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Rogers DWO. Minimum phantom size for megavoltage photon beam reference dosimetry. Med Phys 2024; 51:5663-5671. [PMID: 38669481 DOI: 10.1002/mp.17099] [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: 12/14/2023] [Revised: 04/07/2024] [Accepted: 04/08/2024] [Indexed: 04/28/2024] Open
Abstract
BACKGROUND Water phantoms are required to perform reference dosimetry and beam quality measurements but there are no published studies about the size requirements for such phantoms. PURPOSE To investigate, using Monte Carlo techniques, the size requirements for water phantoms used in reference dosimetry and/or to measure the beam quality specifiers% d d ( 10 ) x $\%dd(10)_{\sf x}$ andT P R 10 20 $TPR^{20}_{10}$ . METHODS The EGSnrc application DOSXYZnrc is used to calculateD ( 10 ) $D(10)$ , the dose per incident fluence at 10 cm depth in a water phantom irradiated by incident10 × 10 cm 2 $10\,\times \,10 \, {\rm {cm}}^{2}$ beams of60 Co $^{60}{\rm {Co}}$ or 6 MV photons. The water phantom dimensions are varied from30 × 30 × 40 cm 3 $30 \,\times \, 30 \,\times \, 40 \, {\rm {cm}}^3$ to15 × 15 × 22 cm 3 $15 \,\times \, 15 \,\times \, 22 \, {\rm {cm}}^3$ and occasionally smaller. The% d d ( 10 ) x $\%dd(10)_{\sf x}$ andT P R 10 20 $TPR^{20}_{10}$ values are also calculated with care being taken to distinguishT P R 10 20 $TPR^{20}_{10}$ results when using Method A (changing depth of water in phantom) and Method B (moving entire phantom). Typical statistical uncertainties are 0.03%. RESULTS Phantom dimensions have only minor effects for phantoms larger than20 × 20 × 25 cm 3 $20 \,\times \, 20 \,\times \, 25 \, {\rm {cm}}^3$ . A table of corrections to the dose at 10 cm depth in10 × 10 cm 2 $10 \,\times \, 10 \, {\rm {cm}}^{2}$ beams of60 Co $^{60}{\rm {Co}}$ or 6 MV photons are provided and range from no correction to 0.75% for a60 Co $^{60}{\rm {Co}}$ beam incident on a20 × 20 × 15 cm 3 $20 \,\times \, 20 \,\times \, 15 \, {\rm {cm}}^3$ phantom. There can be distinct differences in theT P R 10 20 $TPR^{20}_{10}$ values measured using Method A or Method B, especially for smaller phantoms. It is explicitly demonstrated that, within ± $\pm$ 0.15%,T P R 10 20 $TPR^{20}_{10}$ values for a30 × 30 × 30 cm 3 $30 \,\times \, 30 \,\times \, 30 \, {\rm {cm}}^3$ phantom measured using Method A or B are independent of source detector distance between 40 and 200 cm. CONCLUSIONS The phantom sizes recommended in the TG-51 and IAEA TRS-398 reference dosimetry protocols are adequate for accurate reference dosimetry and in some cases are even conservative. Correction factors are necessary for accurate measurement of the dose at 10 cm depth in smaller phantoms and these factors are provided. Very accurate beam quality specifiers are not required for reference dosimetry itself, but for specifying beam stability and characteristics it is important to specify phantom sizes and also the method used forT P R 10 20 $TPR^{20}_{10}$ measurements.
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Affiliation(s)
- D W O Rogers
- Carleton Laboratory for Radiotherapy Physics, Department of Physics, Carleton University, Ottawa, Canada
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Failing T, Hensley FW, Keil B, Zink K. Investigations on the beam quality correction factor for ionization chambers in high-energy brachytherapy dosimetry. Phys Med Biol 2024; 69:165002. [PMID: 39009012 DOI: 10.1088/1361-6560/ad638b] [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: 11/30/2023] [Accepted: 07/15/2024] [Indexed: 07/17/2024]
Abstract
Objective. To enhance the investigations on MC calculated beam quality correction factors of thimble ionization chambers from high-energy brachytherapy sources and to develop reliable reference conditions in source and detector setups in water.Approach. The response of five different ionization chambers from PTW-Freiburg and Standard Imaging was investigated for irradiation by a high dose rate Ir-192 Flexisource in water. For a setup in a Beamscan water phantom, Monte Carlo simulations were performed to calculate correction factors for the chamber readings. After exact positioning of source and detector the absorbed dose rate at the TG-43 reference point at one centimeter nominal distance from the source was measured using these factors and compared to the specification of the calibration certificate. The Monte Carlo calculations were performed using the restricted cema formalism to gain further insight into the chamber response. Calculations were performed for the sensitive volume of the chambers, determined by the methods currently used in investigations of dosimetry in magnetic fields.Main results. Measured dose rates and values from the calibration certificate agreed within the combined uncertainty (k= 2) for all chambers except for one case in which the full air cavity was simulated. The chambers showed a distinct directional dependence. With the restricted cema formalism calculations it was possible to examine volume averaging and energy dependence of the perturbation factors contributing to the beam quality correction factor also differential in energy.Significance. This work determined beam quality correction factors to measure the absorbed dose rate from a brachytherapy source in terms of absorbed dose to water for a variety of ionization chambers. For the accurate dosimetry of brachytherapy sources with ionization chambers it is advisable to use correction factors based on the sensitive volume of the chambers and to take account for the directional dependence of chamber response.
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Affiliation(s)
- T Failing
- Institute of Medical Physics and Radiation Protection (IMPS), University of Applied Sciences, Gießen, Germany
| | - F W Hensley
- Department for Radiotherapy and Radiooncology, University Medical Center Heidelberg, Heidelberg, Germany
| | - B Keil
- Institute of Medical Physics and Radiation Protection (IMPS), University of Applied Sciences, Gießen, Germany
- Department for Diagnostic and Interventional Radiology, Philipps-University Marburg, Marburg, Germany
- LOEWE Research Cluster for Advanced Medical Physics in Imaging and Therapy (ADMIT), TH Mittelhessen University of Applied Sciences, Giessen, Germany
| | - K Zink
- Institute of Medical Physics and Radiation Protection (IMPS), University of Applied Sciences, Gießen, Germany
- LOEWE Research Cluster for Advanced Medical Physics in Imaging and Therapy (ADMIT), TH Mittelhessen University of Applied Sciences, Giessen, Germany
- Department for Radiotherapy and Radiooncology, University Medical Center Giessen-Marburg, Marburg, Germany
- Marburg Iontherapy Center (MIT), Marburg, Germany
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Yip E, Tari SY, Reynolds MW, Sinn D, Murray BR, Fallone BG, Oliver PA. Clinical reference dosimetry for the 0.5 T inline rotating biplanar Linac-MR. Med Phys 2024; 51:2933-2940. [PMID: 38308821 DOI: 10.1002/mp.16951] [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: 08/09/2023] [Revised: 11/13/2023] [Accepted: 12/26/2023] [Indexed: 02/05/2024] Open
Abstract
BACKGROUND The world's first clinical 0.5 T inline rotating biplanar Linac-MR system is commissioned for clinical use. For reference dosimetry, unique features to device, including an SAD = 120 cm, bore clearance of 60 cm × 110 cm, as well as 0.5 T inline magnetic field, provide some challenges to applying a standard dosimetry protocol (i.e., TG-51). PURPOSE In this work, we propose a simple and practical clinical reference dosimetry protocol for the 0.5T biplanar Linac-MR and validated its results. METHODS Our dosimetry protocol for this system is as follows: tissue phantom ratios at 20 and 10 cm are first measured and converted into %dd10x beam quality specifier using equations provided and Kalach and Rogers. The converted %dd10x is used to determine the ion chamber correction factor, using the equations in the TG-51 addendum for the Exradin A12 farmer chamber used, which is cross-calibrated with one calibrated at a standards laboratory. For a 0.5 T parallel field, magnetic field effect on chamber response is assumed to have no effect and is not explicitly corrected for. Once the ion chamber correction factor for a non-standard SAD (kQ,msr) is determined, TG-51 is performed to obtain dose at a depth of 10 cm at SAD = 120 cm. The dosimetry protocol is repeated with the magnetic field ramped down. To validate our dosimetry protocol, Monte Carlo (EGSnrc) simulations are performed to confirm the determined kQ,msr values. MC Simulations and magnetic Field On versus Field Off measurements are performed to confirm that the magnetic field has no effect. To validate our overall dosimetry protocol, external dose audits, based on optical simulated luminescent dosimeters, thermal luminescent dosimeters, and alanine dosimeters are performed on the 0.5 T Linac-MR system. RESULTS Our EGSnrc results confirm our protocol-determined kQ,msr values, as well as our assumptions about magnetic field effects (kB = 1) within statistical uncertainty for the A-12 chamber. Our external dosimetry procedures also validated our overall dosimetry protocol for the 0.5 T biplanar Linac-MR hybrid. Ramping down the magnetic field has resulted in a dosimetric difference of 0.1%, well within experimental uncertainty. CONCLUSION With the 0.5 T parallel magnetic field having minimal effect on the ion chamber response, a TPR20,10 approach to determine beam quality provides an accurate method to perform clinical dosimetry for the 0.5 T biplanar Linac-MR.
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Affiliation(s)
- Eugene Yip
- Department of Oncology, Medical Physics Division, University of Alberta, Edmonton, Alberta, Canada
- Department of Medical Physics, Cross Cancer Institute, Edmonton, Alberta, Canada
| | - Shima Y Tari
- Department of Oncology, Medical Physics Division, University of Alberta, Edmonton, Alberta, Canada
- Department of Medical Physics, Cross Cancer Institute, Edmonton, Alberta, Canada
| | - Michael W Reynolds
- Department of Medical Physics, Cross Cancer Institute, Edmonton, Alberta, Canada
- Department of Radiation Oncology, BC Cancer - Victoria, Victoria, British Columbia, Canada
| | - David Sinn
- Department of Medical Physics, Cross Cancer Institute, Edmonton, Alberta, Canada
- Department of Radiaiton Oncology, The Queen's Medical Centre, Honolulu, Hawaii, USA
| | - Brad R Murray
- MagnetTx Oncology Solutions, Edmonton, Alberta, Canada
| | - B Gino Fallone
- Department of Oncology, Medical Physics Division, University of Alberta, Edmonton, Alberta, Canada
- Department of Medical Physics, Cross Cancer Institute, Edmonton, Alberta, Canada
- MagnetTx Oncology Solutions, Edmonton, Alberta, Canada
| | - Patricia Ak Oliver
- Department of Oncology, Medical Physics Division, University of Alberta, Edmonton, Alberta, Canada
- Department of Medical Physics, Cross Cancer Institute, Edmonton, Alberta, Canada
- Department of Medical Physics, Nova Scotia Health, Halifax, Nova Scotia, Canada
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4
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Mahfirotin DA, Ferliano B, Handika AD, Asril YS, Fadli M, Ryangga D, Nelly N, Kurniawan E, Wibowo WE, Yadav P, Pawiro SA. A multicenter study of modified electron beam output calibration. J Appl Clin Med Phys 2024; 25:e14232. [PMID: 38088260 PMCID: PMC10795448 DOI: 10.1002/acm2.14232] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/28/2023] [Revised: 11/13/2023] [Accepted: 11/19/2023] [Indexed: 01/19/2024] Open
Abstract
PURPOSE This study aims to assess the accuracy of a modified electron beam calibration based on the IAEA TRS-398 and AAPM-TG-51 in multicenter radiotherapy. METHODS This study was performed using the Elekta and Varian Linear Accelerator electron beams with energies of 4-22 MeV under reference conditions using cylindrical (PTW 30013, IBA FC65-G, and IBA FC65-P) and parallel-plate (PTW 34045, PTW 34001, and IBA PPC-40) chambers. The modified calibration used a cylindrical chamber and an updatedk ' Q $k{^{\prime}}_Q$ based on Monte Carlo calculations, whereas TRS-398 and TG-51 used cylindrical and parallel-plate chambers for reference dosimetry. The dose ratio of the modified calibration procedure, TRS-398 and TG-51 were obtained by comparing the dose at the maximum depth of the modified calibration to TRS-398 and TG-51. RESULTS The study found that all cylindrical chambers' beam quality conversion factors determined with the modified calibration( k ' Q ) $( {{{k^{\prime}}}_Q} )$ to the TRS-398 and TG-51 vary from 0.994 to 1.003 and 1.000 to 1.010, respectively. The dose ratio of modified/TRS-398cyl and modified/TRS-398parallel-plate, the variation ranges were 0.980-1.014 and 0.981-1.019, while for the counterpart modified/TG-51cyl was found varying between 0.991 and 1.017 and the ratio of modified/TG-51parallel-plate varied in the range of 0.981-1.019. CONCLUSION This multi-institutional study analyzed a modified calibration procedure utilizing new data for electron beam calibrations at multiple institutions and evaluated existing calibration protocols. Based on observed variations, the current calibration protocols should be updated with detailed metrics on the stability of linac components.
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Affiliation(s)
- Dwi Aprilia Mahfirotin
- Department of PhysicsFaculty of Mathematics and Natural SciencesUniversitas Indonesia, DepokWest JavaIndonesia
- Department of Radiation OncologyMitra Keluarga Bekasi Timur Hospital, BekasiWest JavaIndonesia
| | - Brian Ferliano
- Department of Radiation OncologyGading Pluit HospitalJakartaIndonesia
| | - Andrian Dede Handika
- Department of Radiation OncologyPersahabatan Central General HospitalJakartaIndonesia
| | - Yosi Sudarsi Asril
- Department of Radiation OncologyMayapada Hospital Jakarta SelatanJakartaIndonesia
| | - Muhamad Fadli
- Department of Radiation OncologyMRCCC Siloam Hospital SemanggiJakartaIndonesia
| | - Dea Ryangga
- Department of Radiation OncologyPasar Minggu Regional HospitalJakartaIndonesia
| | - Nelly Nelly
- Department of Radiation OncologySiloam Hospital TB SimatupangJakartaIndonesia
| | - Eddy Kurniawan
- Department of Radiation OncologyTzu Chi HospitalJakartaIndonesia
| | - Wahyu Edy Wibowo
- Department of Radiation OncologyDr. Cipto Mangunkusumo National General Hospital CentralFaculty of MedicineUniversitas IndonesiaJakartaIndonesia
| | - Poonam Yadav
- Department of Radiation OncologyNorthwestern Memorial HospitalNorthwestern University Feinberg School of MedicineChicagoIllinoisUSA
| | - Supriyanto Ardjo Pawiro
- Department of PhysicsFaculty of Mathematics and Natural SciencesUniversitas Indonesia, DepokWest JavaIndonesia
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Yulinar C, Assegab MI, Wibowo WE, Pawiro SA. Modified calibration protocols in electron beam dosimetry: comparison with IAEA TRS-398 and AAPM TG-51. Biomed Phys Eng Express 2023; 9:055008. [PMID: 37442101 DOI: 10.1088/2057-1976/ace722] [Citation(s) in RCA: 1] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/11/2023] [Accepted: 07/13/2023] [Indexed: 07/15/2023]
Abstract
This study aimed to compare absolute calibration outputs based on the protocols of the International Atomic Energy Agency (IAEA) Technical Report Series (TRS)-398, the American Association of Physicists in Medicine (AAPM) Task Group (TG)-51, and modified calibration approach. The electron beam output calibration followed the IAEA TRS-398 and AAPM TG-51 protocols, both of which required cylindrical chambers and parallel plates. However, the use of cylindrical chambers is not recommended at low energies because of the large fluence-correction factor. TG-51 recommended cross-calibration of the parallel-plate chamber against the cylindrical chamber in a high-energy electron beam. In 2020, an electron beam dosimetry modification was introduced that used a cylindrical ionisation chamber at all energies and updated the data for beam quality conversion factors. This modification provided a lower deviation than that reported in AAPM TG-51. Thus, the modified calibration based on TRS-398 was applied in the present study, which yielded results below the permissible tolerance. The beam calibration at 6, 8, 10, 12, and 15 MeV energies was carried out for two Elekta linear accelerators.. Electron beam dosimetry followed the AAPM TG-51 and TRS-398 protocols, and modified calibration were performed to measure the dose at the maximum depth expressed in dose/monitor units (cGy/MU). Charge-reading measurements were measured using ionisation chambers PTW 30013, IBA CC13, and Exradin A11. The average absorbed dose ratios were 1.004 and 1.009 using the modified calibration and TRS-398 and modified calibration and TG-51, respectively. Therefore, based on IAEA TRS-398, the results were below the tolerance limit (±2%).
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Affiliation(s)
- Cica Yulinar
- Department of Physics, Faculty of Mathematics and Natural Sciences, Universitas Indonesia, Depok, Indonesia
- Department of Radiation Oncology, Tzu Chi Hospital, Jakarta, 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
| | - Supriyanto Ardjo Pawiro
- Department of Physics, Faculty of Mathematics and Natural Sciences, Universitas Indonesia, Depok, Indonesia
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Sushma N, Kaginelli S, Sathiyaraj P, Senthil Manikandan P, Ganesh KM. Analysis of fetal dose using Optically Simulated Luminescence Dosimeter and ion chamber in randophantom for various radiotherapy techniques. Appl Radiat Isot 2023; 198:110854. [PMID: 37209491 DOI: 10.1016/j.apradiso.2023.110854] [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: 01/02/2023] [Revised: 05/08/2023] [Accepted: 05/11/2023] [Indexed: 05/22/2023]
Abstract
To analyse the fetal dose in all three trimesters in patients treated for brain tumors during pregnancy, a modified rando phantom representing three different trimesters was used with provisions for insertion of ion-chamber and Optically Simulated Luminescence Dosimeter (OSLD). The measurement regions were chosen at the level of fundus, umbilicus and pubis. Seven different treatment plans with 6FF and 6FFF beam energies were generated. Treating pregnant patients with brain tumors is safe irrespective of planning modalities except 3DCRT plan where the dose is 10.24 cGy.
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Affiliation(s)
- N Sushma
- Department of Radiation Physics, Kidwai Memorial Institute of Oncology, Bengaluru, India; Division of Medical Physics, JSS Academy of Higher Education and Research, Mysuru, India
| | - Shanmukhappa Kaginelli
- Division of Medical Physics, JSS Academy of Higher Education and Research, Mysuru, India
| | - P Sathiyaraj
- Department of Radiation Physics, Kidwai Memorial Institute of Oncology, Bengaluru, India
| | - P Senthil Manikandan
- Department of Radiation Physics, Kidwai Memorial Institute of Oncology, Bengaluru, India
| | - K M Ganesh
- Department of Radiation Physics, Kidwai Memorial Institute of Oncology, Bengaluru, India.
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Hosseini Bojdani SM, Baghani HR, Robatjazi M, Andreoli S, Azadegan B. Comparison of derived correction factors for effects of ion recombination and photon beam quality index following TG-51 and TRS-398 dosimetry protocols. Appl Radiat Isot 2023; 197:110796. [PMID: 37037135 DOI: 10.1016/j.apradiso.2023.110796] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/14/2022] [Revised: 03/07/2023] [Accepted: 03/28/2023] [Indexed: 04/12/2023]
Abstract
In this study, ion recombination correction factor (kS) and beam quality conversion factor ( [Formula: see text] ) values were extracted following the recommendations of the TRS-398 and TG-51 dosimetry protocols for widely used cylindrical ionization chambers for high energy photon beam dosimetry to quantify the agreement between the instructions for these two protocols for absolute dosimetry inside water. Four different types of cylindrical ionization chambers comprising Farmer (TM30013), Semiflex 0.125 cm3 (TM31010), Semiflex 0.3 cm3 (TM31013), and PinPoint (TM31016) were considered, and kS and [Formula: see text] values were determined at photon energies of 6 MV and 15 MV. The maximum difference between the measured kS values according to the instructions in the TRS-398 and TG-51 protocols was 0.03%. The kS data measured with both protocols agreed well with those measured by using the Jaffe-plot approach, where the maximum difference was about 0.33%. The observed differences between the [Formula: see text] factors measured by using the TRS-398 and TG-51 dosimetry protocols at photon energies of 6 MV and 15 MV were 0.37% and 0.55%, respectively. The [Formula: see text] values measured using the TG-51 dosimetry protocols were slightly closer to those measured by a reference ionization chamber dosimeter. We conclude that the maximum differences were about 0.4% and 0.6% in the absorbed dose measurements according to the TRS-398 and TG-51 instructions at photon energies of 6 MV and 15 MV, respectively. The type of ionization chamber employed also affected the differences, where the maximum and minimum dose differences were found using the Farmer and PinPoint chambers, respectively.
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Affiliation(s)
| | | | - Mostafa Robatjazi
- Medical Physics and Radiological Sciences Department, Sabzevar University of Medical Sciences, Sabzevar, Iran
| | | | - Behnam Azadegan
- Physics Department, Hakim Sabzevari University, Sabzevar, Iran
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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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Szpala S, Renaud J, Muir BR, Bourgouin A, Kohli K, McEwen M. Calorimeter measurements of absolute dose in aluminum, a surrogate of bone, to validate dose-to-medium in Acuros XB. Phys Med Biol 2022; 68. [PMID: 36579808 DOI: 10.1088/1361-6560/aca869] [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: 05/19/2022] [Accepted: 12/02/2022] [Indexed: 12/30/2022]
Abstract
Objective. While the accuracy of dose calculations in water with Acuros XB is well established, experimental validation of dose in bone is limited. Acuros XB reports both dose-to-medium and dose-to-water, and these values differ in bone, but there are no reports of measurements of validation in bone. This work compares Acuros XB calculations to measurements of absolute dose in aluminum (medium similar to bone). The validity of using selected relative dosimeters in aluminum is also investigated.Approach. A calorimeter with an aluminum core embedded in an aluminum phantom was selected as bone surrogate for the measurement of absolute dose. Matching the medium of the core to the medium of the phantom allowed eliminating the calculation of the conversion between media. The dose was measured at the fixed depth of 3.3 cm in aluminum (∼9 g·cm-2) with 6X, 10X, 6FFF and 10FFF photon beams from a TrueBeam Varian linac. In addition, experimental cross-calibration between water and aluminum was performed for an IBA CC13 ionization chamber, a PTW microDiamond and EBT3 Gafchromic film.Main results. Calculations with Acuros XB dose-to-medium in aluminum differed from the calorimetry data by -2.8% to -3.5%, depending on the beam. Use of dose-to-water would have resulted in about 39% discrepancy. The cross calibration coefficient between water and aluminum yielded values of about 0.87 for the CC13 chamber, 0.91 for the microDiamond, and 0.88 for the film, and independent of the beam within about ±1%.Significance. It was demonstrated the value of the dose-to-medium in aluminum (surrogate of bone) computed with Acuros XB is close to the value of the absolute dose measured with a calorimeter, and there is a significant discrepancy when dose-to-water is used instead. The use of an ionization chamber, a microDiamond and Gafchromic film in aluminum required a considerable correction from calibration in water.
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Affiliation(s)
| | - James Renaud
- Metrology Research Centre, National Research Council of Canada, Ottawa, Ontario, Canada
| | - Bryan R Muir
- Metrology Research Centre, National Research Council of Canada, Ottawa, Ontario, Canada
| | - Alexandra Bourgouin
- Dosimetry for Radiation Therapy and Diagnostic Radiology, Physikalisch-Technische Bundesanstalt (PTB), Braunschweig, Lower Saxony, D-38116, Germany
| | | | - Malcolm McEwen
- Metrology Research Centre, National Research Council of Canada, Ottawa, Ontario, Canada
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Walter AE, DeWerd LA. Feasibility of implementing a megavoltage ionization chamber calibration service at the secondary standards level. Radiat Phys Chem Oxf Engl 1993 2022. [DOI: 10.1016/j.radphyschem.2022.110699] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/05/2022]
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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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12
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Duchaine J, Markel D, Bouchard H. A probabilistic approach for determining Monte Carlo beam source parameters: I. Modeling of a CyberKnife M6 unit. Phys Med Biol 2022; 67. [DOI: 10.1088/1361-6560/ac4ef7] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/04/2021] [Accepted: 01/26/2022] [Indexed: 11/12/2022]
Abstract
Abstract
Objective. During Monte Carlo modeling of external radiotherapy beams, models must be adjusted to reproduce the experimental measurements of the linear accelerator being considered. The aim of this work is to propose a new method for the determination of the energy and spot size of the electron beam incident on the target of a linear accelerator using a maximum likelihood estimation. Approach. For that purpose, the method introduced by Francescon et al (2008 Med. Phys.
35 504–13) is expanded upon in this work. Simulated tissue-phantom ratios and uncorrected output factors using a set of different detector models are compared to experimental measurements. A probabilistic formalism is developed and a complete uncertainty budget, which includes a detailed simulation of positioning errors, is evaluated. The method is applied to a CyberKnife M6 unit using four detectors (PTW 60012, PTW 60019, Exradin A1SL and IBA CC04), with simulations being performed using the EGSnrc suite. Main results. The likelihood distributions of the electron beam energy and spot size are evaluated, leading to
E
ˆ
=
7.42
±
0.17
MeV
and
F
ˆ
=
2.15
±
0.06
mm
. Using these results and a 95% confidence region, simulations reproduce measurements in 13 out of the 14 considered setups. Significance. The proposed method allows an accurate beam parameter optimization and uncertainty evaluation during the Monte Carlo modeling of a radiotherapy unit.
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13
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Alissa M, Zink K, Tessier F, Schoenfeld AA, Czarnecki D. Monte Carlo calculated beam quality correction factors for two cylindrical ionization chambers in photon beams. Phys Med 2021; 94:17-23. [PMID: 34972070 DOI: 10.1016/j.ejmp.2021.12.012] [Citation(s) in RCA: 5] [Impact Index Per Article: 1.7] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 05/19/2021] [Revised: 10/04/2021] [Accepted: 12/19/2021] [Indexed: 11/20/2022] Open
Abstract
PURPOSE Although several studies provide data for reference dosimetry, the SNC600c and SNC125c ionization chambers (Sun Nuclear Corporation, Melbourne, FL) are in clinical use worldwide for which no beam quality correction factors kQ are available. The goal of this study was to calculate beam quality correction factors kQ for these ionization chambers according to dosimetry protocols TG-51, TRS 398 and DIN 6800-2. METHODS Monte Carlo simulations using EGSnrc have been performed to calculate the absorbed dose to water and the dose to air within the active volume of ionization chamber models. Both spectra and simulations of beam transport through linear accelerator head models were used as radiation sources for the Monte Carlo calculations. RESULTS kQ values as a function of the respective beam quality specifier Q were fitted against recommended equations for photon beam dosimetry in the range of 4 MV to 25 MV. The fitting curves through the calculated values showed a root mean square deviation between 0.0010 and 0.0017. CONCLUSIONS The investigated ionization chamber models (SNC600c, SNC125c) are not included in above mentioned dosimetry protocols, but are in clinical use worldwide. This study covered this knowledge gap and compared the calculated results with published kQ values for similar ionization chambers. Agreements with published data were observed in the 95% confidence interval, confirming the use of data for similar ionization chambers, when there are no kQ values available for a given ionization chamber.
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Affiliation(s)
- Mohamad Alissa
- Institute of Medical Physics and Radiation Protection, University of Applied Sciences Giessen (THM), Giessen, Germany.
| | - Klemens Zink
- Institute of Medical Physics and Radiation Protection, University of Applied Sciences Giessen (THM), Giessen, Germany; Department of Radiotherapy and Radiation Oncology, University Medical Center Giessen and Marburg, Marburg, Germany; Marburg Ionbeam Therapycenter (MIT), Marburg, Germany
| | - Frédéric Tessier
- Ionization Radiation Standards, National Research Council, Ottawa, Canada
| | | | - Damian Czarnecki
- Institute of Medical Physics and Radiation Protection, University of Applied Sciences Giessen (THM), Giessen, Germany
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14
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Cervantes Y, Duchaine J, Billas I, Duane S, Bouchard H. Monte Carlo calculation of detector perturbation and quality correction factors in a 1.5 T magnetic resonance guided radiation therapy small photon beams. Phys Med Biol 2021; 66. [PMID: 34700311 DOI: 10.1088/1361-6560/ac3344] [Citation(s) in RCA: 4] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/27/2021] [Accepted: 10/26/2021] [Indexed: 01/02/2023]
Abstract
Objective.With future advances in magnetic resonance imaging-guided radiation therapy, small photon beams are expected to be included regularly in clinical treatments. This study provides physical insights on detector dose-response to multiple megavoltage photon beam sizes coupled to magnetic fields and determines optimal orientations for measurements.Approach.Monte Carlo simulations determine small-cavity detector (solid-state: PTW60012 and PTW60019, ionization chambers: PTW31010, PTW31021, and PTW31022) dose-responses in water to an Elekta Unity 7 MV FFF photon beam. Investigations are performed for field widths between 0.25 and 10 cm in four detector axis orientations with respect to the 1.5 T magnetic field and the photon beam. The magnetic field effect on the overall perturbation factor (PMC) accounting for the extracameral components, atomic composition, and density is quantified in each orientation. The density (Pρ) and volume averaging (Pvol) perturbation factors and quality correction factors (kQB,QfB,f) accounting for the magnetic field are also calculated in each orientation.Main results.Results show thatPvolremains the most significant perturbation both with and without magnetic fields. In most cases, the magnetic field effect onPvolis 1% or less. The magnetic field effect onPρis more significant on ionization chambers than on solid-state detectors. This effect increases up to 1.564 ± 0.001 with decreasing field size for chambers. On the contrary, the magnetic field effect on the extracameral perturbation factor is higher on solid-state detectors than on ionization chambers. For chambers, the magnetic field effect onPMCis only significant for field widths <1 cm, while, for solid-state detectors, this effect exhibits different trends with orientation, indicating that the beam incident angle and geometry play a crucial role.Significance.Solid-state detectors' dose-response is strongly affected by the magnetic field in all orientations. The magnetic field impact on ionization chamber response increases with decreasing field size. In general, ionization chambers yieldkQB,QfB,fcloser to unity, especially in orientations where the chamber axis is parallel to the magnetic field.
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Affiliation(s)
- Yunuen Cervantes
- Département de physique, Université de Montréal, Complexe des sciences, 1375 Avenue Thérèse-Lavoie-Roux, Montréal, Québec H2V 0B3, Canada.,Centre de recherche du Centre hospitalier de l'Université de Montréal, 900 Rue Saint-Denis, Montréal, Québec, H2X 0A9, Canada
| | - Jasmine Duchaine
- Département de physique, Université de Montréal, Complexe des sciences, 1375 Avenue Thérèse-Lavoie-Roux, Montréal, Québec H2V 0B3, Canada.,Centre de recherche du Centre hospitalier de l'Université de Montréal, 900 Rue Saint-Denis, Montréal, Québec, H2X 0A9, Canada
| | - Ilias Billas
- National Physical Laboratory, Chemical, Medical and Environmental Science Department, Teddington, United Kingdom.,Joint Department of Physics, The Institute of Cancer Research and The Royal Marsden NHS Foundation Trust, London, United Kingdom
| | - Simon Duane
- National Physical Laboratory, Chemical, Medical and Environmental Science Department, Teddington, United Kingdom
| | - Hugo Bouchard
- Département de physique, Université de Montréal, Complexe des sciences, 1375 Avenue Thérèse-Lavoie-Roux, Montréal, Québec H2V 0B3, Canada.,Centre de recherche du Centre hospitalier de l'Université de Montréal, 900 Rue Saint-Denis, Montréal, Québec, H2X 0A9, Canada.,Département de radio-oncologie, Centre hospitalier de l'Université de Montréal (CHUM), 900 Rue Saint-Denis, Montréal, Québec, H2X 0A9, Canada
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15
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Côté B, Keszti F, Bancheri J, Sarfehnia A, Seuntjens J, Renaud J. Feasibility of operating a millimeter-scale graphite calorimeter for absolute dosimetry of small-field photon beams in the clinic. Med Phys 2021; 48:7476-7492. [PMID: 34549805 DOI: 10.1002/mp.15244] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/09/2020] [Revised: 07/06/2021] [Accepted: 08/28/2001] [Indexed: 11/11/2022] Open
Abstract
PURPOSE To characterize and build a cylindrically layered graphite calorimeter the size of a thimble ionization chamber for absolute dosimetry of small fields. This detector has been designed in a familiar probe format to facilitate integration into the clinical workflow. The feasibility of operating this absorbed dose calorimeter in quasi-adiabatic mode is assessed for high-energy accelerator-based photon beams. METHODS This detector, herein referred to as Aerrow MK7, is a miniaturized version of a previously validated aerogel-insulated graphite calorimeter known as Aerrow. The new model was designed and developed using numerical methods. Medium conversion factors from graphite to water, small-field output correction factors, and layer perturbation factors for this dosimeter were calculated using the EGSnrc Monte Carlo code system. A range of commercially available aerogel densities were studied for the insulating layers, and an optimal density was selected by minimizing the small-field output correction factors. Heat exchange within the detector was simulated using a five-body compartmental heat transfer model. In quasi-adiabatic mode, the sensitive volume (a 3 mm diameter cylindrical graphite core) experiences a temperature rise during irradiation on the order of 1.3 mK·Gy-1 . The absorbed dose is obtained by calculating the product of this temperature rise with the specific heat capacity of the graphite. The detector was irradiated with 6 MV ( % dd ( 10 ) x = 63.5%) and 10 MV ( % dd ( 10 ) x = 71.1%) flattening filter-free (FFF) photon beams for two field sizes, characterized by S clin dimensions of 2.16 and 11.0 cm. The dose readings were compared against a calibrated Exradin A1SL ionization chamber. All dose values are reported at d max in water. RESULTS The field output correction factors for this dosimeter design were computed for field sizes ranging from S clin = 0.54 to 11.0 cm. For all aerogel densities studied, these correction factors did not exceed 1.5%. The relative dose difference between the two dosimeters ranged between 0.3% and 0.7% for all beams and field sizes. The smallest field size experimentally investigated, S clin = 2.16 cm, which was irradiated with the 10 MV FFF beam, produced readings of 84.4 cGy (±1.3%) in the calorimeter and 84.5 cGy (±1.3%) in the ionization chamber. CONCLUSION The median relative difference in absorbed dose values between a calibrated A1SL ionization chamber and the proposed novel graphite calorimeter was 0.6%. This preliminary experimental validation demonstrates that Aerrow MK7 is capable of accurate and reproducible absorbed dose measurements in quasi-adiabatic mode.
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Affiliation(s)
- Benjamin Côté
- Medical Physics Unit, Gerald Bronfman Department of Oncology, McGill University, Montreal, Quebec, Canada
| | - Federico Keszti
- Medical Physics Unit, Gerald Bronfman Department of Oncology, McGill University, Montreal, Quebec, Canada
| | - Julien Bancheri
- Medical Physics Unit, Gerald Bronfman Department of Oncology, McGill University, Montreal, Quebec, Canada
| | - Arman Sarfehnia
- Medical Physics Unit, Gerald Bronfman Department of Oncology, McGill University, Montreal, Quebec, Canada.,Department of Radiation Oncology, University of Toronto, Toronto, Ontario, Canada
| | - Jan Seuntjens
- Medical Physics Unit, Gerald Bronfman Department of Oncology, McGill University, Montreal, Quebec, Canada
| | - James Renaud
- Medical Physics Unit, Gerald Bronfman Department of Oncology, McGill University, Montreal, Quebec, Canada.,Metrology Research Centre, National Research Council Canada, Ottawa, Ontario, Canada
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16
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Khan AU, Simiele EA, DeWerd LA. Monte Carlo-derived ionization chamber correction factors in therapeutic carbon ion beams. Phys Med Biol 2021; 66. [PMID: 34464949 DOI: 10.1088/1361-6560/ac226c] [Citation(s) in RCA: 4] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/09/2021] [Accepted: 08/31/2021] [Indexed: 11/12/2022]
Abstract
The accuracy of electromagnetic transport in the GEANT4 Monte Carlo (MC) code was investigated for carbon ion beams and ionization chamber (IC)-specific beam quality correction factors were calculated. This work implemented a Fano cavity test for carbon ion beams in the 100-450 MeV/u energy range to assess the accuracy of the default electromagnetic physics parameters. TheUrbanand theWentzel-VImultiple Coulomb scattering models were evaluated and the impact ofmaxStep,dRover,andfinal rangeparameters on the accuracy of the transport algorithm was investigated. The optimal production thresholds for an accurate calculation offQvalues, which is the product of the water-to-air stopping power ratio and the IC-specific perturbation correction factor, were also studied. ThefQcorrection factors were calculated for a cylindrical and a parallel-plate IC using carbon ions in the 150-450 MeV/u energy range. Modifying the default electromagnetic physics parameters resulted in a maximum deviation from theory of 0.3%. Therefore, the default EM parameters were used for the remainder of this work. ThefQfactors were found to converge for both ICs with decreasing production threshold distance below 5μm. ThefQvalues obtained in this work agreed with the TRS-398 stopping power ratios and other previously reported results within uncertainty. This study highlights an accurate MC-based technique to calculate the combined stopping power ratio and the perturbation correction factor for any IC in carbon ion beams.
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Affiliation(s)
- Ahtesham Ullah Khan
- Department of Medical Physics, School of Medicine and Public Health, University of Wisconsin-Madison, Madison, WI 53705, United States of America
| | - Eric A Simiele
- Department of Radiation Oncology, Stanford University School of Medicine, Stanford, CA 94305, United States of America
| | - Larry A DeWerd
- Department of Medical Physics, School of Medicine and Public Health, University of Wisconsin-Madison, Madison, WI 53705, United States of America
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17
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Ding GX. Stopping-power ratios for electron beams used in total skin electron therapy. Med Phys 2021; 48:5472-5478. [PMID: 34287969 DOI: 10.1002/mp.15121] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/23/2021] [Revised: 06/28/2021] [Accepted: 07/12/2021] [Indexed: 11/10/2022] Open
Abstract
PURPOSE The electron beams for total skin electron therapy (TSET) are often degraded by a scatter plate in addition to extended distances. For electron dosimetry, both the AAPM TG-51 and IAEA TRS-398 recommend the use of two formulas developed by Burns et al [Med. Phys. 23, 489-501 (1996)] to estimate the water-to-air stopping-power ratios (SPRs). Both formulas are based on a fit to SPRs calculated for standard electron beams. This study aims to find: (1) if the formulas are applicable to beams used in TSET and (2) the impact of the ICRU report 90 recommendations on the SPRs for these beams. METHODS The EGSnrc Monte Carlo code system is used to generate 6 MeV high dose rate total skin electron (HDTSe) beams used in TSET. The simulated beams are used to calculate dose distributions and SPRs as a function of depth in a water phantom. The fitted SPRs using the empirical formulas are compared with MC-calculated SPRs. RESULTS The electron beam quality specifier, the depth in water at which the absorbed dose falls to 50% of its maximum value, R50 , decreases approximately 1 mm for each additional 100-cm extended distance ranging from 2.24 cm at SSD = 100 to 1.72 cm at SSD = 700 cm. For beams passing through a scatter plate, R50 is 1.76 cm (1.14) at SSD = 300 and 1.48 cm (0.85 cm) at SSD = 600 cm with an Acrylic plate thickness of 3 mm (9 mm), respectively. The discrepancy between fitted and MC-calculated SPRs at dref as a function of R50 is <0.8%, and in many cases <0.4%. The difference between fitted and MC-calculated SPRs as a function of depth and R50 is within 1% at depths <0.8R50 for beams with R50 ≥ 1.14 cm. The ICRU-90 recommendations decrease SPRs by 0.3%-0.4% compared to the use of data recommended in ICRU-37. CONCLUSION The formulas used by the major protocols are accurate enough for clinical beams used in TSET and the error caused using the formulas is <1% to estimate SPRs as a function of depth and R50 for depths <0.8R50 for beams used in TSET with R50 ≥ 1.14 cm. The impact of the ICRU-90 recommendations shows a decrease of SPRs by a fraction of a percent for beams used in TSET.
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Affiliation(s)
- George X Ding
- Department of Radiation Oncology, Vanderbilt University School of Medicine, Nashville, Tennessee, USA
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18
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Heng VJ, Serban M, Seuntjens J, Renaud MA. Ion chamber and film-based quality assurance of mixed electron-photon radiation therapy. Med Phys 2021; 48:5382-5395. [PMID: 34224144 DOI: 10.1002/mp.15081] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/16/2021] [Revised: 05/27/2021] [Accepted: 06/06/2021] [Indexed: 11/09/2022] Open
Abstract
PURPOSE In previous work, we demonstrated that mixed electron-photon radiation therapy (MBRT) produces treatment plans with improved normal tissue sparing and similar target coverage, when compared to photon-only plans. The purpose of this work was to validate the MBRT delivery process on a Varian TrueBeam accelerator and laying the groundwork for a patient-specific quality assurance (QA) protocol based on ion chamber point measurements and 2D film measurements. METHODS MC beam models used to calculate the MBRT dose distributions of each modality (photons/electrons) were validated with a single-angle beam MBRT treatment plan delivered on a slab of Solid Water phantom with a film positioned at a depth of 2 cm. The measured film absorbed dose was compared to the calculated dose. To validate clinical deliveries, a polymethyl methacrylate (PMMA) cylinder was machined and holes were made to fit an ionization chamber. A complex MBRT plan involving a photon arc and three electron delivery angles was created with the aim of reproducing a clinically realistic dose distribution in typical soft tissue sarcoma tumours of the extremities. The treatment plan was delivered on the PMMA cylinder. Point measurements were taken with an Exradin A1SL chamber at two nominal depths: 1.4 cm and 2.1 cm. The plan was also delivered on a second identical phantom with an insert at 2 cm depth, where a film was placed. An existing EGSnrc user-code, SPRRZnrc, was modified to calculate the stopping power ratios between any materials in the same voxelized geometry used for dose calculation purposes. This modified code, called SPRXYZnrc, was used to calculate a correction factor, k MBRT , accounting for the differences in electron fluence spectrum at the measurement point compared to that at reference conditions. The uncertainty associated with neglecting potential ionization chamber fluence perturbation correction factors using this approach was estimated. RESULTS The film measurement from the Solid Water phantom treatment plan was in good agreement with the simulated dose distribution, with a gamma pass rate of 96.1% for a 3%/2 mm criteria. For the PMMA phantom delivery, for the same gamma criteria, the pass rate was 97.3%. The ion chamber measurements of the total delivered dose agreed with the MC-simulated dose within 2.1%. The beam quality correction factors amounted to, at most, a 4% correction on the ion chamber measurement. However, individual contribution of low electron energies proved difficult to precisely measure due to their steep dose gradients, with disagreements of up to 28% ± 15% at 2.1 cm depth (6 MeV). Ion chamber measurement procedure of electron beams was achieved in less than 5 min, and the entire validation process including phantom setup was performed in less than 30 min. CONCLUSION The agreement between measured and simulated MBRT doses indicates that the dose distributions obtained from the MBRT treatment planning algorithm are realistically achievable. The SPRXYZnrc MC code allowed for convenient calculations of k MBRT simultaneously with the dose distributions, laying the groundwork for patient-specific QA protocol practical for clinical use. Further investigation is needed to establish the accuracy of our ionization chamber correction factors k MBRT calculations at low electron energies.
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Affiliation(s)
- Veng Jean Heng
- Department of Physics and Medical Physics Unit, McGill University, Montreal, QC, Canada
| | - Monica Serban
- Department of Medical Physics, McGill University Health Centre, Montreal, QC, Canada
| | - Jan Seuntjens
- Medical Physics Unit, McGill University and Research Institute of the McGill University Health Centre, Montreal, QC, Canada
| | - Marc-André Renaud
- Department of Mathematics and Industrial Engineering, Polytechnique Montréal, Montreal, QC, Canada
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Kamomae T, Matsunaga T, Suzuki J, Okudaira K, Kawabata F, Kato Y, Oguchi H, Shimizu M, Sasaki M, Takase Y, Kawamura M, Ohtakara K, Itoh Y, Naganawa S. Dosimetric impacts of beam-hardening filter removal for the CyberKnife system. Phys Med 2021; 86:98-105. [PMID: 34082183 DOI: 10.1016/j.ejmp.2021.05.011] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 02/16/2021] [Revised: 04/15/2021] [Accepted: 05/08/2021] [Indexed: 10/21/2022] Open
Abstract
PURPOSE Equipment refurbishment was performed to remove the beam-hardening filter (BHF) from the CyberKnife system (CK). This study aimed to confirm the change in the beam characteristics between the conventional CK (present-BHF CK) and CK after the BHF was removed (absent-BHF CK) and evaluate the impact of BHF removal on the beam quality correction factors kQ. METHODS The experimental measurements of the beam characteristics of the present- and absent-BHF CKs were compared. The CKs were modeled using Monte Carlo simulations (MCs). The energy fluence spectra were calculated using MCs. Finally, kQ were estimated by combining the MC results and analytic calculations based on the TRS-398 and TRS-483 approaches. RESULTS All gamma values for percent depth doses and beam profiles between each CK were less than 0.5 following the 3%/1 mm criteria. The percentage differences for tissue-phantom ratios at depths of 20 and 10 cm and percentage depth doses at 10 cm between each CK were -1.20% and -0.97%, respectively. The MC results demonstrated that the photon energy fluence spectrum of the absent-BHF CK was softer than that of the present-BHF CK. The kQ values for the absent-BHF CK were in agreement within 0.02% with those for the present-BHF CK. CONCLUSIONS The photon energy fluence spectrum was softened by the removal of BHF. However, no remarkable impact was observed for the measured beam characteristics and kQ. Therefore, the previous findings of the kQ values for the present-BHF CK can be directly used for the absent-BHF CK.
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Affiliation(s)
- Takeshi Kamomae
- Department of Radiology, Nagoya University Graduate School of Medicine, Nagoya, Aichi 466-8550, Japan.
| | - Takuma Matsunaga
- Radiotherapy Quality Management Group, TOYOTA Memorial Hospital, Toyota, Aichi 471-8513, Japan
| | - Junji Suzuki
- Radiotherapy Quality Management Group, TOYOTA Memorial Hospital, Toyota, Aichi 471-8513, Japan
| | - Kuniyasu Okudaira
- Department of Radiological Technology, Nagoya University Hospital, Nagoya, Aichi 466-8560, Japan
| | - Fumitaka Kawabata
- Department of Radiological Technology, Nagoya University Hospital, Nagoya, Aichi 466-8560, Japan
| | - Yutaka Kato
- Department of Radiological Technology, Nagoya University Hospital, Nagoya, Aichi 466-8560, Japan
| | - Hiroshi Oguchi
- Department of Radiological and Medical Laboratory Sciences, Nagoya University Graduate School of Medicine, Nagoya, Aichi 461-8673, Japan
| | - Morihito Shimizu
- National Metrology Institute of Japan, National Institute of Advanced Industrial Science and Technology (AIST), Tsukuba, Ibaraki 305-8568, Japan
| | - Motoharu Sasaki
- Department of Therapeutic Radiology, Institute of Biomedical Sciences, Tokushima University Graduate School, Tokushima, Tokushima 770-8503, Japan
| | - Yuki Takase
- Department of Radiology, Nagoya University Graduate School of Medicine, Nagoya, Aichi 466-8550, Japan
| | - Mariko Kawamura
- Department of Radiology, Nagoya University Graduate School of Medicine, Nagoya, Aichi 466-8550, Japan
| | - Kazuhiro Ohtakara
- Department of Radiology, Nagoya University Graduate School of Medicine, Nagoya, Aichi 466-8550, Japan
| | - Yoshiyuki Itoh
- Department of Radiology, Nagoya University Graduate School of Medicine, Nagoya, Aichi 466-8550, Japan
| | - Shinji Naganawa
- Department of Radiology, Nagoya University Graduate School of Medicine, Nagoya, Aichi 466-8550, Japan
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Calculations of magnetic field correction factors for ionization chambers in a transverse magnetic field using Monte Carlo code TOPAS. Radiat Phys Chem Oxf Engl 1993 2021. [DOI: 10.1016/j.radphyschem.2021.109405] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/19/2022]
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21
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de Pooter J, Billas I, de Prez L, Duane S, Kapsch RP, Karger CP, van Asselen B, Wolthaus J. Reference dosimetry in MRI-linacs: evaluation of available protocols and data to establish a Code of Practice. Phys Med Biol 2021; 66:05TR02. [PMID: 32570225 DOI: 10.1088/1361-6560/ab9efe] [Citation(s) in RCA: 25] [Impact Index Per Article: 8.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/22/2023]
Abstract
With the rapid increase in clinical treatments with MRI-linacs, a consistent, harmonized and sustainable ground for reference dosimetry in MRI-linacs is needed. Specific for reference dosimetry in MRI-linacs is the presence of a strong magnetic field. Therefore, existing Code of Practices (CoPs) are inadequate. In recent years, a vast amount of papers have been published in relation to this topic. The purpose of this review paper is twofold: to give an overview and evaluate the existing literature for reference dosimetry in MRI-linacs and to discuss whether the literature and datasets are adequate and complete to serve as a basis for the development of a new or to extend existing CoPs. This review is prefaced with an overview of existing MRI-linac facilities. Then an introduction on the physics of radiation transport in magnetic fields is given. The main part of the review is devoted to the evaluation of the literature with respect to the following subjects: • beam characteristics of MRI-linac facilities; • formalisms for reference dosimetry in MRI-linacs; • characteristics of ionization chambers in the presence of magnetic fields; • ionization chamber beam quality correction factors; and • ionization chamber magnetic field correction factors. The review is completed with a discussion as to whether the existing literature is adequate to serve as basis for a CoP. In addition, it highlights subjects for future research on this topic.
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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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Wakayama T, Ueda Y. [3. Measurement Practical Procedure or Technique of Photon Beam and Electron Beam]. Nihon Hoshasen Gijutsu Gakkai Zasshi 2021; 77:65-74. [PMID: 33473081 DOI: 10.6009/jjrt.2021_jsrt_77.1.65] [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]
Affiliation(s)
- Tsukasa Wakayama
- Department of Radiological Technology, Hyogo College of Medicine
| | - Yoshihiro Ueda
- Department of Radiation Oncology, Osaka International Center Institute
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Bouchard H. Reference dosimetry of modulated and dynamic photon beams. Phys Med Biol 2021; 65:24TR05. [PMID: 33438582 DOI: 10.1088/1361-6560/abc3fb] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/12/2022]
Abstract
In the late 1980s, a new technique was proposed that would revolutionize radiotherapy. Now referred to as intensity-modulated radiotherapy, it is at the core of state-of-the-art photon beam delivery techniques, such as helical tomotherapy and volumetric modulated arc therapy. Despite over two decades of clinical application, there are still no established guidelines on the calibration of dynamic modulated photon beams. In 2008, the IAEA-AAPM work group on nonstandard photon beam dosimetry published a formalism to support the development of a new generation of protocols applicable to nonstandard beam reference dosimetry (Alfonso et al 2008 Med. Phys. 35 5179-86). The recent IAEA Code of Practice TRS-483 was published as a result of this initiative and addresses exclusively small static beams. But the plan-class specific reference calibration route proposed by Alfonso et al (2008 Med. Phys. 35 5179-86) is a change of paradigm that is yet to be implemented in radiotherapy clinics. The main goals of this paper are to provide a literature review on the dosimetry of nonstandard photon beams, including dynamic deliveries, and to discuss anticipated benefits and challenges in a future implementation of the IAEA-AAPM formalism on dynamic photon beams.
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Affiliation(s)
- Hugo Bouchard
- Département de physique, Université de Montréal, Complexe des sciences, 1375 Avenue Thérèse-Lavoie-Roux, Montréal, Québec H2V 0B3, Canada. Centre de recherche du Centre hospitalier de l'Université de Montréal, 900 Rue Saint-Denis, Montréal, Québec H2X 0A9, Canada. Département de radio-oncologie, Centre hospitalier de l'Université de Montréal (CHUM), 1051 Rue Sanguinet, Montréal, Québec H2X 3E4, Canada
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Cervantes Y, Billas I, Shipley D, Duane S, Bouchard H. Small-cavity chamber dose response in megavoltage photon beams coupled to magnetic fields. Phys Med Biol 2020; 65:245008. [PMID: 32674077 DOI: 10.1088/1361-6560/aba6d6] [Citation(s) in RCA: 8] [Impact Index Per Article: 2.0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/12/2022]
Abstract
In MRgRT, dosimetry measurements are performed in the presence of magnetic fields. For high-resolution measurements, small-cavity ionization chambers are required. While Monte Carlo simulations are essential to determine dosimetry correction factors, models of small-chambers require careful validation with experimental measurements. The aim of this study is to characterize small-cavity chamber response coupled to magnetic fields. Small-cavity chambers (PTW31010, PTW31016, PTW31021 and PTW3022) are irradiated by a 6 MV photon beam for 9 magnetic field strengths between -1.5 T and +1.5 T. The chamber axis is orientated either parallel or perpendicular to the irradiation beam, with the magnetic field always perpendicular to the beam. MC simulations are performed in EGSnrc. The sensitive volume of the chambers is reduced to account for the inefficiency adjacent to the guard electrode (dead volume) based on COMSOL calculations of electric potentials. The magnetic field affects the chamber response by up to 4.1% and 4.5% in the parallel and perpendicular orientations, respectively, compared to no magnetic field. The maximal difference in dose response between experiments and simulations is up to 6.1% and 4.5% for parallel and perpendicular orientation, respectively. When the dead volume is removed, which accounts for the 15%-23% of the nominal volume, the difference, in most cases, is within the stated uncertainties. Nevertheless, for a particular chamber, the reduced nominal volume barely improved the agreement between the experimental and calculated relative response (4.53% to 4.13%). This disagreement may be due to the imperfect chamber geometry model, as was found from microCT images. A detailed uncertainty analysis is presented. The characterization of small-cavity ion chamber response coupled to magnetic fields is complex. Small differences between real and model chamber geometry that normally would be insignificant become an issue in the presence of magnetic fields. Accurate characterization of the nominal volume is essential for small-cavity ion chamber modelling.
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Affiliation(s)
- Yunuen Cervantes
- Département de physique, Université de Montréal, Complexe des sciences, 1375 Avenue Thérèse-Lavoie-Roux, Montréal, Québec H2V 0B3, Canada. Centre de recherche du Centre hospitalier de l'Université de Montréal, 900 Rue Saint-Denis, Montréal, Québec, H2X 0A9, Canada
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Giménez-Alventosa V, Giménez V, Ballester F, Vijande J, Andreo P. Monte Carlo calculation of beam quality correction factors for PTW cylindrical ionization chambers in photon beams. ACTA ACUST UNITED AC 2020; 65:205005. [DOI: 10.1088/1361-6560/ab9501] [Citation(s) in RCA: 4] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/11/2022]
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Rossi G, Gainey M, Kollefrath M, Hofmann E, Baltas D. Suitability of the microDiamond detector for experimental determination of the anisotropy function of High Dose Rate 192 Ir brachytherapy sources. Med Phys 2020; 47:5838-5851. [PMID: 32970875 DOI: 10.1002/mp.14488] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/18/2019] [Revised: 09/07/2020] [Accepted: 09/13/2020] [Indexed: 11/06/2022] Open
Abstract
PURPOSE To investigate the suitability of the microDiamond detector (mDD) type 60019 (PTW-Freiburg, Germany) to measure the anisotropy function F(r,θ) of High Dose Rate (HDR) 192 Ir brachytherapy sources. METHODS The HDR 192 Ir brachytherapy source, model mHDR-v2r (Elekta AB, Sweden), was placed inside a water tank within a 4F plastic needle. Four mDDs (mDD1, mDD2, mDD3, and mDD4) were investigated. Each mDD was placed laterally with respect to the source, and measurements were performed at radial distances r = 1 cm, 3 and 5 cm, and polar angles θ from 0° to 168°. The Monte Carlo (MC) system EGSnrc was used to simulate the measurements and to calculate phantom effect, energy dependence and volume-averaging correction factors. F(r,θ) was determined according to TG-43 formalism from the detector reading corrected with the MC-based factors and compared to the consensus anisotropy function CON F(r,θ). RESULTS At 1 cm, the differences between measurements and MC simulations ranged from -0.8% to +0.8% for θ = 0° and from -2.1% to + 2.3% for θ ≠ 0°. At 3 and 5 cm, the differences ranged from +1.4% to +3.9% for θ = 0°, and from -0.4% to +2.9% for θ ≠ 0°. All differences were within the uncertainties (k = 2). At small angles, the phantom effect correction was up to -1.9%. This effect was mainly caused by the air between source and needle tip. The energy correction was angle-independent everywhere. For small angles at 1 cm, the volume-averaging correction was up to -2.9% and became less important for larger angles and distances. The differences of the measured F(r,θ) corrected with the MC-based factors to CON F(r,θ) ranged from -1.0% to +3.4% for mDD1, -2.2% to +4.2% for mDD2, -2.5% to +4.0% for mDD3, and -2.6% to +3.4% for mDD4. All differences were within the uncertainties (k = 2) except one at (3 cm, 0°). For all the mDDs, F(r,0°) was always higher than CON F(r,0°), with average differences of +3.1% (1 cm), +3.6% (3 cm), and +1.9% (5 cm). The inter-detector variability was within 2.9% (1 cm), 1.8% (3 cm), and 3.4% (5 cm). CONCLUSIONS A reproducible method and experimental setup were presented for measuring and validating F(r,θ) of an HDR 192 Ir brachytherapy source in a water phantom using the mDD. The phantom effect and the volume-averaging need to be taken into account, especially for the smaller distances and angles. Good agreement to CON F(r,θ) was obtained. The discrepancies at (1 cm, 0°), accurately predicted by the MC results, may suggest a reconsideration of CON F(r,θ), at least for this position. The slight overestimations at (3 cm,0°) and (5 cm,0°), both in comparison to CON F(r,θ) and MC results, may be due to an underestimation of the air volume between source and needle tip, dark current, intrinsic over-response of the mDDs, or radiation-induced charge imbalance in the detector's components. The results indicate that the mDD is a valuable tool for measurements with HDR 192 Ir brachytherapy sources and support its employment for the determination and validation of TG-43 parameters of such sources.
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Affiliation(s)
- Giulio Rossi
- Division of Medical Physics, Department of Radiation Oncology, Medical Center, Faculty of Medicine, University of Freiburg, German Cancer Consortium (DKTK) Partner Site Freiburg, German Cancer Research Center (DKFZ), Heidelberg, Germany
| | - Mark Gainey
- Division of Medical Physics, Department of Radiation Oncology, Medical Center, Faculty of Medicine, University of Freiburg, German Cancer Consortium (DKTK) Partner Site Freiburg, German Cancer Research Center (DKFZ), Heidelberg, Germany
| | - Michael Kollefrath
- Division of Medical Physics, Department of Radiation Oncology, Medical Center, Faculty of Medicine, University of Freiburg, German Cancer Consortium (DKTK) Partner Site Freiburg, German Cancer Research Center (DKFZ), Heidelberg, Germany
| | - Elena Hofmann
- Division of Medical Physics, Department of Radiation Oncology, Medical Center, Faculty of Medicine, University of Freiburg, German Cancer Consortium (DKTK) Partner Site Freiburg, German Cancer Research Center (DKFZ), Heidelberg, Germany
| | - Dimos Baltas
- Division of Medical Physics, Department of Radiation Oncology, Medical Center, Faculty of Medicine, University of Freiburg, German Cancer Consortium (DKTK) Partner Site Freiburg, German Cancer Research Center (DKFZ), Heidelberg, Germany
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Buchegger N, Grogan G, Hug B, Oliver C, Ebert M. CyberKnife reference dosimetry: An assessment of the impact of evolving recommendations on correction factors and measured dose. Med Phys 2020; 47:3573-3585. [DOI: 10.1002/mp.14190] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/06/2019] [Revised: 03/29/2020] [Accepted: 03/30/2020] [Indexed: 11/06/2022] Open
Affiliation(s)
- Nicole Buchegger
- Department of Radiation Oncology Sir Charles Gairdner Hospital Nedlands WA 6009 Australia
| | - Garry Grogan
- Department of Radiation Oncology Sir Charles Gairdner Hospital Nedlands WA 6009 Australia
| | - Ben Hug
- 5D Clinics Claremont WA 6010 Australia
| | - Chris Oliver
- Australian Radiation Protection and Nuclear Safety Agency Yallambie Vic. 3085 Australia
| | - Martin Ebert
- Department of Radiation Oncology Sir Charles Gairdner Hospital Nedlands WA 6009 Australia
- 5D Clinics Claremont WA 6010 Australia
- Department of Physics University of Western Australia Crawley WA 6009 Australia
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Becker SJ, Culberson WS, Poirier Y, Mutaf Y, Niu Y, Nichols EM, Yi B. Dosimetry evaluation of the GammaPod stereotactic radiosurgery device based on established AAPM and IAEA protocols. Med Phys 2020; 47:3614-3620. [DOI: 10.1002/mp.14197] [Citation(s) in RCA: 4] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/11/2019] [Revised: 03/23/2020] [Accepted: 04/08/2020] [Indexed: 11/06/2022] Open
Affiliation(s)
- Stewart J. Becker
- Department of Radiation Oncology University of Maryland School of Medicine Baltimore MD 21201 USA
| | - Wesley S. Culberson
- Department of Medical Physics University of Wisconsin–Madison Madison Wisconsin 53705 USA
| | - Yannick Poirier
- Department of Radiation Oncology University of Maryland School of Medicine Baltimore MD 21201 USA
| | - Yildirim Mutaf
- Department of Radiation Oncology University of Maryland School of Medicine Baltimore MD 21201 USA
| | - Ying Niu
- MedStar Georgetown University Hospital Washington DC 20007 USA
| | - Elizabeth M. Nichols
- Department of Radiation Oncology University of Maryland School of Medicine Baltimore MD 21201 USA
| | - Byongyong Yi
- Department of Radiation Oncology University of Maryland School of Medicine Baltimore MD 21201 USA
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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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31
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Andreo P, Burns DT, Kapsch RP, McEwen M, Vatnitsky S, Andersen CE, Ballester F, Borbinha J, Delaunay F, Francescon P, Hanlon MD, Mirzakhanian L, Muir B, Ojala J, Oliver CP, Pimpinella M, Pinto M, de Prez LA, Seuntjens J, Sommier L, Teles P, Tikkanen J, Vijande J, Zink K. Determination of consensus k Q values for megavoltage photon beams for the update of IAEA TRS-398. ACTA ACUST UNITED AC 2020; 65:095011. [DOI: 10.1088/1361-6560/ab807b] [Citation(s) in RCA: 18] [Impact Index Per Article: 4.5] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/12/2022]
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32
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Tikkanen J, Zink K, Pimpinella M, Teles P, Borbinha J, Ojala J, Siiskonen T, Gomà C, Pinto M. Calculated beam quality correction factors for ionization chambers in MV photon beams. Phys Med Biol 2020; 65:075003. [PMID: 31995531 DOI: 10.1088/1361-6560/ab7107] [Citation(s) in RCA: 7] [Impact Index Per Article: 1.8] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/12/2022]
Abstract
The beam quality correction factor, [Formula: see text], which corrects for the difference in the ionization chamber response between the reference and clinical beam quality, is an integral part of radiation therapy dosimetry. The uncertainty of [Formula: see text] is one of the most significant sources of uncertainty in the dose determination. To improve the accuracy of available [Formula: see text] data, four partners calculated [Formula: see text] factors for 10 ionization chamber models in linear accelerator beams with accelerator voltages ranging from 6 MV to 25 MV, including flattening-filter-free (FFF) beams. The software used in the calculations were EGSnrc and PENELOPE, and the ICRU report 90 cross section data for water and graphite were included in the simulations. Volume averaging correction factors were calculated to correct for the dose averaging in the chamber cavities. A comparison calculation between partners showed a good agreement, as did comparison with literature. The [Formula: see text] values from TRS-398 were higher than our values for each chamber where data was available. The [Formula: see text] values for the FFF beams did not follow the same [Formula: see text], [Formula: see text] relation as beams with flattening filter (values for 10 MV FFF beams were below fits made to other data on average by 0.3%), although our FFF sources were only for Varian linacs.
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Affiliation(s)
- J Tikkanen
- Radiation and Nuclear Safety Authority (STUK), Helsinki, Finland. Helsinki Institute of Physics, University of Helsinki, Helsinki, Finland
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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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34
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Renaud J, Palmans H, Sarfehnia A, Seuntjens J. Absorbed dose calorimetry. ACTA ACUST UNITED AC 2020; 65:05TR02. [DOI: 10.1088/1361-6560/ab4f29] [Citation(s) in RCA: 11] [Impact Index Per Article: 2.8] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/16/2023]
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35
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Renaud J, Sarfehnia A, Bancheri J, Seuntjens J. Absolute dosimetry of a 1.5 T MR-guided accelerator-based high-energy photon beam in water and solid phantoms using Aerrow. Med Phys 2019; 47:1291-1304. [PMID: 31834640 DOI: 10.1002/mp.13968] [Citation(s) in RCA: 7] [Impact Index Per Article: 1.4] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/02/2019] [Revised: 12/03/2019] [Accepted: 12/05/2019] [Indexed: 11/09/2022] Open
Abstract
PURPOSE In this work, the fabrication, operation, and evaluation of a probe-format graphite calorimeter - herein referred to as Aerrow - as an absolute clinical dosimeter of high-energy photon beams while in the presence of a B = 1.5 T magnetic field is described. Comparable to a cylindrical ionization chamber (IC) in terms of utility and usability, Aerrow has been developed for the purpose of accurately measuring absorbed dose to water in the clinic with a minimum disruption to the existing clinical workflow. To our knowledge, this is the first reported application of graphite calorimetry to magnetic resonance imaging (MRI)-guided radiotherapy. METHODS Based on a previously numerically optimized and experimentally validated design, an Aerrow prototype capable of isothermal operation was constructed in-house. Graphite-to-water dose conversions as well as magnetic field perturbation factors were calculated using Monte Carlo, while heat transfer and mass impurity corrections and uncertainties were assessed analytically. Reference dose measurements were performed in the absence and presence of a B = 1.5 T magnetic field using Aerrow in the 7 MV FFF photon beam of an Elekta MRI-linac and were directly compared to the results obtained using two calibrated reference-class IC types. The feasibility of performing solid phantom-based dosimetry with Aerrow and the possible influence of clearance gaps is also investigated by performing reference-type dosimetry measurements for multiple rotational positions of the detector and comparing the results to those obtained in water. RESULTS In the absence of the B-field, as well as in the parallel orientation while in the presence of the B-field, the absorbed dose to water measured using Aerrow was found to agree within combined uncertainties with those derived from TG-51 using calibrated reference-class ICs. Statistically significant differences on the order of (2-4)%, however, were observed when measuring absorbed dose to water using the ICs in the perpendicular orientation in the presence of the B-field. Aerrow had a peak-to-peak response of about 0.5% when rotated within the solid phantom regardless of whether the B-field was present or not. CONCLUSIONS This work describes the successful use of Aerrow as a straightforward means of measuring absolute dose to water for large high-energy photon fields in the presence of a 1.5 T B-field to a greater accuracy than currently achievable with ICs. The detector-phantom air gap does not appear to significantly influence the response of Aerrow in absolute terms, nor does it contribute to its rotational dependence. This work suggests that the accurate use of solid phantoms for absolute point dose measurement is possible with Aerrow.
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Affiliation(s)
- James Renaud
- Metrology Research Centre, National Research Council Canada, Ottawa, ON, K1T 0R6, Canada.,Medical Physics Unit, McGill University, Montréal, QC, H4A 3J1, Canada
| | - Arman Sarfehnia
- Medical Physics Unit, McGill University, Montréal, QC, H4A 3J1, Canada.,Department of Radiation Oncology, University of Toronto, Toronto, ON, M5S 3E2, Canada
| | - Julien Bancheri
- Medical Physics Unit, McGill University, Montréal, QC, H4A 3J1, Canada
| | - Jan Seuntjens
- Medical Physics Unit, McGill University, Montréal, QC, H4A 3J1, Canada
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Baumann K, Horst F, Zink K, Gomà C. Comparison of penh, fluka, and Geant4/topas for absorbed dose calculations in air cavities representing ionization chambers in high-energy photon and proton beams. Med Phys 2019; 46:4639-4653. [PMID: 31350915 PMCID: PMC6851981 DOI: 10.1002/mp.13737] [Citation(s) in RCA: 19] [Impact Index Per Article: 3.8] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/03/2018] [Revised: 07/01/2019] [Accepted: 07/16/2019] [Indexed: 12/16/2022] Open
Abstract
PURPOSE The purpose of this work is to analyze whether the Monte Carlo codes penh, fluka, and geant4/topas are suitable to calculate absorbed doses andf Q / f Q 0 ratios in therapeutic high-energy photon and proton beams. METHODS We used penh, fluka, geant4/topas, and egsnrc to calculate the absorbed dose to water in a reference water cavity and the absorbed dose to air in two air cavities representative of a plane-parallel and a cylindrical ionization chamber in a 1.25 MeV photon beam and a 150 MeV proton beam - egsnrc was only used for the photon beam calculations. The physics and transport settings in each code were adjusted to simulate the particle transport as detailed as reasonably possible. From these absorbed doses, f Q 0 factors, f Q factors, andf Q / f Q 0 ratios (which are the basis of Monte Carlo calculated beam quality correction factors k Q , Q 0 ) were calculated and compared between the codes. Additionally, we calculated the spectra of primary particles and secondary electrons in the reference water cavity, as well as the integrated depth-dose curve of 150 MeV protons in water. RESULTS The absorbed doses agreed within 1.4% or better between the individual codes for both the photon and proton simulations. The f Q 0 and f Q factors agreed within 0.5% or better for the individual codes for both beam qualities. The resultingf Q / f Q 0 ratios for 150 MeV protons agreed within 0.7% or better. For the 1.25 MeV photon beam, the spectra of photons and secondary electrons agreed almost perfectly. For the 150 MeV proton simulation, we observed differences in the spectra of secondary protons whereas the spectra of primary protons and low-energy delta electrons also agreed almost perfectly. The first 2 mm of the entrance channel of the 150 MeV proton Bragg curve agreed almost perfectly while for greater depths, the differences in the integrated dose were up to 1.5%. CONCLUSION penh, fluka, and geant4/topas are capable of calculating beam quality correction factors in proton beams. The differences in the f Q 0 and f Q factors between the codes are 0.5% at maximum. The differences in thef Q / f Q 0 ratios are 0.7% at maximum.
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Affiliation(s)
- Kilian‐Simon Baumann
- Department of Radiotherapy and RadiooncologyUniversity Medical Center Giessen‐MarburgMarburgGermany
- Institute of Medical Physics and Radiation ProtectionUniversity of Applied SciencesGiessenGermany
| | - Felix Horst
- Institute of Medical Physics and Radiation ProtectionUniversity of Applied SciencesGiessenGermany
- GSI Helmholtzzentrum für SchwerionenforschungDarmstadtGermany
| | - Klemens Zink
- Department of Radiotherapy and RadiooncologyUniversity Medical Center Giessen‐MarburgMarburgGermany
- Institute of Medical Physics and Radiation ProtectionUniversity of Applied SciencesGiessenGermany
- Frankfurt Institute for Advanced Studies (FIAS)FrankfurtGermany
| | - Carles Gomà
- Department of Oncology, Laboratory of Experimental RadiotherapyKU LeuvenLeuvenBelgium
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37
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Kawachi T, Saitoh H, Katayose T, Tohyama N, Miyasaka R, Cho SY, Iwase T, Hara R. Effect of ICRU report 90 recommendations on Monte Carlo calculated k Q for ionization chambers listed in the Addendum to AAPM's TG-51 protocol. Med Phys 2019; 46:5185-5194. [PMID: 31386762 DOI: 10.1002/mp.13743] [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: 12/07/2018] [Revised: 07/11/2019] [Accepted: 07/19/2019] [Indexed: 11/10/2022] Open
Abstract
PURPOSE The ICRU has published new recommendations for ionizing radiation dosimetry. In this work, the effect of recommendations on the water-to-air and graphite-to-air restricted mass electronic stopping power ratios (sw, air and sg, air ) and the individual perturbation correction factors Pi was calculated. The effect on the beam quality conversion factors kQ for reference dosimetry of high-energy photon beams was estimated for all ionization chambers listed in the Addendum to AAPM's TG-51 protocol. METHODS The sw, air , sg, air , individual Pi, and kQ were calculated using EGSnrc Monte Carlo code system and key data of both ICRU report 37 and ICRU report 90. First, the Pi and kQ were calculated using precise models of eight ionization chambers: NE2571 (Nuclear Enterprise), 30013, 31010, 31021 (PTW), Exradin A12, A12S, A1SL (Standard imaging), and FC-65P (IBA). In this simulation, the radiation sources were one 60 Co beam and ten photon beams with nominal energy between 4 MV and 25 MV. Then, the change in kQ for ionization chambers listed in the Addendum to AAPM's TG-51 protocol was calculated by changing the specification of the simple-model of ionization chamber. The simple-models were made with only cylindrical component modules. In this simulation, the radiation sources of 60 Co beam and 24 MV photon beam were used. RESULTS The significant changes (p < 0.05) were observed for sw, air , sg, air , the wall correction factor Pwall , and the waterproofing sleeve correction factor Psleeve . The decrease in sw, air varied from -0.57% for a 60 Co beam to -0.36% for the highest beam quality. The decrease in sg, air varied from -0.72% to -1.12% in the same range. The changes in Pwall and Psleeve were up to 0.41% and 0.14% and those maximum changes were observed for the 60 Co beam. All changes in the central electrode correction factor Pcel , the stem correction factor Pstem , and the replacement correction factor Prepl were from -0.02% to 0.12%. Those changes were statistically insignificant (p = 0.07 or more) and were independent of photon energy. The change in kQ was mainly characterized by the change in sw, air , Pwall , and Psleeve . The relationship between the change in kQ and the beam quality index was linear approximately. The changes in kQ of the simple-models were agreed with those of the precise-models within 0.08%. CONCLUSION The effects of ICRU-90 recommendations on kQ for the ionization chambers listed in the Addendum to AAPM's TG-51 protocol were from -0.15% to 0.30%. To remove the known systematic effect on the clinical reference dosimetry, the kQ based on ICRU-37 should be updated to the kQ based on ICRU-90.
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Affiliation(s)
- Toru Kawachi
- Division of Radiation Oncology, Chiba Cancer Center, Chiba, Chiba, 260-8717, Japan.,Graduate School of Human Health Sciences, Tokyo Metropolitan University, Arakawa, Tokyo, 116-8551, Japan
| | - Hidetoshi Saitoh
- Graduate School of Human Health Sciences, Tokyo Metropolitan University, Arakawa, Tokyo, 116-8551, Japan
| | - Tetsurou Katayose
- Division of Radiation Oncology, Chiba Cancer Center, Chiba, Chiba, 260-8717, Japan
| | - Naoki Tohyama
- Division of Medical Physics, Tokyo Bay Advanced Imaging & Radiation Oncology Makuhari Clinic, Chiba, 261-0024, Japan
| | - Ryohei Miyasaka
- Division of Radiation Oncology, Chiba Cancer Center, Chiba, Chiba, 260-8717, Japan
| | - Sang Yong Cho
- Division of Radiation Oncology, Chiba Cancer Center, Chiba, Chiba, 260-8717, Japan
| | - Tsutomu Iwase
- Division of Radiation Oncology, Chiba Cancer Center, Chiba, Chiba, 260-8717, Japan
| | - Ryusuke Hara
- Division of Radiation Oncology, Chiba Cancer Center, Chiba, Chiba, 260-8717, Japan
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Büsing I, Brant A, Lange T, Delfs B, Poppinga D, Kranzer R, Looe HK, Poppe B. Experimental and Monte-Carlo characterization of the novel compact ionization chamber PTW 31023 for reference and relative dosimetry in high energy photon beams. Z Med Phys 2019; 29:303-313. [PMID: 30878324 DOI: 10.1016/j.zemedi.2019.02.002] [Citation(s) in RCA: 5] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/05/2018] [Revised: 02/20/2019] [Accepted: 02/20/2019] [Indexed: 11/17/2022]
Abstract
INTRODUCTION The aim of the present work is to perform dosimetric characterization of a novel vented PinPoint ionization chamber (PTW 31023, PTW-Freiburg, Germany). This chamber replaces the previous model (PTW 31014), where the diameter of the central electrode has been increased from 0.3 to 0.6mm and the guard ring has been redesigned. Correction factors for reference and non-reference measurement conditions were examined. MATERIALS AND METHODS Measurements and calculations of the correction factors were performed according to the DIN 6800-2. The shifts of the effective point of measurement (EPOM) from the chamber's reference point were determined by comparison of the measured PDD with the reference curve obtained with a Roos chamber. Its lateral dose response functions, which act according to a mathematical convolution model as the convolution kernel transforming the dose profile D(x) to the measured signal M(x), have been approximated by Gaussian functions with standard deviation σ. Additionally, the saturation correction factors kS have been determined using different dose-per-pulse (DPP) values. The polarity effect correction factors kP were measured for field sizes from 5cm×5cm to 40cm×40cm. The influence of the diameter of the central electrode and the new guard ring on the beam quality correction factors kQ was studied by Monte-Carlo simulations. The non-reference condition correction factors kNR have been computed for 6MV photo beam by varying the field size and measurement depth. Comparisons on these aspects have been made to the previous model. RESULTS The shifts of the EPOM from the reference point, Δz, are found to be -0.55 (6MV) and -0.56 (10MV) in the radial orientation and -0.97mm (6MV) and -0.91mm (10MV) in the axial orientation. All values of Δz have an uncertainty of 0.1mm. The σ values are 0.80mm (axial), 0.75mm (radial lateral) and 1.76mm (radial longitudinal) for 6MV photon beam and are 0.85mm (axial), 0.75mm (radial lateral) and 1.82mm (radial longitudinal) for 15MV photon beam. All σ values have an uncertainty of 0.05mm. The correction factor kS was found to be 1.0034±0.0009 for the PTW 31014 chamber and 1.0024±0.0007 for the PTW 31023 chamber at the highest DPP (0.827mGy) investigated in this study. Under reference conditions, the polarity effect correction factor kP of the PTW 31014 chamber is 1.0094 and 1.0116 for 6 and 10MV respectively, while the kP of the PTW 31023 chamber is 1.0005 and 1.0013 for 6 and 10MV respectively, all values have an uncertainty of 0.002. The kP of the new chamber also exhibits a weaker field size dependence. The kQ values of the PTW 31023 chamber are closer to unity than those of the PTW 31014 chamber due to the thicker central electrode and the new guard ring design. The kNR values of the PTW 31023 chamber for 6MV photon beam deviate by not more than 1% from unity for the conditions investigated. DISCUSSIONS Correction factors associated with the new chamber required to perform reference and relative dose measurements have been determined according to the DIN-protocol. The correction factor kS of the new chamber is 0.1% smaller than that of the PTW 31014 at the highest DPP investigated. Under reference conditions, the correction factor kP of the PTW 31023 chamber is approximately 1% smaller than that of the PTW 31014 chamber for both energies used. The dosimetric characteristics of the new chamber investigated in this work have been demonstrated to fulfil the requirements of the TG-51 addendum for reference-class dosimeters at reference conditions.
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Affiliation(s)
- Isabel Büsing
- University Clinic for Medical Radiation Physics, Medical Campus Pius Hospital, Carl von Ossietzky University, Oldenburg, Germany.
| | - Andre Brant
- University Clinic for Medical Radiation Physics, Medical Campus Pius Hospital, Carl von Ossietzky University, Oldenburg, Germany
| | - Tobias Lange
- University Clinic for Medical Radiation Physics, Medical Campus Pius Hospital, Carl von Ossietzky University, Oldenburg, Germany
| | - Björn Delfs
- University Clinic for Medical Radiation Physics, Medical Campus Pius Hospital, Carl von Ossietzky University, Oldenburg, Germany
| | | | | | - Hui Khee Looe
- University Clinic for Medical Radiation Physics, Medical Campus Pius Hospital, Carl von Ossietzky University, Oldenburg, Germany
| | - Björn Poppe
- University Clinic for Medical Radiation Physics, Medical Campus Pius Hospital, Carl von Ossietzky University, Oldenburg, Germany
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Bancheri J, Seuntjens J, Sarfehnia A, Renaud J. Density effects of silica aerogel insulation on the performance of a graphite probe calorimeter. Med Phys 2019; 46:1874-1882. [DOI: 10.1002/mp.13426] [Citation(s) in RCA: 7] [Impact Index Per Article: 1.4] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/12/2018] [Revised: 01/02/2019] [Accepted: 01/17/2019] [Indexed: 11/07/2022] Open
Affiliation(s)
- Julien Bancheri
- Medical Physics Unit McGill University Montréal QC H4A 3J1Canada
| | - Jan Seuntjens
- Medical Physics Unit McGill University Montréal QC H4A 3J1Canada
| | - Arman Sarfehnia
- Medical Physics Unit McGill University Montréal QC H4A 3J1Canada
- Department of Radiation Oncology University of Toronto Toronto ON M5S 3E2Canada
| | - James Renaud
- Medical Physics Unit McGill University Montréal QC H4A 3J1Canada
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Delfs B, Kapsch RP, Chofor N, Looe HK, Harder D, Poppe B. A new reference-type ionization chamber with direction-independent response for use in small-field photon-beam dosimetry – An experimental and Monte Carlo study. Z Med Phys 2019; 29:39-48. [DOI: 10.1016/j.zemedi.2018.05.001] [Citation(s) in RCA: 7] [Impact Index Per Article: 1.4] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/05/2017] [Revised: 04/18/2018] [Accepted: 05/04/2018] [Indexed: 10/14/2022]
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Pimpinella M, Silvi L, Pinto M. Calculation of kQ factors for Farmer-type ionization chambers following the recent recommendations on new key dosimetry data. Phys Med 2019; 57:221-230. [DOI: 10.1016/j.ejmp.2018.12.006] [Citation(s) in RCA: 6] [Impact Index Per Article: 1.2] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 07/31/2018] [Revised: 11/08/2018] [Accepted: 12/10/2018] [Indexed: 10/27/2022] Open
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Reynolds M, St-Aubin J. Monte Carlo determination of k Q and k Qmsr values for the exradin A26 ionisation chamber for the Varian TrueBeam. Phys Med Biol 2018; 63:195006. [PMID: 30207987 DOI: 10.1088/1361-6560/aae0e9] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/12/2022]
Abstract
We have calculated conversion factors, k Q for the A26 micro ionisation chamber along with machine specific reference beam quality factors, k Qmsr, for a number of field sizes and beam qualities for the Varian TrueBeam accelerator. The A12 ionisation chamber was simulated alongside the A26, so as to validate against known literature values. Both ionisation chambers were modelled from manufacturer data sheets and schematics. The egs_chamber Monte Carlo user code was used to simulate each absorbed dose relevant to the beam quality conversion factors k Q and k Qmsr. Tabulated spectra for beam energies of 4 through 25 MV were used in the k Q calculations for both investigated chambers. Varian TrueBeam phase space files for 6 MV flattened as well as 6 and 10 MV unflattened beams were used in the simulations of the A26 chamber in field sizes from 2 × 2 cm square to 20 × 20 cm square in order to determine k Qmsr values. The PDD(10)x values of the tabulated spectra were found to be within variation between studies, with an average deviance of 0.4% from one prior study. The simulated A12 k Q values matched the accepted literature values with an average variation of <0.1%. The A26 k Q values match the manufacturer provided values to within 0.5%. For all investigated field sizes the k Qmsr values are within 0.006 of unity. There is no published data for this chamber for a direct comparison, but there is similarity between these results and results from other chambers regularly used in similar circumstances. Furthermore, the agreement of the simulated k Q values to knowns, and the agreement of the PDD(10)x factors would suggest the correctness and accuracy of the study.
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Affiliation(s)
- M Reynolds
- Department of Oncology, Medical Physics Division, University of Alberta, 11560 University Avenue, Edmonton, Alberta T6G 1Z2, Canada. Author to whom correspondence should be addressed
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Araki F, Ohno T, Umeno S. Ionization chamber dosimetry based on 60Co absorbed dose to water calibration for diagnostic kilovoltage x-ray beams. ACTA ACUST UNITED AC 2018; 63:185018. [DOI: 10.1088/1361-6560/aad9c0] [Citation(s) in RCA: 5] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/12/2022]
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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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Mainegra-Hing E, Muir BR. On the impact of ICRU report 90 recommendations on k Q factors for high-energy photon beams. Med Phys 2018; 45:3904-3908. [PMID: 29862534 DOI: 10.1002/mp.13027] [Citation(s) in RCA: 11] [Impact Index Per Article: 1.8] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/21/2017] [Revised: 05/04/2018] [Accepted: 05/28/2018] [Indexed: 02/28/2024] Open
Abstract
PURPOSE To assess the impact of the ICRU report 90 recommendations on the beam-quality conversion factor, kQ , used for clinical reference dosimetry of megavoltage linac photon beams. METHODS The absorbed dose to water and the absorbed dose to the air in ionization chambers representative of those typically used for linac photon reference dosimetry are calculated at the reference depth in a water phantom using Monte Carlo simulations. Depth-dose calculations in water are also performed to investigate changes in beam quality specifiers. The calculations are performed in a cobalt-60 beam and MV photon beams with nominal energy between 6 MV and 25 MV using the EGSnrc simulation toolkit. Inputs to the calculations use stopping-power data for graphite and water from the original ICRU-37 report and the new proposed values from the recently published ICRU-90 report. Calculated kQ factors are compared using the two different recommendations for key dosimetry data and measured kQ factors. RESULTS Less than about 0.1% effects from ICRU-90 recommendations on the beam quality specifiers, the photon component of the percentage depth-dose at 10 cm, %dd(10)x , and the tissue-phantom ratio at 20 cm and 10 cm, TPR1020, are observed. Although using different recommendations for key dosimetric data impact water-to-air stopping-power ratios and ion chamber perturbation corrections by up to 0.54% and 0.40%, respectively, we observe little difference (≤0.14%) in calculated kQ factors. This is contradictory to the predictions in ICRU-90 that suggest differences up to 0.5% in high-energy photon beams. A slightly better agreement with experimental values is obtained when using ICRU-90 recommendations. CONCLUSION Users of the addendum to the TG-51 protocol for reference dosimetry of high-energy photon beams, which recommends Monte Carlo calculated kQ factors, can rest assured that the recommendations of ICRU report 90 on basic data have little impact on this central dosimetric parameter.
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Affiliation(s)
- Ernesto Mainegra-Hing
- Measurement Science and Standards, National Research Council of Canada, Ottawa, ON, K1A 0R6, Canada
| | - Bryan R Muir
- Measurement Science and Standards, National Research Council of Canada, Ottawa, ON, K1A 0R6, Canada
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Kinoshita N, Oguchi H, Adachi T, Shioura H, Kimura H. Uncertainty in positioning ion chamber at reference depth for various water phantoms. Rep Pract Oncol Radiother 2018; 23:199-206. [PMID: 29760594 PMCID: PMC5948320 DOI: 10.1016/j.rpor.2018.03.001] [Citation(s) in RCA: 4] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/24/2017] [Revised: 12/28/2017] [Accepted: 03/09/2018] [Indexed: 11/30/2022] Open
Abstract
BACKGROUND Uncertainty in the calibration of high-energy radiation sources is dependent on user and equipment type. AIM We evaluated the uncertainty in the positioning of a cylindrical chamber at a reference depth for reference dosimetry of high-energy photon beams and the resulting uncertainty in the chamber readings for 6- and 10-MV photon beams. The aim was to investigate major contributions to the positioning uncertainty to reduce the uncertainty in calibration for external photon beam radiotherapy. MATERIALS AND METHODS The following phantoms were used: DoseView 1D, WP1D, 1D SCANNER, and QWP-07 as one-dimensional (1D) phantoms for a vertical-beam geometry; GRI-7632 as a phantom for a fixed waterproofing sleeve; and PTW type 41023 and QWP-04 as 1D phantoms for a horizontal-beam geometry. The uncertainties were analyzed as per the Guide to the Expression of Uncertainty in Measurement. RESULTS The positioning and resultant uncertainties in chamber readings ranged from 0.22 to 0.35 mm and 0.12-0.25%, respectively, among the phantoms (using a coverage factor k = 1 in both cases). The major contributions to positioning uncertainty are: definition of the origin for phantoms among users for the 1D phantoms for a vertical-beam geometry, water level adjustment among users for the phantom for a fixed waterproofing sleeve, phantom window deformation, and non-water material of the window for the 1D phantoms for a horizontal-beam geometry. CONCLUSION The positioning and resultant uncertainties in chamber readings exhibited minor differences among the seven phantoms. The major components of these uncertainties differed among the phantom types investigated.
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Affiliation(s)
- Naoki Kinoshita
- Department of Radiological and Medical Laboratory Sciences, Nagoya University Graduate School of Medicine, Nagoya-shi, Aichi-ken 461-8673, Japan
- Radiological Center, University of Fukui Hospital, Yoshida-gun, Fukui-ken 910-1193, Japan
| | - Hiroshi Oguchi
- Department of Radiological and Medical Laboratory Sciences, Nagoya University Graduate School of Medicine, Nagoya-shi, Aichi-ken 461-8673, Japan
| | - Toshiki Adachi
- Radiological Center, University of Fukui Hospital, Yoshida-gun, Fukui-ken 910-1193, Japan
| | - Hiroki Shioura
- Department of Radiology, University of Fukui Hospital, Yoshida-gun, Fukui-ken 910-1193, Japan
| | - Hirohiko Kimura
- Department of Radiology, University of Fukui Hospital, Yoshida-gun, Fukui-ken 910-1193, Japan
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Eder H, Schlattl H. IEC 61331-1: A new setup for testing lead free X-ray protective clothing. Phys Med 2018; 45:6-11. [PMID: 29472092 DOI: 10.1016/j.ejmp.2017.11.015] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 09/22/2017] [Revised: 11/10/2017] [Accepted: 11/21/2017] [Indexed: 10/18/2022] Open
Abstract
PURPOSE Lead free protective clothing can create a higher part of secondary radiation (SR) than products that are based on lead. Hence, the attenuation properties may be downgraded. The international measuring standard IEC 61331-1:2014 declares the "inverse broad beam geometry" (IBG) as standard method, which has recently been modified to IBG∗ by the Physikalisch Technische Bundesanstalt (PTB). Because of the unspecific partial irradiation of the ionization chamber problems in the evaluation of lead equivalence values (LEVs) can occur. An alternative method proposed in this paper overcomes these problems. MATERIALS AND METHODS The alternative setup "modified broad beam geometry" (BBG∗) was tested and compared to the IBG∗ method by performing Monte Carlo simulations and radiation measurements including several lead-composite and lead-free protective materials. RESULTS Simulations show a reduced collection efficiency of SR under IBG∗ whereas BBG∗ features a high degree of SR collection. Material samples with a high amount of SR can feature up to 8% higher LEVs compared to IBG∗. For most of the currently salable materials the differences of BBG∗ vs IBG∗ amount to <3% (0.25 mm LEV) and <1% (0.50 mm LEV). In special cases the currently practiced method can lead to heavier protective clothings. CONCLUSIONS The proposed BBG∗ setup meets the specifications of the IEC standard with respect to energy response and SR collection. The method should be implemented in the IEC standard.
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Affiliation(s)
- Heinrich Eder
- Formerly Bavarian Environment Agency, Am Stadtpark 43, 81243 Munich, Germany.
| | - Helmut Schlattl
- Helmholtz Zentrum München, German Research Center for Environmental Health, Institute of Radiation Protection, Ingolstädter Landstrasse 1, 85764 Neuherberg, Germany.
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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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Renaud J, Sarfehnia A, Bancheri J, Seuntjens J. Aerrow: A probe-format graphite calorimeter for absolute dosimetry of high-energy photon beams in the clinical environment. Med Phys 2017; 45:414-428. [DOI: 10.1002/mp.12669] [Citation(s) in RCA: 17] [Impact Index Per Article: 2.4] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/07/2017] [Revised: 10/05/2017] [Accepted: 10/27/2017] [Indexed: 11/06/2022] Open
Affiliation(s)
- James Renaud
- Medical Physics Unit; McGill University; Montréal QC Canada
| | - Arman Sarfehnia
- Medical Physics Unit; McGill University; Montréal QC Canada
- Department of Radiation Oncology; University of Toronto; Toronto ON Canada
| | | | - Jan Seuntjens
- Medical Physics Unit; McGill University; Montréal QC Canada
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Christiansen E, Muir B, Belec J, Vandervoort E. Small composite field correction factors for the CyberKnife radiosurgery system: clinical and PCSR plans. Phys Med Biol 2017; 62:9240-9259. [PMID: 29058682 DOI: 10.1088/1361-6560/aa954c] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.1] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/31/2022]
Abstract
A formalism has been proposed for small and non-standard photon fields in which [Formula: see text] correction factors are used to correct dosimeter response in small fields (indiviual or composite) relative to that in a larger machine-specific reference (MSR) field. For clinical plans consisting of several fields, a plan-class specific reference (PCSR) plan can also be defined, serving as an intermediate calibration field between the MSR and clinical plans within a certain plan-class. In this work, the formalism was applied in the calculation of [Formula: see text] for 21 clinical plans delivered by the [Formula: see text] radiosurgery system, each plan employing one or two of the smallest diameter collimators: 5 mm, 7.5 mm, and 10 mm. Three detectors were considered: the Exradin A16 and A26 micro chambers, and the W1 plastic scintillator. The clinical plans were grouped into 7 plan-classes according to commonly shared characteristics. The suitability of using a PCSR plan to represent the detector response of each plan within the plan-class was investigated. Total and intermediate correction factors were calculated using the [Formula: see text] Monte Carlo user code. The corrections for the micro chambers were large, primarily due to the presence of the low-density air cavity and the volume averaging effect. The correction for the scintillator was found to be close to unity for most plans, indicating that this detector may be used to measure small clinical plan correction factors in any plan except for those using the 5 mm collimator. The PCSR plan was shown to be applicable to plan-classes comprising isocentric plans only, with plan-classes divided according to collimator size. For non-isocentric plans, the variation of [Formula: see text] as a function of the point of measurement within a single plan, as well as the high inter-plan-class variability of the correction factor, precludes the use of a PCSR plan.
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