal EPOM appears to be energy dependent. CONCLUSIONS A PSD can be used to experimentally extract perturbation factors for ionization chambers. The dosimetry protocol recommendations indicating that the point of measurement be placed on the inside face of the front window appear to be incorrect for parallel-plate chambers and result in errors in the R50 of approximately 0.4 mm at 6 MeV, 1.0 mm at 12 MeV, and 1.2 mm at 18 MeV.
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Affiliation(s)
- Frédéric Lacroix
- Département de Radio-Oncologie, Centre hospitalier de l'Université de Montréal, Québec, Canada.
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Wang LLW, Rogers DWO. Replacement correction factors for plane-parallel ion chambers in electron beams. Med Phys 2010; 37:461-5. [PMID: 20229854 DOI: 10.1118/1.3276735] [Citation(s) in RCA: 10] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/07/2022] Open
Abstract
PURPOSE Plane-parallel chambers are recommended by dosimetry protocols for measurements in (especially low-energy) electron beams. In dosimetry protocols, the replacement correction factor P(repl) is assumed unity for "well-guarded" plane-parallel chambers in electron beams when the front face of the cavity is the effective point of measurement. There is experimental evidence that ion chambers which are not well-guarded (e.g., Markus) have nonunity P(repl) values. Monte Carlo simulations are employed in this study to investigate the replacement correction factors for plane-parallel chambers in electron beams. METHODS Using previously established Monte Carlo calculation methods, the values of P(repl) are calculated with high statistical precision for the cavities of a variety of plane-parallel chambers in a water phantom irradiated by various electron beams. The dependences of the values of P(repl) on the beam quality, phantom depth, as well as the guard ring width are studied. RESULTS In the dose fall-off region for low-energy beams, the P(repl) values are very sensitive to depth. It is found that this is mainly due to the gradient effect, which originates from the fact that the effective point of measurement for many plane-parallel chambers should not be at the front face of the cavity but rather shifted toward the center of the cavity by a fraction of a millimeter. Using the front face of the cavity as the effective point of measurement, the calculated values of P(repl) at d(ref) are not unity for some well-guarded plane-parallel chambers. The calculated P(repl) values for the Roos chamber are close to 1 for all electron beams. The calculation results for the Markus chamber are in good agreement with the measured values. CONCLUSIONS The appropriate selection of the effective point of measurement for plane-parallel chambers in electron beams is an important issue. If the effective point of measurement is correctly accounted for, the P(repl) values would be almost independent of depth. Both the guard ring width and the ratio of the collecting volume diameter to the cavity thickness can influence the values of P(repl) For a diameter to thickness ratio of 5 (e.g., NACP02 chamber), the guard width has to be 6 mm for the chamber to be considered as well-guarded, i.e., have a P(repl) value of 1.00.
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Affiliation(s)
- Lilie L W Wang
- Ottawa Carleton Institute of Physics, Carleton University, Ottawa, Ontario K1S 5B6, Canada.
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Selvam TP, Bhola S. Technical Note: EGSnrc-based dosimetric study of the BEBIG C60o HDR brachytherapy sources. Med Phys 2010; 37:1365-70. [DOI: 10.1118/1.3326948] [Citation(s) in RCA: 22] [Impact Index Per Article: 1.6] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/07/2022] Open
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Gerig LH, Niedbala M, Nyiri BJ. Dose perturbations by two carbon fiber treatment couches and the ability of a commercial treatment planning system to predict these effects. Med Phys 2009; 37:322-8. [DOI: 10.1118/1.3271364] [Citation(s) in RCA: 32] [Impact Index Per Article: 2.1] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/07/2022] Open
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26
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Wang LLW, Rogers DWO. Replacement correction factors for cylindrical ion chambers in electron beams. Med Phys 2009; 36:4600-8. [DOI: 10.1118/1.3213094] [Citation(s) in RCA: 14] [Impact Index Per Article: 0.9] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/07/2022] Open
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Gerbi BJ, Antolak JA, Deibel FC, Followill DS, Herman MG, Higgins PD, Huq MS, Mihailidis DN, Yorke ED, Hogstrom KR, Khan FM. Recommendations for clinical electron beam dosimetry: supplement to the recommendations of Task Group 25. Med Phys 2009; 36:3239-79. [PMID: 19673223 DOI: 10.1118/1.3125820] [Citation(s) in RCA: 101] [Impact Index Per Article: 6.7] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/07/2022] Open
Abstract
The goal of Task Group 25 (TG-25) of the Radiation Therapy Committee of the American Association of.Physicists in Medicine (AAPM) was to provide a methodology and set of procedures for a medical physicist performing clinical electron beam dosimetry in the nominal energy range of 5-25 MeV. Specifically, the task group recommended procedures for acquiring basic information required for acceptance testing and treatment planning of new accelerators with therapeutic electron beams. Since the publication of the TG-25 report, significant advances have taken place in the field of electron beam dosimetry, the most significant being that primary standards laboratories around the world have shifted from calibration standards based on exposure or air kerma to standards based on absorbed dose to water. The AAPM has published a new calibration protocol, TG-51, for the calibration of high-energy photon and electron beams. The formalism and dosimetry procedures recommended in this protocol are based on the absorbed dose to water calibration coefficient of an ionization chamber at 60Co energy, N60Co(D,w), together with the theoretical beam quality conversion coefficient k(Q) for the determination of absorbed dose to water in high-energy photon and electron beams. Task Group 70 was charged to reassess and update the recommendations in TG-25 to bring them into alignment with report TG-51 and to recommend new methodologies and procedures that would allow the practicing medical physicist to initiate and continue a high quality program in clinical electron beam dosimetry. This TG-70 report is a supplement to the TG-25 report and enhances the TG-25 report by including new topics and topics that were not covered in depth in the TG-25 report. These topics include procedures for obtaining data to commission a treatment planning computer, determining dose in irregularly shaped electron fields, and commissioning of sophisticated special procedures using high-energy electron beams. The use of radiochromic film for electrons is addressed, and radiographic film that is no longer available has been replaced by film that is available. Realistic stopping-power data are incorporated when appropriate along with enhanced tables of electron fluence data. A larger list of clinical applications of electron beams is included in the full TG-70 report available at http://www.aapm.org/pubs/reports. Descriptions of the techniques in the clinical sections are not exhaustive but do describe key elements of the procedures and how to initiate these programs in the clinic. There have been no major changes since the TG-25 report relating to flatness and symmetry, surface dose, use of thermoluminescent dosimeters or diodes, virtual source position designation, air gap corrections, oblique incidence, or corrections for inhomogeneities. Thus these topics are not addressed in the TG-70 report.
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Affiliation(s)
- Bruce J Gerbi
- University of Minnesota, Minneapolis, Minnesota 55455, USA.
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Araki F, Hanyu Y, Fukuoka M, Matsumoto K, Okumura M, Oguchi H. Monte Carlo calculations of correction factors for plastic phantoms in clinical photon and electron beam dosimetry. Med Phys 2009; 36:2992-3001. [PMID: 19673198 DOI: 10.1118/1.3151809] [Citation(s) in RCA: 14] [Impact Index Per Article: 0.9] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/07/2022] Open
Abstract
The purpose of this study is to calculate correction factors for plastic water (PW) and plastic water diagnostic-therapy (PWDT) phantoms in clinical photon and electron beam dosimetry using the EGSnrc Monte Carlo code system. A water-to-plastic ionization conversion factor k(pl) for PW and PWDT was computed for several commonly used Farmer-type ionization chambers with different wall materials in the range of 4-18 MV photon beams. For electron beams, a depth-scaling factor c(pl) and a chamber-dependent fluence correction factor h(pl) for both phantoms were also calculated in combination with NACP-02 and Roos plane-parallel ionization chambers in the range of 4-18 MeV. The h(pl) values for the plane-parallel chambers were evaluated from the electron fluence correction factor phi(pl)w and wall correction factors P(wall,w) and P(wall,pl) for a combination of water or plastic materials. The calculated k(pl) and h(pl) values were verified by comparison with the measured values. A set of k(pl) values computed for the Farmer-type chambers was equal to unity within 0.5% for PW and PWDT in photon beams. The k(pl) values also agreed within their combined uncertainty with the measured data. For electron beams, the c(pl) values computed for PW and PWDT were from 0.998 to 1.000 and from 0.992 to 0.997, respectively, in the range of 4-18 MeV. The phi(pl)w values for PW and PWDT were from 0.998 to 1.001 and from 1.004 to 1.001, respectively, at a reference depth in the range of 4-18 MeV. The difference in P(wall) between water and plastic materials for the plane-parallel chambers was 0.8% at a maximum. Finally, h(pl) values evaluated for plastic materials were equal to unity within 0.6% for NACP-02 and Roos chambers. The h(pl) values also agreed within their combined uncertainty with the measured data. The absorbed dose to water from ionization chamber measurements in PW and PWDT plastic materials corresponds to that in water within 1%. Both phantoms can thus be used as a substitute for water for photon and electron dosimetry.
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Affiliation(s)
- Fujio Araki
- Department of Radiological Technology, Kumamoto University School of Health Sciences, 4-24-1, Kuhonji, Kumamoto 862-0976, Japan.
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Zink K, Wulff J. Positioning of a plane-parallel ionization chamber in clinical electron beams and the impact on perturbation factors. Phys Med Biol 2009; 54:2421-35. [DOI: 10.1088/0031-9155/54/8/011] [Citation(s) in RCA: 22] [Impact Index Per Article: 1.5] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/12/2022]
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Chin E, Palmans H, Shipley D, Bailey M, Verhaegen F. Analysis of dose perturbation factors of a NACP-02 ionization chamber in clinical electron beams. Phys Med Biol 2008; 54:307-26. [DOI: 10.1088/0031-9155/54/2/009] [Citation(s) in RCA: 8] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/11/2022]
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31
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Araki F. Monte Carlo calculations of correction factors for plane-parallel ionization chambers in clinical electron dosimetry. Med Phys 2008; 35:4033-40. [DOI: 10.1118/1.2968102] [Citation(s) in RCA: 17] [Impact Index Per Article: 1.1] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/07/2022] Open
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32
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Wang LLW, Rogers DWO. Calculation of the replacement correction factors for ion chambers in megavoltage beams by Monte Carlo simulation. Med Phys 2008; 35:1747-55. [DOI: 10.1118/1.2898139] [Citation(s) in RCA: 38] [Impact Index Per Article: 2.4] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/07/2022] Open
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33
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Wulff J, Zink K, Kawrakow I. Efficiency improvements for ion chamber calculations in high energy photon beams. Med Phys 2008; 35:1328-36. [DOI: 10.1118/1.2874554] [Citation(s) in RCA: 164] [Impact Index Per Article: 10.3] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/07/2022] Open
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Zink K, Wulff J. Monte Carlo calculations of beam quality correction factorskQfor electron dosimetry with a parallel-plate Roos chamber. Phys Med Biol 2008; 53:1595-607. [DOI: 10.1088/0031-9155/53/6/006] [Citation(s) in RCA: 32] [Impact Index Per Article: 2.0] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/11/2022]
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Kapsch RP, Bruggmoser G, Christ G, Dohm OS, Hartmann GH, Schüle E. Experimental determination ofpCoperturbation factors for plane-parallel chambers. Phys Med Biol 2007; 52:7167-81. [DOI: 10.1088/0031-9155/52/23/026] [Citation(s) in RCA: 6] [Impact Index Per Article: 0.4] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/11/2022]
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36
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Araki F. Monte Carlo study of correction factors for the use of plastic phantoms in clinical electron dosimetry. Med Phys 2007; 34:4368-77. [DOI: 10.1118/1.2790840] [Citation(s) in RCA: 8] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/07/2022] Open
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Abstract
Silicon semiconductor diodes measure almost the same depth-dose distributions in both photon and electron beams as those measured by ion chambers. A recent study in ion chamber dosimetry has suggested that the wall correction factor for a parallel-plate ion chamber in electron beams changes with depth by as much as 6%. To investigate diode detector response with respect to depth, a silicon diode model is constructed and the water/silicon dose ratio at various depths in electron beams is calculated using EGSnrc. The results indicate that, for this particular diode model, the diode response per unit water dose (or water/diode dose ratio) in both 6 and 18 MeV electron beams is flat within 2% versus depth, from near the phantom surface to the depth of R50 (with calculation uncertainty <0.3%). This suggests that there must be some other correction factors for ion chambers that counter-balance the large wall correction factor at depth in electron beams. In addition, the beam quality and field-size dependence of the diode model are also calculated. The results show that the water/diode dose ratio remains constant within 2% over the electron energy range from 6 to 18 MeV. The water/diode dose ratio does not depend on field size as long as the incident electron beam is broad and the electron energy is high. However, for a very small beam size (1 X 1 cm(2)) and low electron energy (6 MeV), the water/diode dose ratio may decrease by more than 2% compared to that of a broad beam.
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Affiliation(s)
- Lilie L W Wang
- Physics Department, Carleton University, Ottawa KIS 5B6, Canada
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38
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McEwen M, Palmans H, Williams A. An empirical method for the determination of wall perturbation factors for parallel-plate chambers in high-energy electron beams. Phys Med Biol 2006; 51:5167-81. [PMID: 17019031 DOI: 10.1088/0031-9155/51/20/006] [Citation(s) in RCA: 9] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/12/2022]
Abstract
The calibration of ion chambers in high-energy electron beams in terms of absorbed dose to water at the National Physical Laboratory requires knowledge of the ratio of perturbation factors in graphite and water phantoms. During a review of data required for the NPL calibration procedure an empirical model was developed to calculate the perturbation due to the rear wall, pwall, of a well-guarded ion chamber in a high-energy electron beam. The overall uncertainty in this method is estimated to be 0.4%, which is the lowest value reported to date. The model reproduces measured data at the 0.1% level or better and indicates that the NACP ion chamber has a nonzero perturbation factor in electron beams due to backscatter from the rear wall. The effect is small (<0.5%) at high energies (R50>4 cm, E0>10 MeV) but becomes large at low energies-up to 1.4% at E0=4 MeV (R50=1.2 cm). The model indicates that there is a nonzero correction for the NACP chamber in both a graphite and water phantom and that material adjacent to the air cavity has a significant effect on the measured ionization. These values are consistent with previous measurements and recent Monte Carlo calculations. The model could be used in the design of ion chambers and in the estimation of corrections for non-homogeneous systems, especially in the absence of accurate Monte Carlo simulations.
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Affiliation(s)
- Malcolm McEwen
- Ionizing Radiation Standards, National Research Council, Ottawa, Canada.
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