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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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Bourgouin A, Paz-Martín J, Gedik YC, Frei F, Peier P, Rossomme S, Schönfeld AA, Schüller A, Rodriguez FG, Kapsch RP. Charge collection efficiency of commercially available parallel-plate ionisation chambers in ultra-high dose-per-pulse electron beams. Phys Med Biol 2023; 68:235002. [PMID: 37934049 DOI: 10.1088/1361-6560/ad0a58] [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: 08/07/2023] [Accepted: 11/07/2023] [Indexed: 11/08/2023]
Abstract
Objective. This investigation aims to experimentally determine the charge collection efficiency (CCE) of six commercially available parallel-plate ionisation chamber (PPIC) models in ultra-high dose-per-pulse (UHDPP) electron beams.Approach. The CCE of 22 PPICs has been measured in UHDPP electron beams at the National Metrology Institution of Germany (PTB). The CCE was determined for a dose per pulse (DPP) range between 0.1 and 6.4 Gy (pulse duration of 2.5μs). The results obtained with the different PPICs were compared to evaluate the reproducibility, intra- and inter-model variation, and the performance of a CCE empirical model.Main results. The intra-model variation was, on average, 4.0%, which is more than three times the total combined relative standard uncertainty and was found to be greater at higher DPP (up to 20%). The inter-model variation for the PPIC with 2 mm electrode spacing, which was found to be, on average, 10%, was also significant compared to the relative uncertainty and the intra-model variation. The observed CCE variation could not be explained only by the expected deviation of the electrode spacing from the nominal value within the manufacturing tolerance. It should also be noted that a substantial polarity effect, between 0.914(5) and 1.201(3), was observed, and significant intra- and inter-model variation was observed on this effect.Significance. For research and pre-clinical study, the commercially available PPIC with a well-known CCE (directly measured for the specific chamber) and with a small electrode spacing could be used for relative and absolute dosimetry with a lower-limit uncertainty of 1.6% (k= 1) in the best case. However, to use a PPIC as a secondary standard in UHDPP electron beams for clinical purposes would require new model development to reduce the ion recombination, the polarity effect, and the total standard uncertainty on the dose measurement.
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Affiliation(s)
- Alexandra Bourgouin
- Dosimetry for Radiation Therapy and Diagnostic Radiology, Physikalisch-Technische Bundesanstalt (PTB), Braunschweig, Germany
| | - Jose Paz-Martín
- Departamento de Física de Partículas, Universidad de Santiago, Santiago de Compostela, Spain
| | - Yunus Can Gedik
- Nuclear Energy Research Institute (NÜKEN), Turkish Energy Nuclear and Mineral Research Agency (TENMAK), Ankara, Turkey
| | - Franziska Frei
- Eidgenössisches Institut für Metrologie (METAS), Bern-Wabern, Switzerland
| | - Peter Peier
- Eidgenössisches Institut für Metrologie (METAS), Bern-Wabern, Switzerland
| | | | - Andreas A Schönfeld
- Sun Nuclear, A Mirion Medical Company, Melbourne, FL, United States of America
| | - Andreas Schüller
- Dosimetry for Radiation Therapy and Diagnostic Radiology, Physikalisch-Technische Bundesanstalt (PTB), Braunschweig, Germany
| | | | - Ralf-Peter Kapsch
- Dosimetry for Radiation Therapy and Diagnostic Radiology, Physikalisch-Technische Bundesanstalt (PTB), Braunschweig, Germany
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Fagerstrom JM. Dosimetric characterization of foam padding with posterior fields in palliative radiation therapy. Med Dosim 2023; 49:65-68. [PMID: 37673727 DOI: 10.1016/j.meddos.2023.08.003] [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: 03/29/2023] [Revised: 06/12/2023] [Accepted: 08/09/2023] [Indexed: 09/08/2023]
Abstract
Patients undergoing external beam radiation therapy for the palliative treatment of painful bony metastases may have difficulty maintaining a still position on a rigid uncovered couch top, both during CT simulation as well as during patient setup, image guidance, and treatment on the linear accelerator. For these patients, a thin foam pad or mattress is sometimes used to mitigate patient discomfort. It was desired to quantify the effect of the padding in cases in which the patient is to be treated supine with posterior beams when the majority of the beam weighting traverses both the couch and the pad. Ion chamber measurements in-phantom were acquired with 6 MV, 10 MV, and 15 MV photon beams. At depths of maximum dose, the pad resulted in a difference of signal collected ≤1%. At the phantom surface, the pad resulted in an increase in signal ranging from 1% to 6.5% for the measured beams. CT data of the pad, both with and without applied pressure, indicated that the pad had average HU values close to air.
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Affiliation(s)
- Jessica M Fagerstrom
- Northwest Medical Physics Center, Lynnwood, WA, 98036; Kaiser Permanente, Seattle, WA, 98112.
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Khan AU, Nelson NP, Culberson WS, DeWerd LA. On the perturbation effect and LET dependence of beam quality correction factors in carbon ion beams. Med Phys 2023; 50:1105-1120. [PMID: 36334024 DOI: 10.1002/mp.16089] [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: 01/19/2022] [Revised: 05/31/2022] [Accepted: 10/26/2022] [Indexed: 11/06/2022] Open
Abstract
BACKGROUND In a recent study, we reported beam quality correction factors, fQ , in carbon ion beams using Monte Carlo (MC) methods for a cylindrical and a parallel-plate ionization chamber (IC). A non-negligible perturbation effect was observed; however, the magnitude of the perturbation correction due to the specific IC subcomponents was not included. Furthermore, the stopping power data presented in the International Commission on Radiation Units and Measurements (ICRU) report 73 were used, whereas the latest stopping power data have been reported in the ICRU report 90. PURPOSE The aim of this study was to extend our previous work by computing fQ correction factors using the ICRU 90 stopping power data and by reporting IC-specific perturbation correction factors. Possible energy or linear energy transfer (LET) dependence of the fQ correction factor was investigated by simulating both pristine beams and spread-out Bragg peaks (SOBPs). METHODS The TOol for PArticle Simulation (TOPAS)/GEANT4 MC code was used in this study. A 30 × 30 × 50 cm3 water phantom was simulated with a uniform 10 × 10 cm2 parallel beam incident on the surface. A Farmer-type cylindrical IC (Exradin A12) and two parallel-plate ICs (Exradin P11 and A11) were simulated in TOPAS using the manufacturer-provided geometrical drawings. The fQ correction factor was calculated in pristine carbon ion beams in the 150-450 MeV/u energy range at 2 cm depth and in the middle of the flat region of four SOBPs. The kQ correction factor was calculated by simulating the fQo correction factor in a 60 Co beam at 5 cm depth. The perturbation correction factors due to the presence of the individual IC subcomponents, such as the displacement effect in the air cavity, collecting electrode, chamber wall, and chamber stem, were calculated at 2 cm depth for monoenergetic beams only. Additionally, the mean dose-averaged and track-averaged LET was calculated at the depths at which the fQ was calculated. RESULTS The ICRU 90 fQ correction factors were reported. The pdis correction factor was found to be significant for the cylindrical IC with magnitudes up to 1.70%. The individual perturbation corrections for the parallel-plate ICs were <1.0% except for the A11 pcel correction at the lowest energy. The fQ correction for the P11 IC exhibited an energy dependence of >1.00% and displayed differences up to 0.87% between pristine beams and SOBPs. Conversely, the fQ for A11 and A12 displayed a minimal energy dependence of <0.50%. The energy dependence was found to manifest in the LET dependence for the P11 IC. A statistically significant LET dependence was found only for the P11 IC in pristine beams only with a magnitude of <1.10%. CONCLUSIONS The perturbation and kQ correction factor should be calculated for the specific IC to be used in carbon ion beam reference dosimetry as a function of beam quality.
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Affiliation(s)
- Ahtesham Ullah Khan
- Department of Medical Physics, School of Medicine and Public Health, University of Wisconsin-Madison, Madison, Wisconsin, USA
| | - Nicholas P Nelson
- Department of Medical Physics, School of Medicine and Public Health, University of Wisconsin-Madison, Madison, Wisconsin, USA
| | - Wesley S Culberson
- Department of Medical Physics, School of Medicine and Public Health, University of Wisconsin-Madison, Madison, Wisconsin, USA
| | - Larry A DeWerd
- Department of Medical Physics, School of Medicine and Public Health, University of Wisconsin-Madison, Madison, Wisconsin, USA
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Muir B, Culberson W, Davis S, Kim GGY, Lee SW, Lowenstein J, Renaud J, Sarfehnia A, Siebers J, Tantôt L, Tolani N. AAPM WGTG51 Report 374: Guidance for TG-51 reference dosimetry. Med Phys 2022; 49:6739-6764. [PMID: 36000424 DOI: 10.1002/mp.15949] [Citation(s) in RCA: 6] [Impact Index Per Article: 3.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/20/2021] [Revised: 07/21/2022] [Accepted: 07/27/2022] [Indexed: 12/13/2022] Open
Abstract
Practical guidelines that are not explicit in the TG-51 protocol and its Addendum for photon beam dosimetry are presented for the implementation of the TG-51 protocol for reference dosimetry of external high-energy photon and electron beams. These guidelines pertain to: (i) measurement of depth-ionization curves required to obtain beam quality specifiers for the selection of beam quality conversion factors, (ii) considerations for the dosimetry system and specifications of a reference-class ionization chamber, (iii) commissioning a dosimetry system and frequency of measurements, (iv) positioning/aligning the water tank and ionization chamber for depth ionization and reference dose measurements, (v) requirements for ancillary equipment needed to measure charge (triaxial cables and electrometers) and to correct for environmental conditions, and (vi) translation from dose at the reference depth to that at the depth required by the treatment planning system. Procedures are identified to achieve the most accurate results (errors up to 8% have been observed) and, where applicable, a commonly used simplified procedure is described and the impact on reference dosimetry measurements is discussed so that the medical physicist can be informed on where to allocate resources.
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Affiliation(s)
- Bryan Muir
- Metrology Research Centre, National Research Council of Canada, Ottawa, Ontario, Canada
| | - Wesley Culberson
- Department of Medical Physics, University of Wisconsin - Madison, Madison, Wisconsin, United States
| | - Stephen Davis
- Radiation Oncology, Miami Cancer Institute, Miami, Florida, United States
| | - Grace Gwe-Ya Kim
- Department of Radiation Medicine and Applied Sciences, UC San Diego School of Medicine, La Jolla, California, United States
| | - Sung-Woo Lee
- Department of Radiation Oncology, University of Maryland School of Medicine, Columbia, Maryland, United States
| | - Jessica Lowenstein
- Department of Radiation Physics, UT M.D. Anderson Cancer Center, Houston, Texas, United States
| | - James Renaud
- Metrology Research Centre, National Research Council of Canada, Ottawa, Ontario, Canada
| | - Arman Sarfehnia
- Department of Radiation Oncology, University of Toronto, Toronto, Ontario, Canada
| | - Jeffrey Siebers
- Department of Radiation Oncology, University of Virginia Health System, Charlottesville, Virginia, United States
| | - Laurent Tantôt
- Département de radio-oncologie, CIUSSS de l'Est-de-l'Île-de-Montréal - Hôpital Maisonneuve-Rosemont, Montreal, Quebec, Canada
| | - Naresh Tolani
- Department of Radiation Therapy, Michael E. DeBakey VA Medical Center, Houston, Texas, United States
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Begg J, Jelen U, Keall P, Liney G, Holloway L. Experimental characterisation of the magnetic field correction factor,kB⃗,for Roos chambers in a parallel MRI-linac. Phys Med Biol 2022; 67. [PMID: 35413694 DOI: 10.1088/1361-6560/ac66b8] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/25/2021] [Accepted: 04/12/2022] [Indexed: 12/15/2022]
Abstract
Objective.Reference dosimetry on an MRI-linac requires a chamber specific magnetic field correction factor,kB⃗.This work aims to measure the correction factor for a parallel plate chamber on a parallel MRI-linac.Approach.kB⃗is defined as the ratio of the absorbed dose to water calibration coefficient in the presence of the magnetic field,ND,wB⃗relative to that under 0 T conditions,ND,w0T.kB⃗was measured via aND,wtransfer to a field chamber at each magnetic field strength from a chamber with knownND,wandkB⃗.This was achieved on the parallel MRI-linac by moving the measurement set-up between a high magnetic field strength region at the MRI-isocentre and a low magnetic field strength region at the end of the bore whilst maintaining consistent set-up and scatter conditions. Three PTW 34001 Roos chambers were investigated as well as a PTW 30013 Farmer used to validate methodology.Main Results.The beam quality used for the measurements ofkB⃗wasTPR20/10 = 0.632. ThekB⃗for the PTW Farmer chamber at 1 T on a parallel MRI-linac was 0.993 ± 0.013 (k = 1). The averagekB⃗factor measured for the three Roos chambers on a 1 T parallel MRI-linac was 0.999 ± 0.014 (k = 1).Significance.The results presented are the first measurements ofkB⃗for a Roos chamber on a parallel MRI-linac. The Roos chamber results demonstrate the potential for the chamber as a reference dosimeter in parallel MRI-linacs.
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Affiliation(s)
- Jarrad Begg
- Department of Medical Physics, Liverpool and Macarthur Cancer Therapy Centre, Liverpool, NSW, 2170, Australia.,Ingham Institute for Applied Medical Research, Liverpool, NSW, 2170, Australia.,South Western Sydney Clinical School, University of New South Wales, Liverpool, NSW, 2170, Australia
| | - Urszula Jelen
- Ingham Institute for Applied Medical Research, Liverpool, NSW, 2170, Australia
| | - Paul Keall
- Ingham Institute for Applied Medical Research, Liverpool, NSW, 2170, Australia.,Image X Institute, Faculty of Medicine and Health, University of Sydney, Camperdown, NSW, 2005, Australia
| | - Gary Liney
- Department of Medical Physics, Liverpool and Macarthur Cancer Therapy Centre, Liverpool, NSW, 2170, Australia.,Ingham Institute for Applied Medical Research, Liverpool, NSW, 2170, Australia.,South Western Sydney Clinical School, University of New South Wales, Liverpool, NSW, 2170, Australia.,Centre for Medical Radiation Physics, University of Wollongong, Wollongong, NSW, 2522, Australia
| | - Lois Holloway
- Department of Medical Physics, Liverpool and Macarthur Cancer Therapy Centre, Liverpool, NSW, 2170, Australia.,Ingham Institute for Applied Medical Research, Liverpool, NSW, 2170, Australia.,South Western Sydney Clinical School, University of New South Wales, Liverpool, NSW, 2170, Australia.,Centre for Medical Radiation Physics, University of Wollongong, Wollongong, NSW, 2522, Australia.,Institute of Medical Physics, University of Sydney, Camperdown, NSW, 2005, Australia
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Aldosary G, Belec J, Foottit C, Vandervoort E. Dosimetric considerations for moldable silicone composites used in radiotherapy applications. J Appl Clin Med Phys 2022; 23:e13605. [PMID: 35436377 PMCID: PMC9195024 DOI: 10.1002/acm2.13605] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/28/2021] [Revised: 11/18/2021] [Accepted: 03/09/2022] [Indexed: 12/03/2022] Open
Abstract
Due to their many favorable characteristics, moldable silicone (MS) composites have gained popularity in medicine and recently, in radiotherapy applications. We investigate the dosimetric properties of silicones in radiotherapy beams and determine their suitability as water substitutes for constructing boluses and phantoms. Two types of silicones were assessed (ρ= 1.04 g/cm3 and ρ= 1.07 g/cm3). Various dosimetric properties were characterized, including the relative electron density, the relative mean mass energy‐absorption coefficient, and the relative mean mass restricted stopping power. Silicone slabs with thickness of 1.5 cm and 5.0 cm were molded to mimic a bolus setup and a phantom setup, respectively. Measurements were conducted for Co‐60 and 6 MV photon beams, and 6 MeV electron beams. The doses at 1.5 cm and 5.0 cm depths in MS were measured with solid water (SW) backscatter material (DMS–SW), and with a full MS setup (DMS–MS), then compared with doses at the same depths in a full SW setup (DSW–SW). Relative doses were reported as DMS–SW/DMS–SW and DMS–MS/DSW–SW. Experimental results were verified using Monaco treatment planning system dose calculations and Monte Carlo EGSnrc simulations. Film measurements showed varying dose ratios according to MS and beam types. For photon beams, the bolus setup DMS–SW/DSW–SW exhibited a 5% relative dose reduction. The dose for 6 MV beams was reduced by nearly 2% in a full MS setup. Up to 2% dose increase in both scenarios was observed for electron beams. Compared with dose in SW, an interface of MS–SW can cause relatively high differences. We conclude that it is important to characterize a particular silicone's properties in a given beam quality prior to clinical use. Because silicone compositions vary between manufacturers and differ from water/SW, accurate dosimetry using these materials requires consideration of the reported differences.
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Affiliation(s)
- Ghada Aldosary
- Department of Physics, Carleton University, Ottawa, Ontario, Canada.,Radiation Oncology Section, Department of Oncology, King Abdulaziz Medical City, National Guard Health Affairs, Riyadh, Saudi Arabia
| | - Jason Belec
- Department of Medical Physics, The Ottawa Hospital Cancer Centre, Ottawa, Ontario, Canada.,Department of Medicine, The University of Ottawa, Ottawa, Ontario, Canada
| | - Claire Foottit
- Department of Medical Physics, The Ottawa Hospital Cancer Centre, Ottawa, Ontario, Canada.,Department of Medicine, The University of Ottawa, Ottawa, Ontario, Canada
| | - Eric Vandervoort
- Department of Physics, Carleton University, Ottawa, Ontario, Canada.,Department of Medical Physics, The Ottawa Hospital Cancer Centre, Ottawa, Ontario, Canada.,Department of Medicine, The University of Ottawa, Ottawa, Ontario, Canada
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Pawiro SA, Mahfirotin DA, Assegab MI, Wibowo WE. Modified electron beam output calibration based on IAEA Technical Report Series 398. J Appl Clin Med Phys 2022; 23:e13573. [PMID: 35226389 PMCID: PMC8992941 DOI: 10.1002/acm2.13573] [Citation(s) in RCA: 3] [Impact Index Per Article: 1.5] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/18/2021] [Revised: 02/05/2022] [Accepted: 02/11/2022] [Indexed: 11/24/2022] Open
Abstract
Purpose The recently worldwide standard measurement of electron beam reference dosimetry include the International Atomic Energy Agency (IAEA) Technical Report Series (TRS)‐398 and Association of Physicists in Medicine (AAPM) Task Group (TG)‐51 protocols. Muir et al. have modified calibration methods for electron beam calibration based on AAPM TG‐51. They found that the use of cylindrical chambers at low energy gave acceptable results. In this study, we propose and report a modified calibration for electron beam based on IAEA TRS‐398, the standard reference dosimetry protocol worldwide. Methods This work was carried out with energies of 6, 8, 10, 12, and 15 MeV. The electron beam is generated from Elektra Synergy Platform and Versa HD linear accelerator. The charge readings were measured with PTW 30013, IBA CC13, Exradin A1Sl, and Exradin A11 chambers connected to the electrometer. The dose calculation uses an equation of modified calibration for electron beam using the updated kQ factor in previous work. The absorbed dose to water for electron beam is expressed in dose per monitor unit (cGy/MU). Thus, we compared dose per monitor unit (D/MU) calculation using a modified calibration to TRS‐398. Results In this work, we have succeeded in implementing the modified calibration of electron beam based on TRS‐398 by applying a cylindrical chamber in all energy beams and using the updated kQ factor. The ratio of the absorbed dose to water between original and modified calibration protocols of TRS‐398 (Dw) for the cylindrical chamber was 1.002 on the Elekta Synergy Platform and 1.000 on the Versa HD while for the parallel‐plate chamber it was 1.013 on the Elekta Synergy Platform and 1.014 on the Versa HD. Based on these results, both the cylindrical and parallel‐plate chambers are still within the tolerance limit allowed by the TRS‐398 protocol, which is ±2%. Therefore, modified calibration based on TRS‐398 gives acceptable results and is simpler to use clinically.
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Affiliation(s)
- Supriyanto Ardjo Pawiro
- Department of Physics, Faculty of Mathematics and Natural Sciences, Universitas Indonesia, Depok, West Java, Indonesia
| | - Dwi Aprilia Mahfirotin
- Department of Physics, Faculty of Mathematics and Natural Sciences, Universitas Indonesia, Depok, West Java, Indonesia
| | - Muhamad Iqbal Assegab
- Department of Radiation Oncology, Dr. Cipto Mangunkusumo National General Hospital, Jakarta, Indonesia
| | - Wahyu Edy Wibowo
- Department of Radiation Oncology, Dr. Cipto Mangunkusumo National General Hospital, Jakarta, Indonesia
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Surface dose and build-up region depth dose measurements in non-standard beams of Cyberknife and tomotherapy systems. Radiol Phys Technol 2021; 14:309-317. [PMID: 34224082 DOI: 10.1007/s12194-021-00629-z] [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: 10/16/2020] [Revised: 06/26/2021] [Accepted: 06/28/2021] [Indexed: 10/20/2022]
Abstract
The purpose of this study was to measure the surface dose and build-up region depth dose characteristics of 6 MV photon beams in Cyberknife and helical tomotherapy (HT) systems for non-standard small fields using parallel plate chambers (Roos and Markus), Gafchromic EBT3 films, and nanoDot optically stimulated luminescence dosimeters (OSLDs), as well as to investigate the effect of oblique incidence on the surface dose of the beam. All measurements were conducted in a virtual water phantom under machine-specific reference conditions. The Roos and OSLDs overestimated the surface dose when compared with the Markus chamber and EBT3 films by 20%. We applied water equivalent thickness (WET) correction to account for the intrinsic build-up thickness of the detectors from their effective point of measurement (EPOM). With WET correction, a reasonably close surface dose estimate was obtained for all detectors, within 1.9% agreement for the 60 mm collimator of Cyberknife and 3.1% agreement for the HT system, with a 5 × 10 cm2 field size. The surface dose increased from the normally incident Cyberknife and HT fields with increasing angle of incidence. The surface dose increased to twice its value at normal incidence for highly oblique angles of incidence above 55°. For the tested fields, a reasonable surface dose estimate could be measured with the detectors if the correction for intrinsic buildup thickness was applied. Nevertheless, the use of Roos chambers with large dimensions and nanoDot OSLDs is not recommended for estimating the surface dose for small fields.
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Performance characteristics of some cylindrical ion chamber dosimeters in Megavoltage (MV) photon beam according to TRS-398 dosimetry protocol. Radiat Phys Chem Oxf Engl 1993 2021. [DOI: 10.1016/j.radphyschem.2020.109299] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/08/2023]
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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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12
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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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13
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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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Guida F, Barbato A, Ciocca M, Schwarz M, Lorentini S, Mastella E, Cirrone GAP, Petringa G, Liotta M, Tarabelli De Fatis P, Masi M, Mettivier G, Russo P. Dose intercomparison at Italian hadrontherapy centers. Phys Med 2019; 68:83-87. [PMID: 31765885 DOI: 10.1016/j.ejmp.2019.11.009] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.2] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 07/07/2019] [Revised: 11/12/2019] [Accepted: 11/13/2019] [Indexed: 11/18/2022] Open
Abstract
PURPOSE To perform the first dosimetric intercomparison for proton beams in Italy using ionization chambers, according to the IAEA TRS-398 code of practice. METHODS Measurement sites included: National Center for Oncological Hadron Therapy (CNAO, Pavia), Center for Proton Therapy (CTP, Trento) and Center for Hadron Therapy and for advanced Nuclear Applications (CATANA, Catania). For comparison we also included a 6 MV photon beam produced at Istituti Clinici Scientifici Maugeri (ICSM, Pavia). For proton beams, both single pseudo-monoenergetic layers (in order to obtain a planned dose of 2 Gy at the reference depth of 2 cm in a water phantom) and Spread-out Bragg peaks (SOBP) have been delivered. Measurements were performed with a PTW Farmer 30010-1 and a PTW Advanced Markus type 34,045 ionization chamber. RESULTS Data obtained at CATANA, CNAO and CPT in terms of absorbed dose to water depth show good consistency within the experimental uncertainties, with a weighted mean of 1.99 ± 0.01 Gy and a standard error of 0.003 Gy, with reference to a nominal dose of 2 Gy as designed by the treatment planning system. CONCLUSIONS The results showed a standard deviation of less than 1% for single layer and SOBP beams, for all chambers and a percent deviation less than 1.5% for single layer measurements. The weighted means of the absorbed doses for clinical proton beams (118.19 MeV and 173.61 MeV) are consistent within less than 1%. These results agree within the 1.5% difference considered acceptable for national dose intercomparison.
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Affiliation(s)
- F Guida
- Università di Napoli Federico II, Dipartimento di Fisica "Ettore Pancini", Napoli, Italy; INFN Sezione di Napoli, Napoli, Italy
| | - A Barbato
- Università di Napoli Federico II, Dipartimento di Fisica "Ettore Pancini", Napoli, Italy; INFN Sezione di Napoli, Napoli, Italy
| | | | - M Schwarz
- Centro di Protonterapia, APSS, Trento, Italy
| | - S Lorentini
- Centro di Protonterapia, APSS, Trento, Italy
| | | | | | - G Petringa
- INFN-LNS, Catania, Italy; Università di Catania, Dipartimento di Fisica ed Astronomia, Catania, Italy
| | - M Liotta
- Istituti Clinici Scientifici Maugeri, Pavia, Italy
| | | | - M Masi
- Università di Napoli Federico II, Dipartimento di Fisica "Ettore Pancini", Napoli, Italy; INFN Sezione di Napoli, Napoli, Italy
| | - G Mettivier
- Università di Napoli Federico II, Dipartimento di Fisica "Ettore Pancini", Napoli, Italy; INFN Sezione di Napoli, Napoli, Italy.
| | - P Russo
- Università di Napoli Federico II, Dipartimento di Fisica "Ettore Pancini", Napoli, Italy; INFN Sezione di Napoli, Napoli, Italy
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15
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Bourgouin A, Cojocaru C, Ross C, McEwen M. Determination of
W
air
in high‐energy electron beams using graphite detectors. Med Phys 2019; 46:5195-5208. [DOI: 10.1002/mp.13772] [Citation(s) in RCA: 5] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/02/2019] [Revised: 07/09/2019] [Accepted: 08/01/2019] [Indexed: 11/09/2022] Open
Affiliation(s)
- Alexandra Bourgouin
- Department of Physics Carleton University Ottawa ON K1S 5B6 Canada
- Ionizing Radiation Standards National Research Council of Canada Ottawa ON K1A 0R6Canada
| | - Claudiu Cojocaru
- Ionizing Radiation Standards National Research Council of Canada Ottawa ON K1A 0R6Canada
| | - Carl Ross
- Ionizing Radiation Standards National Research Council of Canada Ottawa ON K1A 0R6Canada
| | - Malcolm McEwen
- Ionizing Radiation Standards National Research Council of Canada Ottawa ON K1A 0R6Canada
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16
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Gomà C, Sterpin E. Monte Carlo calculation of beam quality correction factors in proton beams using PENH. ACTA ACUST UNITED AC 2019; 64:185009. [DOI: 10.1088/1361-6560/ab3b94] [Citation(s) in RCA: 16] [Impact Index Per Article: 3.2] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/12/2022]
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17
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Bruggmoser G, Saum R, Kranzer R. Determination of recombination and polarity correction factors, k S and k P , for small cylindrical ionization chambers PTW 31021 and PTW 31022 in pulsed filtered and unfiltered beams. Z Med Phys 2018; 28:247-253. [DOI: 10.1016/j.zemedi.2017.09.010] [Citation(s) in RCA: 8] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/05/2017] [Revised: 09/20/2017] [Accepted: 09/20/2017] [Indexed: 01/08/2023]
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18
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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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19
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Howard ME, Beltran C, Anderson S, Tseung WC, Sarkaria JN, Herman MG. Investigating Dependencies of Relative Biological Effectiveness for Proton Therapy in Cancer Cells. Int J Part Ther 2018; 4:12-22. [PMID: 30159358 DOI: 10.14338/ijpt-17-00031.1] [Citation(s) in RCA: 24] [Impact Index Per Article: 4.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/25/2022] Open
Abstract
Purpose Relative biological effectiveness (RBE) accounts for the differences in biological effect from different radiation types. The RBE for proton therapy remains uncertain, as it has been shown to vary from the clinically used value of 1.1. In this work we investigated the RBE of protons and correlated the biological differences with the underlying physical quantities. Materials and Methods Three cell lines were irradiated (CHO, Chinese hamster ovary; A549, human lung adenocarcinoma; and T98, human glioma) and assessed for cell survival by using clonogenic assay. Cells were irradiated with 71- and 160-MeV protons at depths along the Bragg curve and 6-MV photons to various doses. The dose-averaged lineal energy ( y‒D ) was measured under similar conditions as the cells by using a microdosimeter. Dose-averaged linear energy transfer (LETd) was also calculated by using Monte Carlo (MC) simulations. Survival data were fit by using the linear quadratic model. The RBE values were calculated by comparing the physical dose (D6MV/Dp) that results in 50% (RBE0.5) and 10% (RBE0.1) cell survival, and survival after 2 Gy (RBE2Gy). Results Proton RBE values ranged from 0.89 to 2.40. The RBE for all 3 cell lines increased with decreasing proton energy and was higher at 50% survival than at 10% survival. Additionally, both A549 and T98 cells generally had higher RBE values relative to the CHO cells, indicating a greater biological response to protons. An increase in RBE corresponded with an increase in y‒D and LETd. Conclusion Proton RBE was found to depend on mean proton energy, survival end point, and cell type. Changes in both y‒D and LETd were also found to impact proton RBE values, but consideration of the energy spectrum may provide additional information. The RBE values in this study vary greatly, indicating the clinical value of 1.1 may not be suitable in all cases.
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Affiliation(s)
| | - Chris Beltran
- Department of Radiation Oncology, Mayo Clinic, Rochester, MN, USA
| | - Sarah Anderson
- Department of Radiation Oncology, Mayo Clinic, Rochester, MN, USA
| | - Wan Chan Tseung
- Department of Radiation Oncology, Mayo Clinic, Rochester, MN, USA
| | - Jann N Sarkaria
- Department of Radiation Oncology, Mayo Clinic, Rochester, MN, USA
| | - Michael G Herman
- Department of Radiation Oncology, Mayo Clinic, Rochester, MN, USA
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20
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Malkov VN, Rogers DWO. Monte Carlo study of ionization chamber magnetic field correction factors as a function of angle and beam quality. Med Phys 2018; 45:908-925. [DOI: 10.1002/mp.12716] [Citation(s) in RCA: 45] [Impact Index Per Article: 7.5] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/30/2017] [Revised: 10/31/2017] [Accepted: 11/25/2017] [Indexed: 11/08/2022] Open
Affiliation(s)
- Victor N. Malkov
- Carleton Laboratory for Radiotherapy Physics; Physics Dept; Carleton University; Ottawa ON Canada
| | - D. W. O. Rogers
- Carleton Laboratory for Radiotherapy Physics; Physics Dept; Carleton University; Ottawa ON Canada
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21
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Lee J, Ye SJ. Abstract ID: 13 Monte Carlo simulations for the beam quality factors of a parallel-plate ion-chamber in the presence of magnetic field. Phys Med 2018; 45 Suppl 1:S1. [PMID: 29413848 DOI: 10.1016/j.ejmp.2017.11.024] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Indexed: 10/18/2022] Open
Abstract
Magnetic resonance imaging-guided radiotherapy provides real-time imaging with a superior soft-tissue contrast without radiation exposure. Recently, several groups have been developing such a new technology. Strong magnetic fields can influence trajectories of the secondary electrons by the Lorentz force. The reference dosimetry using an ion-chamber in magnetic fields needs additional correction factors [1]. In this study, we calculated magnetic field correction factors by the Monte Carlo method for the reference dosimetry using a parallel-plate ion-chamber. The EGSnrc user code, egs_chamber was used to simulate an ion-chamber. The full head and spectral source models of Varian therapeutic linear accelerator of 6 MV, 10 MV, and 15 MV photon beam have been simulated by BEAMnrc and beamdp. A parallel-plate ion-chamber (NACP-02 model) was positioned in the water phantom (30 × 30 × 30 cm3) at a depth of 10 cm (5 cm for Co-60 beam). The beam quality factors (KQ) and magnetic field correction factors (KQ,B) were calculated. The absorbed dose of a parallel-plate ion-chamber was scored with and without a 1.5 T of magnetic field. The KQ of 6 MV, 10 MV, and 15 MV were 0.994, 0.980, and 0.976, respectively. These values were compatible to the previous published data (<0.3%) [2]. In a 1.5 T of magnetic field, the KQ,B of 6, 10, and 15 MV were 0.935, 0.985, and 0.994, respectively, compared to 0.975, 0.983, and 0.983 in a 0.35 T of magnetic field. All of simulation uncertainties were within 0.2%. When photon energy increases, KQ,B is also increased, but KQ,B in high strength of a magnetic field are not always smaller than those in low strength of a magnetic field. The magnetic field correction factors of a parallel-plate ion-chamber were successfully calculated by the Monte Carlo method. The parallel-plate ion-chambers need several percent of correction factors when measuring doses in the presence of a magnetic field.
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Affiliation(s)
- Jaegi Lee
- Program in Biomedical Radiation Sciences, Department of Transdisciplinary Studies, Graduate School of Convergence Science and Technology, Seoul National University, Seoul, Republic of Korea
| | - Sung-Joon Ye
- Program in Biomedical Radiation Sciences, Department of Transdisciplinary Studies, Graduate School of Convergence Science and Technology, Seoul National University, Seoul, Republic of Korea
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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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23
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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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24
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Malkov VN, Rogers DWO. Sensitive volume effects on Monte Carlo calculated ion chamber response in magnetic fields. Med Phys 2017. [PMID: 28636763 DOI: 10.1002/mp.12421] [Citation(s) in RCA: 33] [Impact Index Per Article: 4.7] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/11/2022] Open
Abstract
PURPOSE The development of magnetic resonance-guided radiation therapy (MRgRT) necessitates accurate Monte Carlo (MC) models of ion chambers for computing ion chamber corrections to compensate for the presence of the magnetic field. This study evaluates the sensitivity of the ion chamber dose response in a magnetic field on the collection volume used in the MC simulation. METHODS The EGSnrc system's egs_chamber application is used with a recently developed and validated magnetic field transport code. The calculated dose to the sensitive volume of the chamber per unit incident photon fluence, normalized to that at 0 T, is evaluated as a function of magnetic field for the PTW 30013, PTW 31006, PTW 31010, Exradin A12S, and Exradin A1SL chambers. The sensitive region is varied by excluding the volume corresponding to either 0, 0.5, or 1 mm of distance away from the stem. The photon field, magnetic field, and ion chamber are all oriented perpendicular to each other as in the majority of published experimental works. RESULTS The calculations for a Co-60 source demonstrate that variations from the 0 mm simulations are on the order of several percent with a maximum deviation, occurring at 0.5 T, of 1.75 ± 0.03% and 3.39 ± 0.06% for the 0.5 mm or 1 mm simulations, respectively, for a 0.057 cm3 A1SL chamber. Larger volume chambers showed smaller, but still non-negligible, variations. Simulations of the A1SL chamber with a 7 MV photon source, corresponding to the Elekta MR-linac machine, demonstrate that the effect is slightly reduced but still persists with a maximum deviation of 1.97 ± 0.08% for the 1 mm reduction. CONCLUSIONS Usually, the geometric sensitive volume of the ion chamber is used in MC calculation as a substitute for the potentially unknown, smaller, true collection volume (governed by the complex electric field distribution inside the chamber). The calculations in this study demonstrate that even a small variation in simulated volume can lead to fairly large variations in the MC calculated ion chamber response in a magnetic field. This is an important effect that must be addressed to ensure proper calibration of MRgRT machines using MC ion chamber correction factors. This effect may play a role, even where there is no magnetic field, in small-field dosimetry when volume averaging effect are important.
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Affiliation(s)
- Victor N Malkov
- Department of Physics, Carleton Laboratory for Radiotherapy Physics, Carleton University, Ottawa, ON, Canada
| | - D W O Rogers
- Department of Physics, Carleton Laboratory for Radiotherapy Physics, Carleton University, Ottawa, ON, Canada
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25
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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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Hyun MA, Miller JR, Micka JA, DeWerd LA. Ion recombination and polarity corrections for small-volume ionization chambers in high-dose-rate, flattening-filter-free pulsed photon beams. Med Phys 2017; 44:618-627. [PMID: 28001291 DOI: 10.1002/mp.12053] [Citation(s) in RCA: 13] [Impact Index Per Article: 1.9] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/02/2016] [Revised: 10/25/2016] [Accepted: 11/16/2016] [Indexed: 11/06/2022] Open
Abstract
PURPOSE To investigate ion recombination and polarity effects in scanning and microionization chambers when used with digital electrometers and high-dose-rate linac beams such as flattening-filter-free (FFF) fields, and to compare results against conventional pulsed and continuous photon beams. METHODS Saturation curves were obtained for one Farmer-type ionization chamber and eight small-volume chamber models with volumes ranging from 0.01 to 0.13 cm3 using a Varian TrueBeam™ STx with FFF capability. Three beam modes (6 MV, 6 MV FFF, and 10 MV FFF) were investigated, with nominal dose-per-pulse values of 0.0278, 0.0648, and 0.111 cGy/pulse, respectively, at dmax . Saturation curves obtained using the Theratronics T1000 60 Co unit at the UWADCL and a conventional linear accelerator (Varian Clinac iX) were used to establish baseline behavior. Jaffé plots were fitted to obtain Pion , accounting for exponential effects such as charge multiplication. These values were compared with the two-voltage technique recommended in TG-51, and were plotted as a function of dose-per-pulse to assess the ability of small-volume chambers to meet reference-class criteria in FFF beams. RESULTS Jaffé- and two-voltage-determined Pion values measured for high-dose-rate beams agreed within 0.1% for the Farmer-type chamber and 1% for scanning and microionization chambers, with the exception of the CC01 which agreed within 2%. With respect to ion recombination and polarity effects, the Farmer-type chamber, scanning chambers and the Exradin A26 microchamber exhibited reference-class behavior in all beams investigated, with the exception of the IBA CC04 scanning chamber, which had an initial recombination correction that varied by 0.2% with polarity. All microchambers investigated, with the exception of the A26, exhibited anomalous polarity and ion recombination behaviors that make them unsuitable for reference dosimetry in conventional and high-dose-rate photon beams. CONCLUSIONS The results of this work demonstrate that recombination and polarity behaviors seen in conventional pulsed and continuous photon beams trend accordingly in high-dose-rate FFF linac beams. Several models of small-volume ionization chambers used with a digital electrometer have been shown to meet reference-class requirements with respect to ion recombination and polarity, even in the high-dose-rate environment. For such chambers, a two-voltage technique agreed well with more rigorous methods of determining Pion . However, the results emphasize the need for careful reference detector selection, and indicate that ionization chambers ought to be extensively tested in each beam of interest prior to their use for reference dosimetry.
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Affiliation(s)
- Megan A Hyun
- Department of Medical Physics, School of Medicine and Public Health, University of Wisconsin-Madison, Madison, WI, 53705, USA
| | - Jessica R Miller
- Department of Human Oncology, School of Medicine and Public Health, University of Wisconsin-Madison, Madison, WI, 53792, USA
| | - John A Micka
- Department of Medical Physics, School of Medicine and Public Health, University of Wisconsin-Madison, Madison, WI, 53705, USA
| | - Larry A DeWerd
- Department of Medical Physics, School of Medicine and Public Health, University of Wisconsin-Madison, Madison, WI, 53705, USA
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28
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Dowdell S, Tyler M, McNamara J, Sloan K, Ceylan A, Rinks A. Potential errors in relative dose measurements in kilovoltage photon beams due to polarity effects in plane-parallel ionisation chambers. Phys Med Biol 2016; 61:8395-8407. [DOI: 10.1088/0031-9155/61/23/8395] [Citation(s) in RCA: 5] [Impact Index Per Article: 0.6] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/12/2022]
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29
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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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30
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Muir BR. Ion chamber absorbed dose calibration coefficients, N(D,w), measured at ADCLs: distribution analysis and stability. Med Phys 2015; 42:1546-54. [PMID: 25832045 DOI: 10.1118/1.4914381] [Citation(s) in RCA: 10] [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 To analyze absorbed dose calibration coefficients, ND,w, measured at accredited dosimetry calibration laboratories (ADCLs) for client ionization chambers to study (i) variability among ND,w coefficients for chambers of the same type calibrated at each ADCL to investigate ion chamber volume fluctuations and chamber manufacturing tolerances; (ii) equivalency of ion chamber calibration coefficients measured at different ADCLs by intercomparing ND,w coefficients for chambers of the same type; and (iii) the long-term stability of ND,w coefficients for different chamber types by investigating repeated chamber calibrations. METHODS Large samples of ND,w coefficients for several chamber types measured over the time period between 1998 and 2014 were obtained from the three ADCLs operating in the United States. These are analyzed using various graphical and numerical statistical tests for the four chamber types with the largest samples of calibration coefficients to investigate (i) and (ii) above. Ratios of calibration coefficients for the same chamber, typically obtained two years apart, are calculated to investigate (iii) above and chambers with standard deviations of old/new ratios less than 0.3% meet stability requirements for accurate reference dosimetry recommended in dosimetry protocols. RESULTS It is found that ND,w coefficients for a given chamber type compared among different ADCLs may arise from differing probability distributions potentially due to slight differences in calibration procedures and/or the transfer of the primary standard. However, average ND,w coefficients from different ADCLs for given chamber types are very close with percent differences generally less than 0.2% for Farmer-type chambers and are well within reported uncertainties. CONCLUSIONS The close agreement among calibrations performed at different ADCLs reaffirms the Calibration Laboratory Accreditation Subcommittee process of ensuring ADCL conformance with National Institute of Standards and Technology standards. This study shows that ND,w coefficients measured at different ADCLs are statistically equivalent, especially considering reasonable uncertainties. This analysis of ND,w coefficients also allows identification of chamber types that can be considered stable enough for accurate reference dosimetry.
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Affiliation(s)
- B R Muir
- Measurement Science and Standards, National Research Council of Canada, 1200 Montreal Road, Ottawa, Ontario K1A 0R6, Canada
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31
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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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32
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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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33
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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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McEwen M, DeWerd L, Ibbott G, Followill D, Rogers DWO, Seltzer S, Seuntjens J. Addendum to the AAPM's TG-51 protocol for clinical reference dosimetry of high-energy photon beams. Med Phys 2014; 41:041501. [PMID: 24694120 PMCID: PMC5148035 DOI: 10.1118/1.4866223] [Citation(s) in RCA: 201] [Impact Index Per Article: 20.1] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/03/2013] [Revised: 02/03/2014] [Accepted: 02/06/2014] [Indexed: 11/07/2022] Open
Abstract
An addendum to the AAPM's TG-51 protocol for the determination of absorbed dose to water in megavoltage photon beams is presented. This addendum continues the procedure laid out in TG-51 but new kQ data for photon beams, based on Monte Carlo simulations, are presented and recommendations are given to improve the accuracy and consistency of the protocol's implementation. The components of the uncertainty budget in determining absorbed dose to water at the reference point are introduced and the magnitude of each component discussed. Finally, the consistency of experimental determination of ND,w coefficients is discussed. It is expected that the implementation of this addendum will be straightforward, assuming that the user is already familiar with TG-51. The changes introduced by this report are generally minor, although new recommendations could result in procedural changes for individual users. It is expected that the effort on the medical physicist's part to implement this addendum will not be significant and could be done as part of the annual linac calibration.
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Affiliation(s)
- Malcolm McEwen
- National Research Council, 1200 Montreal Road, Ottawa, Ontario, Canada
| | - Larry DeWerd
- University of Wisconsin, 1111 Highland Avenue, Madison, Wisconsin 53705
| | - Geoffrey Ibbott
- Department of Radiation Physics, M D Anderson Cancer Center, 1515 Holcombe Boulevard, Houston, Texas 77030
| | - David Followill
- IROC Houston QA Center, Radiological Physics Center, 8060 El Rio Street, Houston, Texas 77054
| | - David W O Rogers
- Carleton Laboratory for Radiotherapy Physics, Physics Department, Carleton University, 1125 Colonel By Drive, Ottawa, Ontario, Canada
| | - Stephen Seltzer
- National Institute of Standards and Technology, Gaithersburg, Maryland 20899
| | - Jan Seuntjens
- Medical Physics Unit, McGill University, 1650 Cedar Avenue, Montreal, Québec, Canada
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Vahabi SM, Shamsaie Zafarghandi M, Ghasemi M, Alipoor A, Shahvar A. A prototype of an ionization chamber for gamma radiation beams of 60Co: Experimental and Monte Carlo preliminary results. RADIAT MEAS 2013. [DOI: 10.1016/j.radmeas.2013.09.004] [Citation(s) in RCA: 5] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/26/2022]
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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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Ali ESM, McEwen MR, Rogers DWO. Detailed high-accuracy megavoltage transmission measurements: a sensitive experimental benchmark of EGSnrc. Med Phys 2012; 39:5990-6003. [PMID: 23039637 DOI: 10.1118/1.4745561] [Citation(s) in RCA: 6] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/07/2022] Open
Abstract
PURPOSE There are three goals for this study: (a) to perform detailed megavoltage transmission measurements in order to identify the factors that affect the measurement accuracy, (b) to use the measured data as a benchmark for the EGSnrc system in order to identify the computational limiting factors, and (c) to provide data for others to benchmark Monte Carlo codes. METHODS Transmission measurements are performed at the National Research Council Canada on a research linac whose incident electron parameters are independently known. Automated transmission measurements are made on-axis, down to a transmission value of ∼1.7%, for eight beams between 10 MV (the lowest stable MV beam on the linac) and 30 MV, using fully stopping Be, Al, and Pb bremsstrahlung targets and no fattening filters. To diversify energy differentiation, data are acquired for each beam using low-Z and high-Z attenuators (C and Pb) and Farmer chambers with low-Z and high-Z buildup caps. Experimental corrections are applied for beam drifts (2%), polarity (2.5% typical maximum, 6% extreme), ion recombination (0.2%), leakage (0.3%), and room scatter (0.8%)-the values in parentheses are the largest corrections applied. The experimental setup and the detectors are modeled using EGSnrc, with the newly added photonuclear attenuation included (up to a 5.6% effect). A detailed sensitivity analysis is carried out for the measured and calculated transmission data. RESULTS The developed experimental protocol allows for transmission measurements with 0.4% uncertainty on the smallest signals. Suggestions for accurate transmission measurements are provided. Measurements and EGSnrc calculations agree typically within 0.2% for the sensitivity of the transmission values to the detector details, to the bremsstrahlung target material, and to the incident electron energy. Direct comparison of the measured and calculated transmission data shows agreement better than 2% for C (3.4% for the 10 MV beam) and typically better than 1% for Pb. The differences can be explained by acceptable photon cross section changes of ≤0.4%. CONCLUSIONS Accurate transmission measurements require accounting for a number of influence quantities which, if ignored, can collectively introduce errors larger than 10%. Accurate transmission calculations require the use of the most accurate data and physics options available in EGSnrc, particularly the more accurate bremsstrahlung angular sampling option and the newly added modeling of photonuclear attenuation. Comparison between measurements and calculations implies that EGSnrc is accurate within 0.2% for relative ion chamber response calculations. Photon cross section uncertainties are the ultimate limiting factor for the accuracy of the calculated transmission data (Monte Carlo or analytical).
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Affiliation(s)
- E S M Ali
- Department of Physics, Carleton University, Ottawa, Ontario, Canada.
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