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Rogers DWO. Minimum phantom size for megavoltage photon beam reference dosimetry. Med Phys 2024. [PMID: 38669481 DOI: 10.1002/mp.17099] [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: 12/14/2023] [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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McDermott PN. Monte Carlo evaluation of uncertainties in photon and electron TG-51 absorbed dose calibration. J Appl Clin Med Phys 2024:e14339. [PMID: 38608655 DOI: 10.1002/acm2.14339] [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: 06/21/2023] [Revised: 02/09/2024] [Accepted: 03/03/2024] [Indexed: 04/14/2024] Open
Abstract
PURPOSE The accuracy of dose delivery to all patients treated with medical linacs depends on the accuracy of beam calibration. Dose delivery cannot be any more accurate than this. Given the importance of this, it seems worthwhile taking another look at the expected uncertainty in TG-51 photon dose calibration and a first look at electron calibration. This work builds on the 2014 addendum to TG-51 for photons and adds to it by also considering electrons. In that publication, estimates were made of the uncertainty in the dose calibration. In this paper, we take a deeper look at this important issue. METHODS The methodology used here is more rigorous than previous determinations as it is based on Monte Carlo simulation of uncertainties. It is assumed that mechanical QA has been performed following TG-142 prior to beam calibration and that there are no uncertainties that exceed the tolerances specified by TG-142. RESULTS/CONCLUSIONS Despite the different methodology and assumptions, the estimated uncertainty in photon beam calibration is close to that in the addendum. The careful user should be able to easily reach a 95% confidence interval (CI) of ± 2.3% for photon beam calibration with standard instrumentation. For electron beams calibrated with a Farmer chamber, the estimated uncertainties are slightly larger, and the 95% CI is ±2.6% for 6 MeV and slightly smaller than this for 18 MeV. There is no clear energy dependence in these results. It is unlikely that the user will be able to improve on these uncertainties as the dominant factor in the uncertainty resides in the ion chamber dose calibration factorN D , w 60 Co $N_{D,w}^{{}^{60}{\mathrm{Co}}}$ . For both photons and electrons, reduction in the ion chamber depth uncertainty below about 0.5 mm and SSD uncertainty below 1 mm have almost no effect on the total dose uncertainty, as uncertainties beyond the user's control totally dominate under these circumstances.
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Affiliation(s)
- Patrick N McDermott
- Department of Radiation Oncology, William Beaumont University Hospital, Corewell Health, Royal Oak, Michigan, USA
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Nagake Y, Yasui K, Ooe H, Ichihara M, Iwase K, Toshito T, Hayashi N. Investigation of ionization chamber perturbation factors using proton beam and Fano cavity test for the Monte Carlo simulation code PHITS. Radiol Phys Technol 2024; 17:280-287. [PMID: 38261133 DOI: 10.1007/s12194-024-00777-y] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/02/2023] [Revised: 12/29/2023] [Accepted: 01/02/2024] [Indexed: 01/24/2024]
Abstract
The reference dose for clinical proton beam therapy is based on ionization chamber dosimetry. However, data on uncertainties in proton dosimetry are lacking, and multifaceted studies are required. Monte Carlo simulations are useful tools for calculating ionization chamber dosimetry in radiation fields and are sensitive to the transport algorithm parameters when particles are transported in a heterogeneous region. We aimed to evaluate the proton transport algorithm of the Particle and Heavy Ion Transport Code System (PHITS) using the Fano test. The response of the ionization chamber f Q and beam quality correction factors k Q were calculated using the same parameters as those in the Fano test and compared with those of other Monte Carlo codes for verification. The geometry of the Fano test consisted of a cylindrical gas-filled cavity sandwiched between two cylindrical walls. f Q was calculated as the ratio of the absorbed dose in water to the dose in the cavity in the chamber. We compared the f Q calculated using PHITS with that of a previous study, which was calculated using other Monte Carlo codes (Geant4, FULKA, and PENH) under similar conditions. The flight mesh, a parameter for charged particle transport, passed the Fano test within 0.15%. This was shown to be sufficiently accurate compared with that observed in previous studies. The f Q calculated using PHITS were 1.116 ± 0.002 and 1.124 ± 0.003 for NACP-02 and PTW-30013, respectively, and the k Q were 0.981 ± 0.008 and 1.027 ± 0.008, respectively, at 150 MeV. Our results indicate that PHITS can calculate the f Q and k Q with high precision.
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Affiliation(s)
- Yuya Nagake
- Graduate School of Health Sciences, Fujita Health University, Toyoake, Japan
| | - Keisuke Yasui
- School of Medical Sciences, Fujita Health University, Toyoake, Japan.
| | - Hiromu Ooe
- Graduate School of Health Sciences, Fujita Health University, Toyoake, Japan
| | | | - Kaito Iwase
- Graduate School of Health Sciences, Fujita Health University, Toyoake, Japan
| | - Toshiyuki Toshito
- Nagoya Proton Therapy Center, Nagoya City University West Medical Center, Nagoya, Japan
| | - Naoki Hayashi
- School of Medical Sciences, Fujita Health University, Toyoake, Japan
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Delbaere A, Younes T, Khamphan C, Vieillevigne L. Experimental validation of absorbed dose-to-medium calculation algorithms in heterogeneous media. Phys Med Biol 2024; 69:055006. [PMID: 38266285 DOI: 10.1088/1361-6560/ad222e] [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: 10/12/2023] [Accepted: 01/24/2024] [Indexed: 01/26/2024]
Abstract
Objective.The aim of this work was to determine heterogeneous correction factorshQclin,Qreffclin,frefdetm,wto validate absorbed dose-to-mediumDm,Qclinm,fclincalculation algorithms from detector readings. The impact of detector orientation perpendicular and parallel to the beam central axis on the correction factors was also investigated.Approach.ThehQclin,Qreffclin,frefdetm,wfactors were calculated for four types of detectors (PTW PinPoint T31016, PTW microDiamond T60019, PTW microSilicon T60023 and EBT3 film) placed in different media (cortical bone, lung, adipose tissue, Teflon and RW3) for the 6 MV energy beam with a 10 × 10 cm2field size. These corrections were then applied to the detector measurements performed at different depths in heterogeneous phantoms.Main results.ThehQclin,Qreffclin,frefdetm,wfactors mainly depended on the media and slightly on the type of detector. Considering all detectors, the largest corrections were found in high-density media with values ranging from 0.911 to 0.934 in cortical bone. For comparison, the corrections in other media were closer to unity with values from 0.966 (lung and RW3) to 0.991 (adipose tissue). Except for the PinPoint T31016, detector orientation-dependence was observed especially in high-density media. A good agreement (≤1.5%) was found betweenDm,Qclinm,fclincalculations and the detector readings corrected with thehQclin,Qreffclin,frefdetm,wfactor for all studied heterogeneous phantoms.Significance.This paper could serve as an initial guideline for medical physicists involved in the validation of the advanced type-b dose calculation algorithms reportingDm,Qclinm,fclin. To our knowledge, this is the first study to assess the impact of the orientation of different detectors in heterogeneous media. The orientation dependence of the detector response observed in water may not reflect what is observed in heterogeneous media, especially in high-density media. The knowledge of thehQclin,Qreffclin,frefdetm,wfactors becomes mandatory for accurate interpretation of detector readings and comparisons withDm,Qclinm,fclincalculations.
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Affiliation(s)
- Alexia Delbaere
- Department of Medical Physics, Oncopole Claudius Regaud - Institut Universitaire du Cancer de Toulouse, F-31059 Toulouse, France
- Centre de Recherches en Cancérologie de Toulouse, UMR1037 INSERM-Université Toulouse 3-ERL5294 CNRS, Oncopole, F-31037 Toulouse, France
| | - Tony Younes
- Department of Medical Physics, Oncopole Claudius Regaud - Institut Universitaire du Cancer de Toulouse, F-31059 Toulouse, France
- Centre de Recherches en Cancérologie de Toulouse, UMR1037 INSERM-Université Toulouse 3-ERL5294 CNRS, Oncopole, F-31037 Toulouse, France
| | - Catherine Khamphan
- Department of Medical Physics, Institut du Cancer-Avignon Provence, F-84000 Avignon, France
| | - Laure Vieillevigne
- Department of Medical Physics, Oncopole Claudius Regaud - Institut Universitaire du Cancer de Toulouse, F-31059 Toulouse, France
- Centre de Recherches en Cancérologie de Toulouse, UMR1037 INSERM-Université Toulouse 3-ERL5294 CNRS, Oncopole, F-31037 Toulouse, France
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Alissa M, Zink K, Röser A, Flatten V, Schoenfeld AA, Czarnecki D. Monte Carlo calculated beam quality correction factors for high energy electron beams. Phys Med 2024; 117:103179. [PMID: 38042061 DOI: 10.1016/j.ejmp.2023.103179] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 01/19/2023] [Revised: 10/05/2023] [Accepted: 11/16/2023] [Indexed: 12/04/2023] Open
Abstract
PURPOSE As the dosimetry protocol TRS 398 is being revised and the ICRU report 90 provides new recommendations for density correction as well as the mean ionization energies of water and graphite, updated beam quality correction factors kQ are calculated for reference dosimetry in electron beams and for independent validation of previously determined values. METHODS Monte Carlo simulations have been performed using EGSnrc to calculate the absorbed dose to water and the dose to the active volumes of ionization chambers SNC600c, SNC125c and SNC350p (all Sun Nuclear, A Mirion Medical Company, Melbourne, FL). Realistic clinical electron beam spectra were used to cover the entire energy range of therapeutic electron accelerators. The Monte Carlo simulations were validated by measurements on a clinical linear accelerator. With regards to the cylindrical chambers, the simulations were performed according to the setup recommendations of TRS 398 and AAPM TG 51, i.e. with and without consideration of a reference point shift by rcav/2. RESULTS kQ values as a function of the respective beam quality specifier R50 were fitted by recommended equations for electron beam dosimetry in the range of 5 MeV to 18 MeV. The fitting curves to the calculated values showed a root mean square deviation between 0.0016 and 0.0024. CONCLUSION Electron beam quality correction factors kQ were calculated by Monte Carlo simulations for the cylindrical ionization chambers SNC600c and SNC125c as well as the plane parallel ionization chamber SNC350p to provide updated data for the TRS 398 and TG 51 dosimetry protocols.
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Affiliation(s)
- Mohamad Alissa
- Institute of Medical Physics and Radiation Protection, University of Applied Sciences Giessen (THM), Wiesenstraße 14, Giessen, 35390, Germany
| | - Klemens Zink
- Institute of Medical Physics and Radiation Protection, University of Applied Sciences Giessen (THM), Wiesenstraße 14, Giessen, 35390, Germany; Department of Radiotherapy and Radiation Oncology, University Medical Center Giessen and Marburg, Baldingerstraße, Marburg, 35043, Germany
| | - Arnd Röser
- Helios Universitätsklinikum Wuppertal, Heusnerstraße 40, Wuppertal, 42283, Germany
| | - Veronika Flatten
- Sun Nuclear, A Mirion Medical Company, 3275 Suntree Blvd, Melbourne, 32940, FL, USA
| | - Andreas A Schoenfeld
- Sun Nuclear, A Mirion Medical Company, 3275 Suntree Blvd, Melbourne, 32940, FL, USA
| | - Damian Czarnecki
- Institute of Medical Physics and Radiation Protection, University of Applied Sciences Giessen (THM), Wiesenstraße 14, Giessen, 35390, Germany.
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Mahfirotin DA, Ferliano B, Handika AD, Asril YS, Fadli M, Ryangga D, Nelly N, Kurniawan E, Wibowo WE, Yadav P, Pawiro SA. A multicenter study of modified electron beam output calibration. J Appl Clin Med Phys 2024; 25:e14232. [PMID: 38088260 PMCID: PMC10795448 DOI: 10.1002/acm2.14232] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/28/2023] [Revised: 11/13/2023] [Accepted: 11/19/2023] [Indexed: 01/19/2024] Open
Abstract
PURPOSE This study aims to assess the accuracy of a modified electron beam calibration based on the IAEA TRS-398 and AAPM-TG-51 in multicenter radiotherapy. METHODS This study was performed using the Elekta and Varian Linear Accelerator electron beams with energies of 4-22 MeV under reference conditions using cylindrical (PTW 30013, IBA FC65-G, and IBA FC65-P) and parallel-plate (PTW 34045, PTW 34001, and IBA PPC-40) chambers. The modified calibration used a cylindrical chamber and an updatedk ' Q $k{^{\prime}}_Q$ based on Monte Carlo calculations, whereas TRS-398 and TG-51 used cylindrical and parallel-plate chambers for reference dosimetry. The dose ratio of the modified calibration procedure, TRS-398 and TG-51 were obtained by comparing the dose at the maximum depth of the modified calibration to TRS-398 and TG-51. RESULTS The study found that all cylindrical chambers' beam quality conversion factors determined with the modified calibration( k ' Q ) $( {{{k^{\prime}}}_Q} )$ to the TRS-398 and TG-51 vary from 0.994 to 1.003 and 1.000 to 1.010, respectively. The dose ratio of modified/TRS-398cyl and modified/TRS-398parallel-plate, the variation ranges were 0.980-1.014 and 0.981-1.019, while for the counterpart modified/TG-51cyl was found varying between 0.991 and 1.017 and the ratio of modified/TG-51parallel-plate varied in the range of 0.981-1.019. CONCLUSION This multi-institutional study analyzed a modified calibration procedure utilizing new data for electron beam calibrations at multiple institutions and evaluated existing calibration protocols. Based on observed variations, the current calibration protocols should be updated with detailed metrics on the stability of linac components.
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Affiliation(s)
- Dwi Aprilia Mahfirotin
- Department of PhysicsFaculty of Mathematics and Natural SciencesUniversitas Indonesia, DepokWest JavaIndonesia
- Department of Radiation OncologyMitra Keluarga Bekasi Timur Hospital, BekasiWest JavaIndonesia
| | - Brian Ferliano
- Department of Radiation OncologyGading Pluit HospitalJakartaIndonesia
| | - Andrian Dede Handika
- Department of Radiation OncologyPersahabatan Central General HospitalJakartaIndonesia
| | - Yosi Sudarsi Asril
- Department of Radiation OncologyMayapada Hospital Jakarta SelatanJakartaIndonesia
| | - Muhamad Fadli
- Department of Radiation OncologyMRCCC Siloam Hospital SemanggiJakartaIndonesia
| | - Dea Ryangga
- Department of Radiation OncologyPasar Minggu Regional HospitalJakartaIndonesia
| | - Nelly Nelly
- Department of Radiation OncologySiloam Hospital TB SimatupangJakartaIndonesia
| | - Eddy Kurniawan
- Department of Radiation OncologyTzu Chi HospitalJakartaIndonesia
| | - Wahyu Edy Wibowo
- Department of Radiation OncologyDr. Cipto Mangunkusumo National General Hospital CentralFaculty of MedicineUniversitas IndonesiaJakartaIndonesia
| | - Poonam Yadav
- Department of Radiation OncologyNorthwestern Memorial HospitalNorthwestern University Feinberg School of MedicineChicagoIllinoisUSA
| | - Supriyanto Ardjo Pawiro
- Department of PhysicsFaculty of Mathematics and Natural SciencesUniversitas Indonesia, DepokWest JavaIndonesia
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Baumann KS, Derksen L, Witt M, Adeberg S, Zink K. The influence of different versions of FLUKA and GEANT4 on the calculation of response functions of ionization chambers in clinical proton beams. Phys Med Biol 2023; 68:24NT01. [PMID: 37939402 DOI: 10.1088/1361-6560/ad0ad4] [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: 07/23/2023] [Accepted: 11/08/2023] [Indexed: 11/10/2023]
Abstract
Objective.To investigate the influence of different versions of the Monte Carlo codesgeant4 andflukaon the calculation of overall response functionsfQof air-filled ionization chambers in clinical proton beams.Approach. fQfactors were calculated for six plane-parallel and four cylindrical ionization chambers withgeant4 andfluka. These factors were compared to already published values that were derived using older versions of these codes.Main results.Differences infQfactors calculated with different versions of the same Monte Carlo code can be up to ∼1%. Especially forgeant4, the updated version leads to a more pronounced dependence offQon proton energy and to smallerfQfactors for high energies.Significance.Different versions of the same Monte Carlo code can lead to differences in the calculation offQfactors of up to ∼1% without changing the simulation setup, transport parameters, ionization chamber geometry modeling, or employed physics lists. These findings support the statement that the dominant contributor to the overall uncertainty of Monte Carlo calculatedfQfactors are type-B uncertainties.
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Affiliation(s)
- Kilian-Simon Baumann
- University Medical Center Giessen-Marburg, Department of Radiotherapy and Radiooncology, Marburg, Germany
- University of Applied Sciences, Institute of Medical Physics and Radiation Protection, Giessen, Germany
- Marburg Ion-Beam Therapy Center (MIT), Marburg, Germany
| | - Larissa Derksen
- University of Applied Sciences, Institute of Medical Physics and Radiation Protection, Giessen, Germany
| | - Matthias Witt
- University of Applied Sciences, Institute of Medical Physics and Radiation Protection, Giessen, Germany
- Marburg Ion-Beam Therapy Center (MIT), Marburg, Germany
| | - Sebastian Adeberg
- University Medical Center Giessen-Marburg, Department of Radiotherapy and Radiooncology, Marburg, Germany
- Marburg Ion-Beam Therapy Center (MIT), Marburg, Germany
- Universitäres Centrum für Tumorerkrankungen (UCT) Frankfurt - Marburg, Germany
| | - Klemens Zink
- University Medical Center Giessen-Marburg, Department of Radiotherapy and Radiooncology, Marburg, Germany
- University of Applied Sciences, Institute of Medical Physics and Radiation Protection, Giessen, Germany
- Marburg Ion-Beam Therapy Center (MIT), Marburg, Germany
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Iakovenko V, Keller B, Malkov VN, Sahgal A, Sarfehnia A. Quantifying uncertainties associated with reference dosimetry in an MR-Linac. J Appl Clin Med Phys 2023; 24:e14087. [PMID: 37354202 PMCID: PMC10647966 DOI: 10.1002/acm2.14087] [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: 03/02/2023] [Revised: 05/19/2023] [Accepted: 05/23/2023] [Indexed: 06/26/2023] Open
Abstract
BACKGROUND Magnetic resonance (MR)-guided radiation therapy provides capabilities to utilize high-resolution and real-time MR imaging before and during treatment, which is critical for adaptive radiotherapy. This emerging modality has been promptly adopted in the clinic settings in advance of adaptations to reference dosimetry formalism that are needed to account for the presence of strong magnetic fields. In particular, the influence of magnetic field on the uncertainty of parameters in the reference dosimetry equation needs to be determined in order to fully characterize the uncertainty budget for reference dosimetry in MR-guided radiation therapy systems. PURPOSE To identify and quantify key sources of uncertainty in the reference dosimetry of external high energy radiotherapy beams in the presence of a strong magnetic field. METHODS In the absence of a formalized Task Group report for reference dosimetry in MR-integrated linacs, the currently suggested formalism follows the TG-51 protocol with the addition of a quality conversion factor kBQ accounting for the effects of the magnetic field on ionization chamber response. In this work, we quantify various sources of uncertainty that impact each of the parameters in the formalism, and evaluate their overall contribution to the final dose. Measurements are done in a 1.5 T MR-Linac (Unity, Elekta AB, Stockholm, Sweden) which integrates a 1.5 T Philips MR scanner and a 7 MVFFF linac. The responses of several reference-class small volume ionization chambers (Exradin:A1SL, IBA:CC13, PTW:Semiflex-3D) and Farmer type ionization chambers (Exradin:A19, IBA:FC65-G) were evaluated throughout this process. Long-term reproducibility and stability of beam quality,TPR 10 20 ${\mathrm{TPR}}_{10}^{20}$ , was also measured with an in-house built phantom. RESULTS Relative to the conventional external high energy linacs, the uncertainty on overall reference dose in MR-linac is more significantly affected by the chamber setup: A translational displacement along y-axis of ± 3 mm results in dose variation of < |0.20| ± 0.02% (k = 1), while rotation of ± 5° in horizontal and vertical parallel planes relative to relative to the direction of magnetic field, did not exceed variation of < |0.44| ± 0.02% for all 5 ionization chambers. We measured a larger dose variation for xy-plane (horizontal) rotations (< |0.44| ± 0.02% (k = 1)) than for yz-plane (vertical) rotations (< ||0.28| ± 0.02% (k = 1)), which we associate with the gradient of kB,Q as a function of chamber orientation with respect to direction of the B0 -field. Uncertainty in Pion (for two depths), Ppol (with various sub-studies including effects of cable length, cable looping in the MRgRT bore, connector type in magnetic environment), and Prp were determined. Combined conversion factor kQ × kB,Q was provided for two reference depths at four cardinal angle orientations. Over a two-year period, beam quality was quite stable withTPR 10 20 ${\mathrm{TPR}}_{10}^{20}$ being 0.669 ± 0.01%. The actual magnitude ofTPR 10 20 ${\mathrm{TPR}}_{10}^{20}$ was measured using identical equipment and compared between two different Elekta Unity MR-Linacs with results agreeing to within 0.21%. CONCLUSION In this work, the uncertainty of a number of parameters influencing reference dosimetry was quantified. The results of this work can be used to identify best practice guidelines for reference dosimetry in the presence of magnetic fields, and to evaluate an uncertainty budget for future reference dosimetry protocols for MR-linac.
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Affiliation(s)
- Viktor Iakovenko
- Division of Medical Physics and EngineeringDepartment of Radiation OncologyUniversity of Texas Southwestern Medical CenterDallasTexasUSA
| | - Brian Keller
- Department of Radiation OncologySunnybrook Health Sciences CentreUniversity of TorontoTorontoOntarioCanada
| | | | - Arjun Sahgal
- Department of Radiation OncologySunnybrook Health Sciences CentreUniversity of TorontoTorontoOntarioCanada
| | - Arman Sarfehnia
- Department of Radiation OncologySunnybrook Health Sciences CentreUniversity of TorontoTorontoOntarioCanada
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Urago Y, Sakama M, Sakata D, Fukuda S, Katayose T, Chang W. Monte Carlo-calculated beam quality and perturbation correction factors validated against experiments for Farmer and Markus type ionization chambers in therapeutic carbon-ion beams. Phys Med Biol 2023; 68:185013. [PMID: 37579752 DOI: 10.1088/1361-6560/acf024] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/14/2023] [Accepted: 08/14/2023] [Indexed: 08/16/2023]
Abstract
Objective. In current dosimetry protocols, the estimated uncertainty of the measured absorbed dose to waterDwin carbon-ion beams is approximately 3%. This large uncertainty is mainly contributed by the standard uncertainty of the beam quality correction factorkQ. In this study, thekQvalues in four cylindrical chambers and two plane-parallel chambers were calculated using Monte Carlo (MC) simulations in the plateau region. The chamber-specific perturbation correction factorPof each chamber was also determined through MC simulations.Approach.kQfor each chamber was calculated using MC code Geant4. The simulatedkQratios in subjected chambers and reference chambers were validated through comparisons against our measured values. In the measurements in Heavy-Ion Medical Accelerator in Chiba,kQratios were obtained fromDwvalues of60Co, 290- and 400 MeV u-1carbon-ion beams that were measured with the subjected ionization chamber and the reference chamber. In the simulations,fQ(the product of the water-to-air stopping power ratio andP) was acquired fromDwand the absorbed dose to air calculated in the sensitive volume of each chamber.kQvalues were then calculated from the simulatedfQand the literature-extractedWairand compared with previous publications.Main results. The calculatedkQratios in the subjected chambers to the reference chamber agreed well with the measuredkQratios. ThekQuncertainty was reduced from the current recommendation of approximately 3% to 1.7%. ThePvalues were close to unity in the cylindrical chambers and nearly 1% above unity in the plane-parallel chambers.Significance. ThekQvalues of carbon-ion beams were accurately calculated in MC simulations and thekQratios were validated through ionization chamber measurements. The results indicate a need for updating the current recommendations, which assume a constantPof unity in carbon-ion beams, to recommendations that consider chamber-induced differences.
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Affiliation(s)
- Yuka Urago
- Department of Radiological Science, Graduate School of Human Health Science, Tokyo Metropolitan University, Tokyo, Japan
- QST Hospital, National Institutes for Quantum Science and Technology, Chiba, Japan
| | - Makoto Sakama
- QST Hospital, National Institutes for Quantum Science and Technology, Chiba, Japan
| | | | - Shigekazu Fukuda
- QST Hospital, National Institutes for Quantum Science and Technology, Chiba, Japan
| | | | - Weishan Chang
- Department of Radiological Science, Graduate School of Human Health Science, Tokyo Metropolitan University, Tokyo, Japan
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10
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Baumann KS, Gomà C, Wulff J, Kretschmer J, Zink K. Monte Carlo calculated ionization chamber correction factors in clinical proton beams - deriving uncertainties from published data. Phys Med 2023; 113:102655. [PMID: 37603909 DOI: 10.1016/j.ejmp.2023.102655] [Citation(s) in RCA: 1] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 12/15/2022] [Revised: 06/16/2023] [Accepted: 08/05/2023] [Indexed: 08/23/2023] Open
Abstract
For the update of the IAEA TRS-398 Code of Practice (CoP), global ionization chamber factors (fQ) and beam quality correction factors (kQ) for air-filled ionization chambers in clinical proton beams have been calculated with different Monte Carlo codes. In this study, average Monte Carlo calculated fQ and kQ factors are provided and the uncertainty of these factors is estimated. Average fQ factors in monoenergetic proton beams with energies between 60 MeV and 250 MeV were derived from Monte Carlo calculated fQ factors published in the literature. Altogether, 195 fQ factors for six plane-parallel and three cylindrical ionization chambers calculated with penh, fluka and geant4 were incorporated. Additionally, a weighted standard deviation of fQ factors was calculated, where the same weight was assigned to each Monte Carlo code. From average fQ factors, kQ factors were derived and compared to the values from the IAEA TRS-398 CoP published in 2000 as well as to the values of the upcoming version. Average Monte Carlo calculated fQ factors are constant within 0.6% over the energy range investigated. In general, the different Monte Carlo codes agree within 1% for low energies and show larger differences up to 2% for high energies. As a result, the standard deviation of fQ factors increases with energy and is ∼0.3% for low energies and ∼0.8% for high energies. kQ factors derived from average Monte Carlo calculated fQ factors differ from the values presented in the IAEA TRS-398 CoP by up to 2.4%. The overall estimated uncertainty of Monte Carlo calculated kQ factors is ∼0.5%-1% smaller than the uncertainties estimated in IAEA TRS-398 CoP since the individual ionization chamber characteristics (e.g. fluence perturbations) are considered in detail in Monte Carlo calculations. The agreement between Monte Carlo calculated kQ factors and the values of the upcoming version of IAEA TRS-398 CoP is better with deviations smaller than 1%.
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Affiliation(s)
- Kilian-Simon Baumann
- University Medical Center Giessen-Marburg, Department of Radiotherapy and Radiooncology, Marburg, Germany; University of Applied Sciences, Institute of Medical Physics and Radiation Protection, Giessen, Germany; Marburg Ion-Beam Therapy Center, Marburg, Germany.
| | - Carles Gomà
- Hospital Clínic de Barcelona, Department of Radiation Oncology, Barcelona, Spain
| | - Jörg Wulff
- West German Proton Therapy Center (WPE), Essen, Germany
| | - Jana Kretschmer
- Carl-von-Ossietzky University, University Clinic for Medical Radiation Physics, Medical Campus Pius Hospital, Oldenburg, Germany; Department of Radiation Oncology, University Medical Center Groningen, University of Groningen, The Netherlands
| | - Klemens Zink
- University Medical Center Giessen-Marburg, Department of Radiotherapy and Radiooncology, Marburg, Germany; University of Applied Sciences, Institute of Medical Physics and Radiation Protection, Giessen, Germany; Marburg Ion-Beam Therapy Center, Marburg, Germany
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11
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Begg J, Jelen U, Moutrie Z, Oliver C, Holloway L, Brown R. ACPSEM position paper: dosimetry for magnetic resonance imaging linear accelerators. Phys Eng Sci Med 2023; 46:1-17. [PMID: 36806156 PMCID: PMC10030536 DOI: 10.1007/s13246-023-01223-w] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Accepted: 01/19/2023] [Indexed: 02/23/2023]
Abstract
Consistency and clear guidelines on dosimetry are essential for accurate and precise dosimetry, to ensure the best patient outcomes and to allow direct dose comparison across different centres. Magnetic Resonance Imaging Linac (MRI-linac) systems have recently been introduced to Australasian clinics. This report provides recommendations on reference dosimetry measurements for MRI-linacs on behalf of the Australiasian College of Physical Scientists and Engineers in Medicine (ACPSEM) MRI-linac working group. There are two configurations considered for MRI-linacs, perpendicular and parallel, referring to the relative direction of the magnetic field and radiation beam, with different impacts on dose deposition in a medium. These recommendations focus on ion chambers which are most commonly used in the clinic for reference dosimetry. Water phantoms must be MR safe or conditional and practical limitations on phantom set-up must be considered. Solid phantoms are not advised for reference dosimetry. For reference dosimetry, IAEA TRS-398 recommendations cannot be followed completely due to physical differences between conventional linac and MRI-linac systems. Manufacturers' advice on reference conditions should be followed. Beam quality specification of TPR20,10 is recommended. The configuration of the central axis of the ion chamber relative to the magnetic field and radiation beam impacts the chamber response and must be considered carefully. Recommended corrections to delivered dose are [Formula: see text], a correction for beam quality and [Formula: see text], for the impact of the magnetic field on dosimeter response in the magnetic field. Literature based values for [Formula: see text] are given. It is important to note that this is a developing field and these recommendations should be used together with a review of current literature.
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Affiliation(s)
- Jarrad Begg
- Department of Medical Physics, Liverpool and Macarthur Cancer Therapy Centre, Liverpool, NSW, 2170, Australia.
- Ingham Institute for Applied Medical Research, Liverpool, NSW, 2170, Australia.
- South Western Sydney Clinical School, University of New South Wales, Liverpool, NSW, 2170, Australia.
| | - Urszula Jelen
- St Vincents Clinic, GenesisCare, Darlinghurst, NSW, 2010, Australia
| | - Zoe Moutrie
- Department of Medical Physics, Liverpool and Macarthur Cancer Therapy Centre, Liverpool, NSW, 2170, Australia
| | - Chris Oliver
- Primary Standards Dosimetry Laboratory, Australian Radiation Protection and Nuclear Safety Agency, Yallambie, VIC, 3085, Australia
| | - Lois Holloway
- Department of Medical Physics, Liverpool and Macarthur Cancer Therapy Centre, Liverpool, NSW, 2170, Australia
- Ingham Institute for Applied Medical Research, Liverpool, NSW, 2170, Australia
- South Western Sydney Clinical School, University of New South Wales, Liverpool, NSW, 2170, Australia
- Centre for Medical Radiation Physics, University of Wollongong, Wollongong, NSW, 2522, Australia
- Institute of Medical Physics, University of Sydney, Camperdown, NSW, 2505, Australia
| | - Rhonda Brown
- Australian Clinical Dosimetry Service, Australian Radiation Protection and Nuclear Safety Agency, Yallambie, VIC, 3085, Australia
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12
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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: 0] [Impact Index Per Article: 0] [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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13
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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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14
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Palmans H, Lourenço A, Medin J, Vatnitsky S, Andreo P. Current best estimates of beam quality correction factors for reference dosimetry of clinical proton beams. Phys Med Biol 2022; 67. [DOI: 10.1088/1361-6560/ac9172] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/22/2022] [Accepted: 09/12/2022] [Indexed: 11/12/2022]
Abstract
Abstract
Objective. To review the currently available data on beam quality correction factors,
k
Q
,
for ionization chambers in clinical proton beams and derive their current best estimates for the updated recommendations of the IAEA TRS-398 Code of Practice. Approach. The reviewed data come from 20 publications from which
k
Q
values can be derived either directly from calorimeter measurements, indirectly from comparison with other chambers or from Monte Carlo calculated overall chamber factors,
f
Q
.
For cylindrical ionization chambers, a distinction is made between data obtained in the centre of a spread-out Bragg peak and those obtained in the plateau region of single-energy fields. For the latter, the effect of depth dose gradients has to be considered. To this end an empirical model for previously published displacement correction factors for single-layer scanned beams was established, while for unmodulated scattered beams experimental data were used. From all the data, chamber factors,
f
Q
,
and chamber perturbation correction factors,
p
Q
,
were then derived and analysed. Main results. The analysis showed that except for the beam quality dependence of the water-to-air mass stopping power ratio and, for cylindrical ionization chambers in unmodulated beams, of the displacement correction factor, there is no remaining beam quality dependence of the chamber perturbation correction factors
p
Q
.
Based on this approach, average values of the beam quality independent part of the perturbation factors were derived to calculate
k
Q
values consistent with the data in the literature. Significance. The resulting data from this analysis are current best estimates of
k
Q
values for modulated scattered beams and single-layer scanned beams used in proton therapy. Based on this, a single set of harmonized values is derived to be recommended in the update of IAEA TRS-398.
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15
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Failing T, Hartmann GH, Hensley FW, Keil B, Zink K. Enhancement of the EGSnrc code egs_chamber for fast fluence calculations of charged particles. Z Med Phys 2022; 32:417-427. [PMID: 35643800 PMCID: PMC9948836 DOI: 10.1016/j.zemedi.2022.04.003] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/06/2022] [Revised: 03/29/2022] [Accepted: 04/14/2022] [Indexed: 11/19/2022]
Abstract
PURPOSE Simulation of absorbed dose deposition in a detector is one of the key tasks of Monte Carlo (MC) dosimetry methodology. Recent publications (Hartmann and Zink, 2018; Hartmann and Zink, 2019; Hartmann et al., 2021) have shown that knowledge of the charged particle fluence differential in energy contributing to absorbed dose is useful to provide enhanced insight on how response depends on detector properties. While some EGSnrc MC codes provide output of charged particle spectra, they are often restricted in setup options or limited in calculation efficiency. For detector simulations, a promising approach is to upgrade the EGSnrc code egs_chamber which so far does not offer charged particle calculations. METHODS Since the user code cavity offers charged particle fluence calculation, the underlying algorithm was embedded in egs_chamber. The modified code was tested against two EGSnrc applications and DOSXYZnrc which was modified accordingly by one of the authors. Furthermore, the gain in efficiency achieved by photon cross section enhancement was determined quantitatively. RESULTS Electron and positron fluence spectra and restricted cema calculated by egs_chamber agreed well with the compared applications thus demonstrating the feasibility of the new code. Additionally, variance reduction techniques are now applicable also for fluence calculations. Depending on the simulation setup, considerable gains in efficiency were obtained by photon cross section enhancement. CONCLUSION The enhanced egs_chamber code represents a valuable tool to investigate the response of detectors with respect to absorbed dose and fluence distribution and the perturbation caused by the detector in a reasonable computation time. By using intermediate phase space scoring, egs_chamber offers parallel calculation of charged particle fluence spectra for different detector configurations in one single run.
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Affiliation(s)
- Thomas Failing
- Department for Radiotherapy and Radiooncology, University Medical Center Göttingen, Göttingen 37075, Germany; Institute of Medical Physics and Radiation Protection (IMPS), University of Applied Sciences, Gießen 35390, Germany.
| | | | - Frank W Hensley
- Department for Radiotherapy and Radiooncology, University Medical Center Heidelberg, Heidelberg 69120, Germany
| | - Boris Keil
- Institute of Medical Physics and Radiation Protection (IMPS), University of Applied Sciences, Gießen 35390, Germany; Diagnostic and Interventional Radiology, Philipps-University Marburg, Marburg 35043, Germany
| | - Klemens Zink
- Institute of Medical Physics and Radiation Protection (IMPS), University of Applied Sciences, Gießen 35390, Germany; Department for Radiotherapy and Radiooncology, University Medical Center Giessen-Marburg, Marburg 35043, Germany; Marburg Iontherapy Center (MIT), Marburg 35043, Germany
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16
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Yano M, Araki F, Ohno T. Monte Carlo study of small-field dosimetry for an ELEKTA Unity MR-Linac system. Radiat Phys Chem Oxf Engl 1993 2022. [DOI: 10.1016/j.radphyschem.2022.110036] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/16/2023]
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17
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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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18
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Shariff M, Stillkrieg W, Lotter M, Lohmann D, Weissmann T, Fietkau R, Bert C. Dosimetry, Optimization and FMEA of Total Skin Electron Irradiation (TSEI). Z Med Phys 2021; 32:228-239. [PMID: 34740500 PMCID: PMC9948874 DOI: 10.1016/j.zemedi.2021.09.004] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/05/2021] [Revised: 09/20/2021] [Accepted: 09/25/2021] [Indexed: 10/19/2022]
Abstract
PURPOSE Total Skin Electron Irradiation (TSEI) is a method for treating malignant cutaneous T-cell lymphomas. This work aims to implement and optimize the total skin technique established at Strahlenklinik Erlangen, Germany on two new linear accelerators and to quantify the risks using failure mode and effects (FMEA) analysis. MATERIAL AND METHODS TSEI is performed at a VersaHD accelerator (Elekta, Stockholm) with 6MeV in the "high dose rate mode" HDRE and a nominal field size of 40×40cm2. To reach the entire skin surface, the patients perform 6 different body positions at a distance of 330cm behind an acrylic scatter plate, with two overlapping irradiation fields being radiated at 2 gantry angles per position. The irradiation technique was commissioned according to the recommendation of AAPM report 23. With the help of a reference profile at 270°, 2 gantry angles were calculated, which in total resulted in an optimal dose distribution. This was metrologically verified with ion-chamber measurements in the patient's longitudinal axis. The influence of the shape of the acrylic scatter plate and the distance between the acrylic scatter plate and patient was determined by measurements. The dose homogeneity was verified using an anthropomorphic disc phantom equipped with GafChromic films. The workflows and failure modes of the total skin technique were described in a process map and subsequently quantified with a FMEA analysis. RESULTS An optimal dose distribution is achieved at a distance of SSD=330cm, using the gantry angles 289° and 251°. The previously used segmented acrylic scatter plate was replaced by a flat plate (200×120×0.5cm3), which is placed at a distance of 50cm in front of the patient. The densitometric evaluation of the GafChromic films in the anthropomorphic disc phantom revealed an expected dose distribution of 3Gy at a depth of up to 1.5cm below the skin surface, with a homogeneity of ±10% over the phantom's longitudinal axis. By FMEA a maximum risk priority number of 30 was determined. CONCLUSION Based on the calculations and measurements performed on the new accelerators as well as the risk analysis, we concluded that total skin therapy can be implemented clinically.
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Affiliation(s)
- Maya Shariff
- Department of Radiation Oncology, Universitätsklinikum Erlangen, Friedrich-Alexander-Universität Erlangen-Nürnberg, Universitätsstraße 27, 91054, Erlangen, Germany; Comprehensive Cancer Center Erlangen-EMN (CCC ER-EMN), Erlangen, Germany.
| | - Willi Stillkrieg
- Department of Radiation Oncology, Universitätsklinikum Erlangen, Friedrich-Alexander-Universität Erlangen-Nürnberg, Universitätsstraße 27, 91054, Erlangen, Germany,Comprehensive Cancer Center Erlangen-EMN (CCC ER-EMN), Erlangen, Germany
| | - Michael Lotter
- Department of Radiation Oncology, Universitätsklinikum Erlangen, Friedrich-Alexander-Universität Erlangen-Nürnberg, Universitätsstraße 27, 91054, Erlangen, Germany,Comprehensive Cancer Center Erlangen-EMN (CCC ER-EMN), Erlangen, Germany
| | - Daniel Lohmann
- Department of Radiation Oncology, Universitätsklinikum Erlangen, Friedrich-Alexander-Universität Erlangen-Nürnberg, Universitätsstraße 27, 91054, Erlangen, Germany,Comprehensive Cancer Center Erlangen-EMN (CCC ER-EMN), Erlangen, Germany
| | - Thomas Weissmann
- Department of Radiation Oncology, Universitätsklinikum Erlangen, Friedrich-Alexander-Universität Erlangen-Nürnberg, Universitätsstraße 27, 91054, Erlangen, Germany,Comprehensive Cancer Center Erlangen-EMN (CCC ER-EMN), Erlangen, Germany
| | - Rainer Fietkau
- Department of Radiation Oncology, Universitätsklinikum Erlangen, Friedrich-Alexander-Universität Erlangen-Nürnberg, Universitätsstraße 27, 91054, Erlangen, Germany,Comprehensive Cancer Center Erlangen-EMN (CCC ER-EMN), Erlangen, Germany
| | - Christoph Bert
- Department of Radiation Oncology, Universitätsklinikum Erlangen, Friedrich-Alexander-Universität Erlangen-Nürnberg, Universitätsstraße 27, 91054, Erlangen, Germany,Comprehensive Cancer Center Erlangen-EMN (CCC ER-EMN), Erlangen, Germany
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19
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Hartmann GH, Andreo P, Kapsch RP, Zink K. Cema-based formalism for the determination of absorbed dose for high-energy photon beams. Med Phys 2021; 48:7461-7475. [PMID: 34613620 DOI: 10.1002/mp.15266] [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: 01/18/2021] [Revised: 07/26/2021] [Accepted: 09/23/2021] [Indexed: 11/08/2022] Open
Abstract
PURPOSE Determination of absorbed dose is well established in many dosimetry protocols and considered to be highly reliable using ionization chambers under reference conditions. If dosimetry is performed under other conditions or using other detectors, however, open questions still remain. Such questions frequently refer to appropriate correction factors. A converted energy per mass (cema)-based approach to formulate such correction factors offers a good understanding of the specific response of a detector for dosimetry under various measuring conditions and thus an estimate of pros and cons of its application. METHODS Determination of absorbed dose requires the knowledge of the beam quality correction factor kQ,Qo , where Q denotes the quality of a user beam and Qo is the quality of the radiation used for calibration. In modern Monte Carlo (MC)-based methods, kQ,Qo is directly derived from the MC-calculated dose conversion factor, which is the ratio between the absorbed dose at a point of interest in water and the mean absorbed dose in the sensitive volume of an ion chamber. In this work, absorbed dose is approximated by the fundamental quantity cema. This approximation allows the dose conversion factor to be substituted by the cema conversion factor. Subsequently, this factor is decomposed into a product of cema ratios. They are identified as the stopping power ratio water to the material in the sensitive detector volume, and as the correction factor for the fluence perturbation of the secondary charged particles in the detector cavity caused by the presence of the detector. This correction factor is further decomposed with respect to the perturbation caused by the detector cavity and that caused by external detector properties. The cema-based formalism was subsequently tested by MC calculations of the spectral fluence of the secondary charged particles (electrons and positrons) under various conditions. RESULTS MC calculations demonstrate that considerable fluence perturbation may occur particularly under non-reference conditions. Cema-based correction factors to be applied in a 6-MV beam were obtained for a number of ionization chambers and for three solid-state detectors. Feasibility was shown at field sizes of 4 × 4 and 0.5 cm × 0.5 cm. Values of the cema ratios resulting from the decomposition of the dose conversion factor can be well correlated with detector response. Under the small field conditions, the internal fluence correction factor of ionization chambers is considerably dependent on volume averaging and thus on the shape and size of the cavity volume. CONCLUSIONS The cema approach is particularly useful at non-reference conditions including when solid-state detectors are used. Perturbation correction factors can be expressed and evaluated by cema ratios in a comprehensive manner. The cema approach can serve to understand the specific response of a detector for dosimetry to be dependent on (a) radiation quality, (b) detector properties, and (c) electron fluence changes caused by the detector. This understanding may also help to decide which detector is best suited for a specific measurement situation.
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Affiliation(s)
- Günther H Hartmann
- Division of Medical Physics in Radiation Oncology, German Cancer Research Center (DKFZ), Heidelberg, Germany
| | - Pedro Andreo
- Department of Medical Radiation Physics and Nuclear Medicine, Karolinska University Hospital, Stockholm, Sweden.,Department of Oncology-Pathology, Karolinska Institutet, Stockholm, Sweden
| | | | - Klemens Zink
- Institut fuer Medizinische Physik und Strahlenschutz (IMPS), University of Applied Sciences, Giessen, Giessen, Germany.,Department for Radiotherapy and Radiooncology, University Medical Center Giessen-Marburg, Marburg, Germany.,Marburg Iontherapy Center (MIT), Marburg, Germany
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20
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Baumann KS, Derksen L, Witt M, Michael Burg J, Engenhart-Cabillic R, Zink K. Monte Carlo calculation of beam quality correction factors in proton beams using FLUKA. Phys Med Biol 2021; 66. [PMID: 34378546 DOI: 10.1088/1361-6560/ac1c4b] [Citation(s) in RCA: 10] [Impact Index Per Article: 3.3] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/11/2021] [Accepted: 08/10/2021] [Indexed: 11/12/2022]
Abstract
Purpose.To provide Monte Carlo calculated beam quality correction factors (kQ) for monoenergetic proton beams using the Monte Carlo codefluka.Materials and methods.The Monte Carlo codeflukawas used to calculate the dose absorbed in a water-filled reference volume and the air-filled cavities of six plane-parallel and four cylindrical ionization chambers. The chambers were positioned at the entrance region of monoenergetic proton beams with energies between 60 and 250 MeV. Based on these dose values,fQas well askQfactors were calculated whilefQ0factors were taken from Andreoet al(2020Phys. Med. Biol.65095011).Results. kQfactors calculated in this work were found to agree with experimentally determinedkQfactors on the 1%-level, with only two exceptions with deviations of 1.4% and 1.9%. The comparison offQfactors calculated usingflukawithfQfactors calculated using the Monte Carlo codesgeant4 andpenhshowed a general good agreement for low energies, while differences for higher energies were pronounced. For high energies, in most cases the Monte Carlo codesflukaandgeant4 lead to comparable results while thefQfactors calculated withpenhare larger.Conclusion.flukacan be used to calculatekQfactors in clinical proton beams. The divergence of Monte Carlo calculatedkQfactors for high energies suggests that the role of nuclear interaction models implemented in the different Monte Carlo codes needs to be investigated in more detail.
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Affiliation(s)
- Kilian-Simon Baumann
- University Medical Center Giessen-Marburg, Department of Radiotherapy and Radiooncology, Marburg, Germany.,University of Applied Sciences, Institute of Medical Physics and Radiation Protection, Giessen, Germany.,Marburg Ion-Beam Therapy Center, Marburg, Germany
| | - Larissa Derksen
- University of Applied Sciences, Institute of Medical Physics and Radiation Protection, Giessen, Germany
| | - Matthias Witt
- University of Applied Sciences, Institute of Medical Physics and Radiation Protection, Giessen, Germany.,Marburg Ion-Beam Therapy Center, Marburg, Germany
| | - Jan Michael Burg
- University Medical Center Giessen-Marburg, Department of Radiotherapy and Radiooncology, Marburg, Germany.,University of Applied Sciences, Institute of Medical Physics and Radiation Protection, Giessen, Germany
| | - Rita Engenhart-Cabillic
- University Medical Center Giessen-Marburg, Department of Radiotherapy and Radiooncology, Marburg, Germany.,Marburg Ion-Beam Therapy Center, Marburg, Germany
| | - Klemens Zink
- University Medical Center Giessen-Marburg, Department of Radiotherapy and Radiooncology, Marburg, Germany.,University of Applied Sciences, Institute of Medical Physics and Radiation Protection, Giessen, Germany.,Marburg Ion-Beam Therapy Center, Marburg, Germany
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21
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Billas I, Bouchard H, Oelfke U, Duane S. Traceable reference dosimetry in MRI guided radiotherapy using alanine: calibration and magnetic field correction factors of ionisation chambers. Phys Med Biol 2021; 66. [PMID: 34049290 DOI: 10.1088/1361-6560/ac0680] [Citation(s) in RCA: 6] [Impact Index Per Article: 2.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/05/2020] [Accepted: 05/28/2021] [Indexed: 12/27/2022]
Abstract
Magnetic resonance imaging (MRI)-guided radiotherapy (RT) (MRIgRT) falls outside the scope of existing high energy photon therapy dosimetry protocols, because those protocols do not consider the effects of the magnetic field on detector response and on absorbed dose to water. The aim of this study is to evaluate and demonstrate the traceable measurement of absorbed dose in MRIgRT systems using alanine, made possible by the characterisation of alanine sensitivity to magnetic fields reported previously by Billaset al(2020Phys. Med. Biol.65115001), in a way which is compatible with existing standards and calibrations available for conventional RT. In this study, alanine is used to transfer absorbed dose to water to MRIgRT systems from a conventional linac. This offers an alternative route for the traceable measurement of absorbed dose to water, one which is independent of the transfer using ionisation chambers. The alanine dosimetry is analysed in combination with measurements with several Farmer-type chambers, PTW 30013 and IBA FC65-G, at six different centres and two different MRIgRT systems (Elekta Unity™ and ViewRay MRIdian™). The results are analysed in terms of the magnetic field correction factors, and in terms of the absorbed dose calibration coefficients for the chambers, determined at each centre. This approach to reference dosimetry in MRIgRT produces good consistency in the results, across the centres visited, at the level of 0.4% (standard deviation). Farmer-type ionisation chamber magnetic field correction factors were determined directly, by comparing calibrations in some MRIgRT systems with and without the magnetic field ramped up, and indirectly, by comparing calibrations in all the MRIgRT systems with calibrations in a conventional linac. Calibration coefficients in the MRIgRT systems were obtained with a standard uncertainty of 1.1% (Elekta Unity™) and 0.9% (ViewRay MRIdian™), for three different chamber orientations with respect to the magnetic field. The values obtained for the magnetic field correction factor in this investigation are consistent with those presented in the summary by de Pooteret al(2021Phys. Med. Biol.6605TR02), and would tend to support the adoption of a magnetic field correction factor which depends on the chamber type, PTW 30013 or IBA FC65-G.
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Affiliation(s)
- Ilias Billas
- National Physical Laboratory, Teddington, United Kingdom.,Joint Department of Physics, The Institute of Cancer Research and The Royal Marsden NHS Foundation Trust, London, United Kingdom
| | - Hugo Bouchard
- Université de Montréal, Département de Physique, Montréal, Canada and Centre Hospitalier de l'Université de Montréal, Montréal, Canada and Centre de recherche du CHUM, Montréal, Canada
| | - Uwe Oelfke
- Joint Department of Physics, The Institute of Cancer Research and The Royal Marsden NHS Foundation Trust, London, United Kingdom
| | - Simon Duane
- National Physical Laboratory, Teddington, United Kingdom
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Holm KM, Jäkel O, Krauss A. Water calorimetry-based kQfactors for Farmer-type ionization chambers in the SOBP of a carbon-ion beam. Phys Med Biol 2021; 66. [PMID: 34153952 DOI: 10.1088/1361-6560/ac0d0d] [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: 03/31/2021] [Accepted: 06/21/2021] [Indexed: 11/12/2022]
Abstract
The dosimetry of carbon-ion beams based on calibrated ionization chambers (ICs) still shows a significantly higher uncertainty compared to high-energy photon beams, a fact influenced mainly by the uncertainty of the correction factor for the beam qualitykQ. Due to a lack of experimental data,kQfactors in carbon-ion beams used today are based on theoretical calculations whose standard uncertainty is three times higher than that of photon beams. To reduce their uncertainty, in this work,kQfactors for two ICs were determined experimentally by means of water calorimetry for the spread-out Bragg peak of a carbon-ion beam, these factors are presented here for the first time. To this end, the absorbed dose to water in the12C-SOBP is measured using the water calorimeter developed at Physikalisch-Technische Bundesanstalt, allowing a direct calibration of the ICs used (PTW 30013 and IBA FC65G) and thereby an experimental determination of the chamber-specifickQfactors. Based on a detailed characterization of the irradiation field, correction factors for several effects that influence calorimetric and ionometric measurements were determined. Their contribution to an overall uncertainty budget of the finalkQfactors was determined, leading to a standard uncertainty forkQof 0.69%, which means a reduction by a factor of three compared to the theoretically calculated values. The experimentally determined values were expressed in accordance with TRS-398 and DIN 6801-1 and compared to the values given there. A maximum deviation of 2.3% was found between the experiment and the literature.
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Affiliation(s)
- Kim Marina Holm
- Department of Dosimetry for Radiation Therapy and Diagnostic Radiology, Physikalisch-Technische Bundesanstalt (PTB), Bundesallee 100, D-38116 Braunschweig, Germany.,Department of Medical Physics in Radiation Oncology, German Cancer Research Center (DKFZ), Im Neuenheimer Feld 280, D-69120 Heidelberg, Germany.,Heidelberg Institute for Radiation Oncology (HIRO), Heidelberg, Germany.,Department of Physics and Astronomy, University of Heidelberg, Im Neuenheimer Feld 226, D-69120 Heidelberg, Germany
| | - Oliver Jäkel
- Department of Medical Physics in Radiation Oncology, German Cancer Research Center (DKFZ), Im Neuenheimer Feld 280, D-69120 Heidelberg, Germany.,Heidelberg Institute for Radiation Oncology (HIRO), Heidelberg, Germany.,Heidelberg Ion Beam Therapy Center (HIT), University Hospital Heidelberg, Im Neuenheimer Feld 450, D-69120 Heidelberg, Germany
| | - Achim Krauss
- Department of Dosimetry for Radiation Therapy and Diagnostic Radiology, Physikalisch-Technische Bundesanstalt (PTB), Bundesallee 100, D-38116 Braunschweig, Germany
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Liu X, Li C, Zhu J, Gong G, Sun H, Li X, Sun M, Zhang Z, Li B, Yin Y, Li Z. Technical Note: End-to-end verification of an MR-Linac using a dynamic motion phantom. Med Phys 2021; 48:5479-5489. [PMID: 34174099 DOI: 10.1002/mp.15057] [Citation(s) in RCA: 6] [Impact Index Per Article: 2.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/28/2021] [Revised: 06/02/2021] [Accepted: 06/17/2021] [Indexed: 12/25/2022] Open
Abstract
PURPOSE MR-Linac integrates an MRI scanner and a linear accelerator to provide adaptive radiation treatment. Superior tissue contrast and real-time imaging can give the clinicians confidence to reduce the margins of the planning target volume (PTV). The purpose of this study was to verify the dosimetric accuracy of an MR-Linac system in treating a moving target and assess the error with different motion patterns and adaptation methods. METHODS We performed an end-to-end test for Elekta Unity (Elekta) using the 4D Dynamic Thorax Phantom (CIRS MRgRT 008Z), comparing the measured and planned dose. The moving phantom had four measurement locations in the tumor, liver, kidney, and spinal cord regions with a PTW30013 ion chamber. For seven different motion patterns, we first acquired simulation CT using a slow-scanning protocol, based on which we generated reference plans. The treatment technique was the standard intensity-modulated radiation therapy (IMRT). We tested both adaptation workflows: the Adapt-to-Position (ATP) and the Adapt-to-Shape (ATS). The three-dimensional (3D) distribution was measured using a diode array phantom (Sun Nuclear Inc.) to check the dose distribution accuracy as part of the routine QA process. We also performed end-to-end tests on a conventional Linac. Finally, we used SPSS Statistics 22.0 (Inc., Chicago, IL, USA) for data analysis. RESULTS All pretreatment reference plans and delivered plans had excellent QA results with a better than 95% passing rate of relative gamma analysis (2%/2 mm criteria). The adaptive planning for MR-Linac produced quality plans. The measured dose in the target agreed with the calculated dose. CONCLUSIONS The adaptive treatment on the MR-Linac system investigated met the expected performance with tumor motions. The outline of the target could be visualized and accurately contoured on the 3D MR for online planning. Under different motion patterns, the difference between the measured and calculated dose was acceptable clinically.
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Affiliation(s)
- Xuechun Liu
- Medical Engineering and Technology Research Center, Shandong First Medical University & Shandong Academy of Medical Sciences, Taian, China.,Department of Radiation Physics, Shandong Cancer Hospital and Institute, Shandong First Medical University and Shandong Academy of Medical Sciences, Jinan, China
| | - Chengqiang Li
- Department of Radiation Physics, Shandong Cancer Hospital and Institute, Shandong First Medical University and Shandong Academy of Medical Sciences, Jinan, China
| | - Jian Zhu
- Department of Radiation Physics, Shandong Cancer Hospital and Institute, Shandong First Medical University and Shandong Academy of Medical Sciences, Jinan, China
| | - Guanzhong Gong
- Department of Radiation Physics, Shandong Cancer Hospital and Institute, Shandong First Medical University and Shandong Academy of Medical Sciences, Jinan, China
| | | | - Xu Li
- Department of Radiation Physics, Shandong Cancer Hospital and Institute, Shandong First Medical University and Shandong Academy of Medical Sciences, Jinan, China
| | - Mengdi Sun
- Department of Radiation Physics, Shandong Cancer Hospital and Institute, Shandong First Medical University and Shandong Academy of Medical Sciences, Jinan, China
| | - Zicheng Zhang
- Department of Radiation Physics, Shandong Cancer Hospital and Institute, Shandong First Medical University and Shandong Academy of Medical Sciences, Jinan, China.,Department of Radiation Oncology, Shenzhen Traditional Chinese Medicine Hospital, The Fourth Clinical Medical of Guangzhou University of Chinese Medicine, Shenzhen, China
| | - Baosheng Li
- Department of Radiation Physics, Shandong Cancer Hospital and Institute, Shandong First Medical University and Shandong Academy of Medical Sciences, Jinan, China
| | - Yong Yin
- Department of Radiation Physics, Shandong Cancer Hospital and Institute, Shandong First Medical University and Shandong Academy of Medical Sciences, Jinan, China
| | - Zhenjiang Li
- Department of Radiation Physics, Shandong Cancer Hospital and Institute, Shandong First Medical University and Shandong Academy of Medical Sciences, Jinan, China
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Mirzakhanian L, Bassalow R, Zaks D, Huntzinger C, Seuntjens J. IAEA-AAPM TRS-483-based reference dosimetry of the new RefleXion biology-guided radiotherapy (BgRT) machine. Med Phys 2021; 48:1884-1892. [PMID: 33296515 DOI: 10.1002/mp.14631] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/26/2019] [Revised: 10/10/2020] [Accepted: 11/18/2020] [Indexed: 11/07/2022] Open
Abstract
PURPOSE The purpose of this study is to provide data for the calibration of the recent RefleXion TM biology-guided radiotherapy (BgRT) machine (Hayward, CA, USA) following the International Atomic Energy Agency (IAEA) and the American Association of Physicists in Medicine (AAPM) TRS-483 code of practice (COP) (Palmans et al. International Atomic Energy Agency, Vienna, 2017) and (Mirzakhanian et al. Med Phys, 2020). METHODS In RefleXion BgRT machine, reference dosimetry was performed using two methodologies described in TRS-483 and (Mirzakhanian et al. Med Phys, 2020) In the first approach (Approach 1), the generic beam quality correction factor k Q A , Q 0 f A , f ref was calculated using an accurate Monte Carlo (MC) model of the beam and of six ionization chamber types. The k Q A , Q 0 f A , f ref is a beam quality factor that corrects N D , w , Q 0 f ref (absorbed dose to water calibration coefficient in a calibration beam quality Q 0 ) for the differences between the response of the chamber in the conventional reference calibration field f ref with beam quality Q 0 at the standards laboratory and the response of the chamber in the user's A field f A with beam quality Q A . Field A represents the reference calibration field that does not fulfill msr conditions. In the second approach (Approach 2), a square equivalent field size was determined for field A of 10 × 2 cm 2 and 10 × 3 cm 2 . Knowing the equivalent field size, the beam quality specifier for the hypothetical 10 × 10 cm 2 field size was derived. This was used to calculate the beam quality correction factor analytically for the six chamber types using the TRS-398. (Andreo et al. Int Atom Energy Agency 420, 2001) Here, TRS-398 was used instead of TRS-483 since the beam quality correction values for the chambers used in this study are not tabulated in TRS-483. The accuracy of Approach 2 is studied in comparison to Approach 1. RESULTS Among the chambers, the PTW 31010 had the largest k Q A , Q 0 f A , f ref correction due to the volume averaging effect. The smallest-volume chamber (IBA CC01) had the smallest correction followed by the other microchambers Exradin-A14 and -A14SL. The equivalent square fields sizes were found to be 3.6 cm and 4.8 cm for the 10 × 2 cm 2 and 10 × 3 cm 2 field sizes, respectively. The beam quality correction factors calculated using the two approaches were within 0.27% for all chambers except IBA CC01. The latter chamber has an electrode made of steel and the differences between the correction calculated using the two approaches was the largest, that is, 0.5%. CONCLUSIONS In this study, we provided the k Q A , Q 0 f A , f ref values as a function of the beam quality specifier at the RefleXion BgRT setup ( TPR 20 , 10 ( S ) and % d d ( 10 , S ) x ) for six chamber types. We suggest using the first approach for calibration of the RefleXion BgRT machine. However, if the MC correction is not available for a user's detector, the user can use the second approach for estimating the beam quality correction factor to sufficient accuracy (0.3%) provided the chamber electrode is not made of high Z material.
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Affiliation(s)
| | - Rostem Bassalow
- RefleXion Medical, 25841 Industrial Blvd, Hayward, California, 94545, USA
| | - Daniel Zaks
- RefleXion Medical, 25841 Industrial Blvd, Hayward, California, 94545, USA
| | - Calvin Huntzinger
- RefleXion Medical, 25841 Industrial Blvd, Hayward, California, 94545, USA
| | - Jan Seuntjens
- Medical Physics Unit, McGill University, Montreal, Quebec, H4A 3J1, Canada
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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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26
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Pojtinger S, Nachbar M, Ghandour S, Pisaturo O, Pachoud M, Kapsch RP, Thorwarth D. Experimental determination of magnetic field correction factors for ionization chambers in parallel and perpendicular orientations. Phys Med Biol 2020; 65:245044. [PMID: 33181493 DOI: 10.1088/1361-6560/abca06] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/11/2022]
Abstract
Magnetic field correction factors are needed for absolute dosimetry in magnetic resonance (MR)-linacs. Currently experimental data for magnetic field correction factors, especially for small volume ionization chambers, are largely lacking. The purpose of this work is to establish, independent methods for the experimental determination of magnetic field correction factors [Formula: see text] in an orientation in which the ionization chamber is parallel to the magnetic field. The aim is to confirm previous experiments on the determination of Farmer type ionization chamber correction factors and to gather information about the usability of small-volume ionization chambers for absolute dosimetry in MR-linacs. The first approach to determine [Formula: see text] is based on a cross-calibration of measurements using a conventional linac with an electromagnet and an MR-linac. The absolute influence of the magnetic field in perpendicular orientation is quantified with the help of the conventional linac and the electromagnet. The correction factors for the parallel orientation are then derived by combining these measurements with relative measurements in the MR-linac. The second technique utilizes alanine electron paramagnetic resonance dosimetry. The alanine system as well as several ionization chambers were directly calibrated with the German primary standard for absorbed dose to water. Magnetic field correction factors for the ionization chambers were determined by a cross-calibration with the alanine in an MR-linac. Important quantities like [Formula: see text] for Farmer type ionization chambers in parallel orientation and the change of the dose to water due the magnetic field [Formula: see text] have been confirmed. In addition, magnetic field correction factors have been determined for small volume ionization chambers in parallel orientation. The electromagnet-based measurements of [Formula: see text] for [Formula: see text] MR-linacs and parallel ionization chamber orientations resulted in 0.9926(22), 0.9935(31) and 0.9841(27) for the PTW 30013, the PTW 31010 and the PTW 31021, respectively. The measurements based on the second technique resulted in values for [Formula: see text] of 0.9901(72), 0.9955(72), and 0.9885(71). Both methods show excellent accuracy and reproducibility and are therefore suitable for the determination of magnetic field correction factors. Small-volume ionization chambers showed a variation in the resulting values for [Formula: see text] and should be cross-calibrated instead of using tabulated values for correction factors.
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Affiliation(s)
- Stefan Pojtinger
- Physikalisch-Technische Bundesanstalt, Braunschweig, Germany. University Hospital Tübingen, Biomedical Physics, Tübingen, Germany
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27
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Czarnecki D, Zink K, Pimpinella M, Borbinha J, Teles P, Pinto M. Monte Carlo calculation of quality correction factors based on air kerma and absorbed dose to water in medium energy x-ray beams. Phys Med Biol 2020; 65:245042. [PMID: 33120372 DOI: 10.1088/1361-6560/abc5c9] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/12/2022]
Abstract
Clinical dosimetry is typically performed using ion chambers calibrated in terms of absorbed dose to water. As primary measurement standards for this quantity for low and medium energy x-rays are available only since a few years, most dosimetry protocols for this photon energy range are still based on air kerma calibration. For that reason, data for beam quality correction factors [Formula: see text], necessary for the application of dose to water based protocols, are scarce in literature. Currently the international IAEA TRS-398 Code of Practice is under revision and new [Formula: see text] factors for a large number of ion chambers will be introduced in the update of this protocol. Several international groups provided the IAEA with experimental and Monte Carlo based data for this revision. Within the European Community the EURAMET 16NRM03 RTNORM project was initiated for that purpose. In the present study, Monte Carlo based results for the beam quality correction factors in medium energy x-ray beams for six ion chambers applying different Monte Carlo codes are presented. Additionally, the perturbation factor p Q , necessary for the calculation of dose to water from an air kerma calibration coefficient, was determined. The beam quality correction factor [Formula: see text] for the chambers varied in the investigated energy range by about 4%-5%, and for five out of six chambers the data could be fitted by a simple logarithmic function, if the half-value-layer was used as the beam quality specifier. Corresponding data using different Monte Carlo codes for the same ion chamber agreed within 0.5%. For the perturbation factor p Q , the data did not obey a comparable simple relationship with the beam quality specifier. The variation of p Q for all ion chambers was in the range of 3%-4%. Compared to recently published data, our p Q data is around 1% larger, although the same Monte Carlo code has been used. Compared to the latest experimental data, there are even deviations in the range of 2%.
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Affiliation(s)
- Damian Czarnecki
- Institute of Medical Physics and Radiation Protection, University of Applied Sciences Giessen (THM), Giessen, Germany
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28
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Krauss A, Spindeldreier CK, Klüter S. Direct determination of [Formula: see text] for cylindrical ionization chambers in a 6 MV 0.35 T MR-linac. Phys Med Biol 2020; 65:235049. [PMID: 33300501 DOI: 10.1088/1361-6560/abab56] [Citation(s) in RCA: 7] [Impact Index Per Article: 1.8] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/11/2022]
Abstract
To ensure accurate reference dosimetry with ionization chambers in magnetic resonance linear accelerators (MR-linacs), the influence of the magnetic field on the response of the ionization chambers must be considered. The most direct method considering the influence of magnetic fields in dosimetry is to apply an appropriate absorbed-dose-to-water primary standard. At PTB, a new water calorimeter has been designed which is capable to determine Dw,Q in an MR-linac. The new device allows the direct calibration of ionization chambers in terms of absorbed dose to water for MR-linac irradiation conditions. Hence, the correction factors [Formula: see text] can be determined which replace the current radiation-quality dependent correction factors [Formula: see text] for dosimetry in the presence of magnetic fields. In cooperation with Heidelberg University Hospital,[Formula: see text] factors were measured at the 6 MV 0.35 T Viewray MR-linac for different cylindrical ionization chambers with sensitive volumes ranging from 0.015 cm3 to 0.65 cm3. The chambers were placed both perpendicular and parallel in respect to the magnetic field. Standard uncertainties of about 0.5% were achieved.
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Affiliation(s)
- A Krauss
- Department of Dosimetry for Radiation Therapy and Diagnostic Radiology, Physikalisch-Technische Bundesanstalt (PTB), Bundesallee 100, D-38116, Braunschweig, Germany
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Zink K. Twenty years after – das neue Dosimetrieprotokoll IAEA TRS-398 am Horizont sichtbar! Z Med Phys 2020; 30:249-251. [PMID: 33127206 DOI: 10.1016/j.zemedi.2020.09.007] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/26/2022]
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30
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Kretschmer J, Dulkys A, Brodbek L, Stelljes TS, Looe HK, Poppe B. Monte Carlo simulated beam quality and perturbation correction factors for ionization chambers in monoenergetic proton beams. Med Phys 2020; 47:5890-5905. [DOI: 10.1002/mp.14499] [Citation(s) in RCA: 7] [Impact Index Per Article: 1.8] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/26/2020] [Revised: 08/19/2020] [Accepted: 09/08/2020] [Indexed: 11/11/2022] Open
Affiliation(s)
- Jana Kretschmer
- University Clinic for Medical Radiation Physics Medical Campus Pius HospitalCarl‐von‐Ossietzky University Oldenburg Germany
| | - Anna Dulkys
- University Clinic for Medical Radiation Physics Medical Campus Pius HospitalCarl‐von‐Ossietzky University Oldenburg Germany
- Department of Radiation Therapy Helios Clinics Schwerin Schwerin Germany
| | - Leonie Brodbek
- University Clinic for Medical Radiation Physics Medical Campus Pius HospitalCarl‐von‐Ossietzky University Oldenburg Germany
- Department of Radiation Oncology University Medical Center GroningenUniversity of Groningen Groningen The Netherlands
| | - Tenzin Sonam Stelljes
- University Clinic for Medical Radiation Physics Medical Campus Pius HospitalCarl‐von‐Ossietzky University Oldenburg Germany
| | - Hui Khee Looe
- University Clinic for Medical Radiation Physics Medical Campus Pius HospitalCarl‐von‐Ossietzky University Oldenburg Germany
| | - Björn Poppe
- University Clinic for Medical Radiation Physics Medical Campus Pius HospitalCarl‐von‐Ossietzky University Oldenburg Germany
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