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Begg J, Jelen U, Keall P, Liney G, Holloway L. Experimental characterisation of the magnetic field correction factor,kB⃗,for Roos chambers in a parallel MRI-linac. Phys Med Biol 2022; 67. [PMID: 35413694 DOI: 10.1088/1361-6560/ac66b8] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/25/2021] [Accepted: 04/12/2022] [Indexed: 12/15/2022]
Abstract
Objective.Reference dosimetry on an MRI-linac requires a chamber specific magnetic field correction factor,kB⃗.This work aims to measure the correction factor for a parallel plate chamber on a parallel MRI-linac.Approach.kB⃗is defined as the ratio of the absorbed dose to water calibration coefficient in the presence of the magnetic field,ND,wB⃗relative to that under 0 T conditions,ND,w0T.kB⃗was measured via aND,wtransfer to a field chamber at each magnetic field strength from a chamber with knownND,wandkB⃗.This was achieved on the parallel MRI-linac by moving the measurement set-up between a high magnetic field strength region at the MRI-isocentre and a low magnetic field strength region at the end of the bore whilst maintaining consistent set-up and scatter conditions. Three PTW 34001 Roos chambers were investigated as well as a PTW 30013 Farmer used to validate methodology.Main Results.The beam quality used for the measurements ofkB⃗wasTPR20/10 = 0.632. ThekB⃗for the PTW Farmer chamber at 1 T on a parallel MRI-linac was 0.993 ± 0.013 (k = 1). The averagekB⃗factor measured for the three Roos chambers on a 1 T parallel MRI-linac was 0.999 ± 0.014 (k = 1).Significance.The results presented are the first measurements ofkB⃗for a Roos chamber on a parallel MRI-linac. The Roos chamber results demonstrate the potential for the chamber as a reference dosimeter in parallel MRI-linacs.
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Affiliation(s)
- Jarrad Begg
- Department of Medical Physics, Liverpool and Macarthur Cancer Therapy Centre, Liverpool, NSW, 2170, Australia.,Ingham Institute for Applied Medical Research, Liverpool, NSW, 2170, Australia.,South Western Sydney Clinical School, University of New South Wales, Liverpool, NSW, 2170, Australia
| | - Urszula Jelen
- Ingham Institute for Applied Medical Research, Liverpool, NSW, 2170, Australia
| | - Paul Keall
- Ingham Institute for Applied Medical Research, Liverpool, NSW, 2170, Australia.,Image X Institute, Faculty of Medicine and Health, University of Sydney, Camperdown, NSW, 2005, Australia
| | - Gary Liney
- Department of Medical Physics, Liverpool and Macarthur Cancer Therapy Centre, Liverpool, NSW, 2170, Australia.,Ingham Institute for Applied Medical Research, Liverpool, NSW, 2170, Australia.,South Western Sydney Clinical School, University of New South Wales, Liverpool, NSW, 2170, Australia.,Centre for Medical Radiation Physics, University of Wollongong, Wollongong, NSW, 2522, Australia
| | - Lois Holloway
- Department of Medical Physics, Liverpool and Macarthur Cancer Therapy Centre, Liverpool, NSW, 2170, Australia.,Ingham Institute for Applied Medical Research, Liverpool, NSW, 2170, Australia.,South Western Sydney Clinical School, University of New South Wales, Liverpool, NSW, 2170, Australia.,Centre for Medical Radiation Physics, University of Wollongong, Wollongong, NSW, 2522, Australia.,Institute of Medical Physics, University of Sydney, Camperdown, NSW, 2005, Australia
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2
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Lewis BC, Gu B, Klett R, Lotey R, Green OL, Kim T. Characterization of radiotherapy component impact on MR imaging quality for an MRgRT system. J Appl Clin Med Phys 2020; 21:20-26. [PMID: 33211375 PMCID: PMC7769410 DOI: 10.1002/acm2.13054] [Citation(s) in RCA: 3] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/01/2020] [Revised: 07/30/2020] [Accepted: 08/27/2020] [Indexed: 11/15/2022] Open
Abstract
Radiotherapy components of an magnetic resonnace-guided radiotherapy (MRgRT) system can alter the magnetic fields, causing spatial distortion and image deformation, altering imaging and radiation isocenter coincidence and the accuracy of dose calculations. This work presents a characterization of radiotherapy component impact on MR imaging quality in terms of imaging isocenter variation and spatial integrity changes on a 0.35T MRgRT system, pre- and postupgrade of the system. The impact of gantry position, MLC field size, and treatment table power state on imaging isocenter and spatial integrity were investigated. A spatial integrity phantom was used for all tests. Images were acquired for gantry angles 0-330° at 30° increments to assess the impact of gantry position. For MLC and table power state tests all images were acquired at the home gantry position (330°). MLC field sizes ranged from 1.66 to 27.4 cm edge length square fields. Imaging isocenter shift caused by gantry position was reduced from 1.7 mm at gantry 150° preupgrade to 0.9 mm at gantry 120° postupgrade. Maximum spatial integrity errors were 0.5 mm or less pre- and postupgrade for all gantry angles, MLC field sizes, and treatment table power states. However, when the treatment table was powered on, there was significant reduction in SNR. This study showed that gantry position can impact imaging isocenter, but spatial integrity errors were not dependent on gantry position, MLC field size, or treatment table power state. Significant isocenter variation, while reduced postupgrade, is cause for further investigation.
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Affiliation(s)
- Benjamin C. Lewis
- Department of Radiation OncologyWashington University School of MedicineSt LouisMOUSA
| | - Bruce Gu
- Department of Radiation OncologyWashington University School of MedicineSt LouisMOUSA
| | | | | | - Olga L. Green
- Department of Radiation OncologyWashington University School of MedicineSt LouisMOUSA
| | - Taeho Kim
- Department of Radiation OncologyWashington University School of MedicineSt LouisMOUSA
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3
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Alnaghy SJ, Causer T, Roberts N, Oborn B, Jelen U, Dong B, Gargett M, Begg J, Liney G, Petasecca M, Rosenfeld AB, Holloway L, Metcalfe P. High resolution silicon array detector implementation in an inline MRI-linac. Med Phys 2020; 47:1920-1929. [PMID: 31917865 DOI: 10.1002/mp.14016] [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: 04/17/2019] [Revised: 01/06/2020] [Accepted: 01/07/2020] [Indexed: 11/09/2022] Open
Abstract
PURPOSE Dynamic dosimaging is a concept whereby a detector in motion is tracked with magnetic resonance imaging (MRI) to validate the amount and position of dose in a radiation therapy treatment on an MRI-linac. This work takes steps toward the realization of dynamic dosimaging with the novel high resolution silicon array detector: MagicPlate-512 (M512). The performance of the M512 was assessed in a 1.0 T inline MRI-linac, without simultaneous imaging and then during an imaging sequence, both during dosimetry. MR images were acquired to determine the effect of the detector and its components on image quality. METHODS Beam profiles were measured using the M512 on the Australian MRI-Linac and a comparison made with Gafchromic EBT3 film to investigate any intrinsic magnetic field effects in the silicon. The M512 has 512 sensitive volumes, each 0.5 × 0.5 × 0.037 mm3 in dimension, organized in a two-dimensional array. Small field sizes up to 4.2 × 3.8 cm2 were investigated in both solid water and then solid lung phantoms. Beam profiles taken at 1.0 T were compared to 0 T conditions, and also to profiles taken during a gradient echo (GRE) imaging sequence. Differences in 80%-20% penumbral width and full width at half maximum (FWHM) were investigated. Localizer MR images were acquired of the detector adjacent to a water phantom. RESULTS Good agreement was observed between the M512 and film, with average differences in penumbral width and FWHM of <1 mm in the absence of the imaging sequence. Concurrent imaging widened the penumbra by up to 1.2 mm due to RF noise affecting the detector; film profiles were unchanged. Magnetic resonance images were affected by noise, in particular, due to the large amount of aluminum present, as well as from the USB cable, which acted as an antenna. Unfortunately, due to these issues, suitable dynamic dose imaging was not achieved with the current M512/phantom configuration and the MRI-linac. However, progress was made toward achieving this goal for future work. CONCLUSIONS The M512 silicon array detector successfully measured high-resolution beam profiles in agreement with Gafchromic film to within an average of <1 mm on the first MRI-linac in Australia. More effective noise reduction will be required for the achievement of dynamic dosimaging in the future.
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Affiliation(s)
- Sarah J Alnaghy
- Centre for Medical Radiation Physics, University of Wollongong, Wollongong, NSW, 2522, Australia.,Ingham Institute for Applied Medical Research, Liverpool, NSW, 2170, Australia
| | - Trent Causer
- Centre for Medical Radiation Physics, University of Wollongong, Wollongong, NSW, 2522, Australia.,Illawarra Cancer Care Centre, Wollongong Hospital, Wollongong, NSW, 2500, Australia
| | - Natalia Roberts
- Centre for Medical Radiation Physics, University of Wollongong, Wollongong, NSW, 2522, Australia.,Ingham Institute for Applied Medical Research, Liverpool, NSW, 2170, Australia
| | - Brad Oborn
- Centre for Medical Radiation Physics, University of Wollongong, Wollongong, NSW, 2522, Australia.,Illawarra Cancer Care Centre, Wollongong Hospital, Wollongong, NSW, 2500, Australia
| | - Urszula Jelen
- Ingham Institute for Applied Medical Research, Liverpool, NSW, 2170, Australia.,Department of Medical Physics, Liverpool and Macarthur Cancer Therapy Centre, Liverpool, NSW, 2170, Australia
| | - Bin Dong
- Ingham Institute for Applied Medical Research, Liverpool, NSW, 2170, Australia.,Department of Medical Physics, Liverpool and Macarthur Cancer Therapy Centre, Liverpool, NSW, 2170, Australia
| | - Maegan Gargett
- Centre for Medical Radiation Physics, University of Wollongong, Wollongong, NSW, 2522, Australia.,Northern Sydney Cancer Centre, Royal North Shore Hospital, St. Leonards, NSW, 2065, Australia
| | - Jarrad Begg
- Ingham Institute for Applied Medical Research, Liverpool, NSW, 2170, Australia.,Department of Medical Physics, Liverpool and Macarthur Cancer Therapy Centre, Liverpool, NSW, 2170, Australia.,South Western Sydney Clinical School, University of New South Wales, Liverpool, NSW, 2170, Australia
| | - Gary Liney
- Centre for Medical Radiation Physics, University of Wollongong, Wollongong, NSW, 2522, Australia.,Ingham Institute for Applied Medical Research, Liverpool, NSW, 2170, Australia.,Department of Medical Physics, Liverpool and Macarthur Cancer Therapy Centre, Liverpool, NSW, 2170, Australia.,South Western Sydney Clinical School, University of New South Wales, Liverpool, NSW, 2170, Australia
| | - Marco Petasecca
- Centre for Medical Radiation Physics, University of Wollongong, Wollongong, NSW, 2522, Australia
| | - Anatoly B Rosenfeld
- Centre for Medical Radiation Physics, University of Wollongong, Wollongong, NSW, 2522, Australia
| | - Lois Holloway
- Centre for Medical Radiation Physics, University of Wollongong, Wollongong, NSW, 2522, Australia.,Ingham Institute for Applied Medical Research, Liverpool, NSW, 2170, Australia.,Illawarra Cancer Care Centre, Wollongong Hospital, Wollongong, NSW, 2500, Australia.,Department of Medical Physics, Liverpool and Macarthur Cancer Therapy Centre, Liverpool, NSW, 2170, Australia.,South Western Sydney Clinical School, University of New South Wales, Liverpool, NSW, 2170, Australia.,Institute of Medical Physics, University of Sydney, Camperdown, NSW, 2505, Australia
| | - Peter Metcalfe
- Centre for Medical Radiation Physics, University of Wollongong, Wollongong, NSW, 2522, Australia.,Ingham Institute for Applied Medical Research, Liverpool, NSW, 2170, Australia
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4
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Lee D, Kim S, Palta J, Lewis B, Keall P, Kim T. A retrospective 4D-MRI based on 2D diaphragm profiles for lung cancer patients. J Med Imaging Radiat Oncol 2019; 63:360-369. [PMID: 30932353 DOI: 10.1111/1754-9485.12877] [Citation(s) in RCA: 8] [Impact Index Per Article: 1.6] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/12/2018] [Accepted: 02/22/2019] [Indexed: 11/30/2022]
Abstract
INTRODUCTION 4D-MRI, compared to 4D-CT, provides better soft-tissue contrast for target delineation. However, motion artefacts are often observed due to residual breathing variations. This study is to present a retrospective 4D-MRI reconstruction method based on 2D diaphragm profiles to improve the quality of 4D-MR images in the presence of significant breathing variations. METHODS The proposed 4D-MRI reconstruction method utilized diaphragm profiles (2D cine images on a single sagittal plan at the peak diaphragm) in conjunction with 4D-MR scans (2D-cine images on multiple pre-determined coronal planes along the anterior-posterior direction over a volume of interest). The diaphragm profile images were exploited to sort the 4D-MR scans by matching respiratory amplitude of diaphragm on the 4D-MR scans to the diaphragm profiles. To evaluate reconstructed 4D-MR images (ten 3D-MR images), sagittal images on ten 3D-MR images under free breathing (FB) and respiratory guidance (GB) were compared with diaphragm profile images (reference) from 13 healthy volunteers. RESULTS Forty-four 4D-MR scan datasets were successfully reconstructed without distinct respiratory-related motion artefacts even with the presence of breathing variation. The differences in diaphragm profiles between the reference and corresponding reconstructed images in the mean of root mean square were similar between FB (3.5 mm) and GB (3.0 mm), confirming that the 4D-MRI reconstruction method was effective even with significant breathing variation. CONCLUSIONS The diaphragm profiles were utilized to reconstruct 4D-MR images with spatial reliability and a fixed scan time under FB and GB. Our method can provide reliable 4D information of thoracic and abdominal regions for MRI-guided radiotherapy.
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Affiliation(s)
- Danny Lee
- School of Mathematical and Physical Science, University of Newcastle, Newcastle, New South Wales, Australia
| | - Siyong Kim
- Department of Radiation Oncology, Virginia Commonwealth University, Richmond, Virginia, USA
| | - Jatinder Palta
- Department of Radiation Oncology, Virginia Commonwealth University, Richmond, Virginia, USA
| | - Benjamin Lewis
- Department of Radiation Oncology, Virginia Commonwealth University, Richmond, Virginia, USA
| | - Paul Keall
- Radiation Physics Laboratory, Sydney Medical School, University of Sydney, Sydney, New South Wales, Australia
| | - Taeho Kim
- Radiation Oncology, School of Medicine, Washington University, St. Louis, Missouri, USA
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5
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Matsuoka T, Araki F, Ohno T. Perturbation effect of parallel-plate ionization chambers on buildup dose measurements in transverse magnetic fields. Phys Med 2019; 59:112-116. [DOI: 10.1016/j.ejmp.2019.03.011] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 12/10/2018] [Revised: 02/16/2019] [Accepted: 03/12/2019] [Indexed: 10/27/2022] Open
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6
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Wegener S, Weick S, Sauer OA. Influence of a transverse magnetic field on the response of different detectors in a high energy photon beam near the surface. Z Med Phys 2019; 29:22-30. [DOI: 10.1016/j.zemedi.2018.07.001] [Citation(s) in RCA: 4] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/22/2017] [Revised: 05/29/2018] [Accepted: 07/02/2018] [Indexed: 10/28/2022]
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7
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Liney G, Whelan B, Oborn B, Barton M, Keall P. MRI-Linear Accelerator Radiotherapy Systems. Clin Oncol (R Coll Radiol) 2018; 30:686-691. [DOI: 10.1016/j.clon.2018.08.003] [Citation(s) in RCA: 54] [Impact Index Per Article: 9.0] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/13/2018] [Revised: 07/25/2018] [Accepted: 08/20/2018] [Indexed: 12/25/2022]
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8
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Wachowicz K, Murray B, Fallone BG. On the direct acquisition of beam's-eye-view images in MRI for integration with external beam radiotherapy. Phys Med Biol 2018; 63:125002. [PMID: 29771238 DOI: 10.1088/1361-6560/aac5b9] [Citation(s) in RCA: 4] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/12/2022]
Abstract
The recent interest in the integration of external beam radiotherapy with a magnetic resonance (MR) imaging unit offers the potential for real-time adaptive tumour tracking during radiation treatment. The tracking of large tumours which follow a rapid trajectory may best be served by the generation of a projection image from the perspective of the beam source, or 'beam's eye view' (BEV). This type of image projection represents the path of the radiation beam, thus enabling rapid compensations for target translations, rotations and deformations, as well time-dependent critical structure avoidance. MR units have been traditionally incapable of this type of imaging except through lengthy 3D acquisitions and ray tracing procedures. This work investigates some changes to the traditional MR scanner architecture that would permit the direct acquisition of a BEV image suitable for integration with external beam radiotherapy. Based on the theory presented in this work, a phantom was imaged with nonlinear encoding-gradient field patterns to demonstrate the technique. The phantom was constructed with agarose gel tubes spaced two cm apart at their base and oriented to converge towards an imaginary beam source 100 cm away. A corresponding virtual phantom was also created and subjected to the same encoding technique as in the physical demonstration, allowing the method to be tested without hardware limitations. The experimentally acquired and simulated images indicate the feasibility of the technique, showing a substantial amount of blur reduction in a diverging phantom compared to the conventional imaging geometry, particularly with the nonlinear gradients ideally implemented. The theory is developed to demonstrate that the method can be adapted in a number of different configurations to accommodate all proposed integration schemes for MR units and radiotherapy sources. Depending on the configuration, the implementation of this technique will require between two and four additional nonlinear encoding coils.
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Affiliation(s)
- K Wachowicz
- Department of Medical Physics, Cross Cancer Institute, 11560 University Avenue, Edmonton, Alberta T6G 1Z2, Canada. Department of Oncology, University of Alberta, 11560 University Avenue, Edmonton, Alberta T6G 1Z2, Canada
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9
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Whelan B, Kolling S, Oborn BM, Keall P. Passive magnetic shielding in MRI-Linac systems. Phys Med Biol 2018; 63:075008. [PMID: 29578113 DOI: 10.1088/1361-6560/aab138] [Citation(s) in RCA: 10] [Impact Index Per Article: 1.7] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/12/2022]
Abstract
Passive magnetic shielding refers to the use of ferromagnetic materials to redirect magnetic field lines away from vulnerable regions. An application of particular interest to the medical physics community is shielding in MRI systems, especially integrated MRI-linear accelerator (MRI-Linac) systems. In these systems, the goal is not only to minimize the magnetic field in some volume, but also to minimize the impact of the shield on the magnetic fields within the imaging volume of the MRI scanner. In this work, finite element modelling was used to assess the shielding of a side coupled 6 MV linac and resultant heterogeneity induced within the 30 cm diameter of spherical volume (DSV) of a novel 1 Tesla split bore MRI magnet. A number of different shield parameters were investigated; distance between shield and magnet, shield shape, shield thickness, shield length, openings in the shield, number of concentric layers, spacing between each layer, and shield material. Both the in-line and perpendicular MRI-Linac configurations were studied. By modifying the shield shape around the linac from the starting design of an open ended cylinder, the shielding effect was boosted by approximately 70% whilst the impact on the magnet was simultaneously reduced by approximately 10%. Openings in the shield for the RF port and beam exit were substantial sources of field leakage; however it was demonstrated that shielding could be added around these openings to compensate for this leakage. Layering multiple concentric shield shells was highly effective in the perpendicular configuration, but less so for the in-line configuration. Cautious use of high permeability materials such as Mu-metal can greatly increase the shielding performance in some scenarios. In the perpendicular configuration, magnetic shielding was more effective and the impact on the magnet lower compared with the in-line configuration.
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Affiliation(s)
- Brendan Whelan
- Radiation Physics Laboratory, University of Sydney, Sydney (NSW), 2006, Australia. Ingham Institute for Applied Medical Research, Liverpool (NSW), 2170, Australia. Author to whom any correspondence should be addressed
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10
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Alnaghy SJ, Begg J, Causer T, Alharthi T, Glaubes L, Dong B, George A, Holloway L, Metcalfe P. Technical Note: Penumbral width trimming in solid lung dose profiles for 0.9 and 1.5 T MRI-Linac prototypes. Med Phys 2017; 45:479-487. [DOI: 10.1002/mp.12680] [Citation(s) in RCA: 6] [Impact Index Per Article: 0.9] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/05/2017] [Revised: 09/19/2017] [Accepted: 11/07/2017] [Indexed: 11/10/2022] Open
Affiliation(s)
- Sarah J. Alnaghy
- Centre for Medical Radiation Physics; University of Wollongong; Wollongong NSW 2522 Australia
- Ingham Institute for Applied Medical Research; Liverpool NSW 2170 Australia
| | - Jarrad Begg
- Ingham Institute for Applied Medical Research; Liverpool NSW 2170 Australia
- Department of Medical Physics; Liverpool and Macarthur Cancer Therapy Centre; Liverpool NSW 2170 Australia
- South Western Sydney Clinical School; University of New South Wales, Liverpool; NSW 2170 Australia
| | - Trent Causer
- Centre for Medical Radiation Physics; University of Wollongong; Wollongong NSW 2522 Australia
- Ingham Institute for Applied Medical Research; Liverpool NSW 2170 Australia
- Illawarra Cancer Care Centre; Wollongong Hospital; Wollongong NSW 2500 Australia
| | - Thahabah Alharthi
- Ingham Institute for Applied Medical Research; Liverpool NSW 2170 Australia
- Institute of Medical Physics; University of Sydney; Camperdown NSW 2505 Australia
| | - Laura Glaubes
- Institute of Medical Physics; University of Sydney; Camperdown NSW 2505 Australia
| | - Bin Dong
- Centre for Medical Radiation Physics; University of Wollongong; Wollongong NSW 2522 Australia
- Ingham Institute for Applied Medical Research; Liverpool NSW 2170 Australia
- Department of Medical Physics; Liverpool and Macarthur Cancer Therapy Centre; Liverpool NSW 2170 Australia
| | - Armia George
- Ingham Institute for Applied Medical Research; Liverpool NSW 2170 Australia
- Department of Medical Physics; Liverpool and Macarthur Cancer Therapy Centre; Liverpool NSW 2170 Australia
| | - Lois Holloway
- Centre for Medical Radiation Physics; University of Wollongong; Wollongong NSW 2522 Australia
- Ingham Institute for Applied Medical Research; Liverpool NSW 2170 Australia
- Department of Medical Physics; Liverpool and Macarthur Cancer Therapy Centre; Liverpool NSW 2170 Australia
- South Western Sydney Clinical School; University of New South Wales, Liverpool; NSW 2170 Australia
- Institute of Medical Physics; University of Sydney; Camperdown NSW 2505 Australia. Sydney Medical School; University of Sydney; Camperdown NSW 2505 Australia
| | - Peter Metcalfe
- Centre for Medical Radiation Physics; University of Wollongong; Wollongong NSW 2522 Australia
- Ingham Institute for Applied Medical Research; Liverpool NSW 2170 Australia
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11
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Papalazarou C, Klop GJ, Milder MT, Marijnissen JP, Gupta V, Heijmen BJ, Nuyttens JJ, Hoogeman MS. CyberKnife with integrated CT-on-rails: System description and first clinical application for pancreas SBRT. Med Phys 2017; 44:4816-4827. [DOI: 10.1002/mp.12432] [Citation(s) in RCA: 22] [Impact Index Per Article: 3.1] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/26/2017] [Revised: 06/05/2017] [Accepted: 06/15/2017] [Indexed: 12/16/2022] Open
Affiliation(s)
- Chrysi Papalazarou
- Department of Radiation Oncology; Erasmus MC Cancer Institute; Groene Hilledijk 301 Rotterdam 3075 EA The Netherlands
| | - Gijsbert J. Klop
- Department of Radiation Oncology; Erasmus MC Cancer Institute; Groene Hilledijk 301 Rotterdam 3075 EA The Netherlands
| | - Maaike T.W. Milder
- Department of Radiation Oncology; Erasmus MC Cancer Institute; Groene Hilledijk 301 Rotterdam 3075 EA The Netherlands
| | - Johannes P.A. Marijnissen
- Department of Radiation Oncology; Erasmus MC Cancer Institute; Groene Hilledijk 301 Rotterdam 3075 EA The Netherlands
| | - Vikas Gupta
- Department of Radiation Oncology; Erasmus MC Cancer Institute; Groene Hilledijk 301 Rotterdam 3075 EA The Netherlands
| | - Ben J.M. Heijmen
- Department of Radiation Oncology; Erasmus MC Cancer Institute; Groene Hilledijk 301 Rotterdam 3075 EA The Netherlands
| | - Joost J.M.E. Nuyttens
- Department of Radiation Oncology; Erasmus MC Cancer Institute; Groene Hilledijk 301 Rotterdam 3075 EA The Netherlands
| | - Mischa S. Hoogeman
- Department of Radiation Oncology; Erasmus MC Cancer Institute; Groene Hilledijk 301 Rotterdam 3075 EA The Netherlands
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12
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Arivarasan I, Anuradha C, Subramanian S, Anantharaman A, Ramasubramanian V. Magnetic resonance image guidance in external beam radiation therapy planning and delivery. Jpn J Radiol 2017; 35:417-426. [DOI: 10.1007/s11604-017-0656-5] [Citation(s) in RCA: 10] [Impact Index Per Article: 1.4] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/28/2017] [Accepted: 05/29/2017] [Indexed: 12/14/2022]
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13
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Jia X, Tian Z, Xi Y, Jiang SB, Wang G. New concept on an integrated interior magnetic resonance imaging and medical linear accelerator system for radiation therapy. J Med Imaging (Bellingham) 2017; 4:015004. [PMID: 28331888 DOI: 10.1117/1.jmi.4.1.015004] [Citation(s) in RCA: 5] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/08/2016] [Accepted: 02/13/2017] [Indexed: 12/25/2022] Open
Abstract
Image guidance plays a critical role in radiotherapy. Currently, cone-beam computed tomography (CBCT) is routinely used in clinics for this purpose. While this modality can provide an attenuation image for therapeutic planning, low soft-tissue contrast affects the delineation of anatomical and pathological features. Efforts have recently been devoted to several MRI linear accelerator (LINAC) projects that lead to the successful combination of a full diagnostic MRI scanner with a radiotherapy machine. We present a new concept for the development of the MRI-LINAC system. Instead of combining a full MRI scanner with the LINAC platform, we propose using an interior MRI (iMRI) approach to image a specific region of interest (RoI) containing the radiation treatment target. While the conventional CBCT component still delivers a global image of the patient's anatomy, the iMRI offers local imaging of high soft-tissue contrast for tumor delineation. We describe a top-level system design for the integration of an iMRI component into an existing LINAC platform. We performed numerical analyses of the magnetic field for the iMRI to show potentially acceptable field properties in a spherical RoI with a diameter of 15 cm. This field could be shielded to a sufficiently low level around the LINAC region to avoid electromagnetic interference. Furthermore, we investigate the dosimetric impacts of this integration on the radiotherapy beam.
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Affiliation(s)
- Xun Jia
- University of Texas Southwestern Medical Center , Department of Radiation Oncology, Dallas, Texas, United States
| | - Zhen Tian
- University of Texas Southwestern Medical Center , Department of Radiation Oncology, Dallas, Texas, United States
| | - Yan Xi
- Biomedical Imaging Center , Rensselaer Polytechnic Institute, Troy, New York, United States
| | - Steve B Jiang
- University of Texas Southwestern Medical Center , Department of Radiation Oncology, Dallas, Texas, United States
| | - Ge Wang
- Biomedical Imaging Center , Rensselaer Polytechnic Institute, Troy, New York, United States
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14
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Fuchs H, Moser P, Gröschl M, Georg D. Magnetic field effects on particle beams and their implications for dose calculation in MR-guided particle therapy. Med Phys 2017; 44:1149-1156. [DOI: 10.1002/mp.12105] [Citation(s) in RCA: 42] [Impact Index Per Article: 6.0] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/19/2016] [Revised: 01/05/2017] [Accepted: 01/06/2017] [Indexed: 11/05/2022] Open
Affiliation(s)
- Hermann Fuchs
- Department of Radiation Oncology; Medical University of Vienna/AKH; Vienna Austria
- Christian Doppler Laboratory for Medical Radiation Research for Radiation Oncology; Medical University of Vienna; Vienna Austria
| | - Philipp Moser
- Department of Radiation Oncology; Medical University of Vienna/AKH; Vienna Austria
- Christian Doppler Laboratory for Medical Radiation Research for Radiation Oncology; Medical University of Vienna; Vienna Austria
- Institute of Applied Physics; Vienna University of Technology; Vienna Austria
| | - Martin Gröschl
- Institute of Applied Physics; Vienna University of Technology; Vienna Austria
| | - Dietmar Georg
- Department of Radiation Oncology; Medical University of Vienna/AKH; Vienna Austria
- Christian Doppler Laboratory for Medical Radiation Research for Radiation Oncology; Medical University of Vienna; Vienna Austria
- Comprehensive Cancer Center; Medical University of Vienna/AKH; Vienna Austria
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15
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Lee D, Greer PB, Pollock S, Kim T, Keall P. Quantifying the accuracy of the tumor motion and area as a function of acceleration factor for the simulation of the dynamic keyhole magnetic resonance imaging method. Med Phys 2017; 43:2639. [PMID: 27147373 DOI: 10.1118/1.4947508] [Citation(s) in RCA: 6] [Impact Index Per Article: 0.9] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/25/2022] Open
Abstract
PURPOSE The dynamic keyhole is a new MR image reconstruction method for thoracic and abdominal MR imaging. To date, this method has not been investigated with cancer patient magnetic resonance imaging (MRI) data. The goal of this study was to assess the dynamic keyhole method for the task of lung tumor localization using cine-MR images reconstructed in the presence of respiratory motion. METHODS The dynamic keyhole method utilizes a previously acquired a library of peripheral k-space datasets at similar displacement and phase (where phase is simply used to determine whether the breathing is inhale to exhale or exhale to inhale) respiratory bins in conjunction with central k-space datasets (keyhole) acquired. External respiratory signals drive the process of sorting, matching, and combining the two k-space streams for each respiratory bin, thereby achieving faster image acquisition without substantial motion artifacts. This study was the first that investigates the impact of k-space undersampling on lung tumor motion and area assessment across clinically available techniques (zero-filling and conventional keyhole). In this study, the dynamic keyhole, conventional keyhole and zero-filling methods were compared to full k-space dataset acquisition by quantifying (1) the keyhole size required for central k-space datasets for constant image quality across sixty four cine-MRI datasets from nine lung cancer patients, (2) the intensity difference between the original and reconstructed images in a constant keyhole size, and (3) the accuracy of tumor motion and area directly measured by tumor autocontouring. RESULTS For constant image quality, the dynamic keyhole method, conventional keyhole, and zero-filling methods required 22%, 34%, and 49% of the keyhole size (P < 0.0001), respectively, compared to the full k-space image acquisition method. Compared to the conventional keyhole and zero-filling reconstructed images with the keyhole size utilized in the dynamic keyhole method, an average intensity difference of the dynamic keyhole reconstructed images (P < 0.0001) was minimal, and resulted in the accuracy of tumor motion within 99.6% (P < 0.0001) and the accuracy of tumor area within 98.0% (P < 0.0001) for lung tumor monitoring applications. CONCLUSIONS This study demonstrates that the dynamic keyhole method is a promising technique for clinical applications such as image-guided radiation therapy requiring the MR monitoring of thoracic tumors. Based on the results from this study, the dynamic keyhole method could increase the imaging frequency by up to a factor of five compared with full k-space methods for real-time lung tumor MRI.
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Affiliation(s)
- Danny Lee
- Radiation Physics Laboratory, Sydney Medical School, University of Sydney, Sydney, NSW 2006, Australia
| | - Peter B Greer
- School of Mathematical and Physical Sciences, University of Newcastle, Newcastle, NSW 2308, Australia and Department of Radiation Oncology, Calvary Mater Newcastle Hospital, Newcastle, NSW 2298, Australia
| | - Sean Pollock
- Radiation Physics Laboratory, Sydney Medical School, University of Sydney, Sydney, NSW 2006, Australia
| | - Taeho Kim
- Radiation Physics Laboratory, Sydney Medical School, University of Sydney, Sydney, NSW 2006, Australia and Department of Radiation Oncology, Virginia Commonwealth University, Richmond, Virginia 23219
| | - Paul Keall
- Radiation Physics Laboratory, Sydney Medical School, University of Sydney, Sydney, NSW 2006, Australia
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Whelan B, Gierman S, Holloway L, Schmerge J, Keall P, Fahrig R. A novel electron accelerator for MRI-Linac radiotherapy. Med Phys 2016; 43:1285-94. [PMID: 26936713 DOI: 10.1118/1.4941309] [Citation(s) in RCA: 13] [Impact Index Per Article: 1.6] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/07/2022] Open
Abstract
PURPOSE MRI guided radiotherapy is a rapidly growing field; however, current electron accelerators are not designed to operate in the magnetic fringe fields of MRI scanners. As such, current MRI-Linac systems require magnetic shielding, which can degrade MR image quality and limit system flexibility. The purpose of this work was to develop and test a novel medical electron accelerator concept which is inherently robust to operation within magnetic fields for in-line MRI-Linac systems. METHODS Computational simulations were utilized to model the accelerator, including the thermionic emission process, the electromagnetic fields within the accelerating structure, and resulting particle trajectories through these fields. The spatial and energy characteristics of the electron beam were quantified at the accelerator target and compared to published data for conventional accelerators. The model was then coupled to the fields from a simulated 1 T superconducting magnet and solved for cathode to isocenter distances between 1.0 and 2.4 m; the impact on the electron beam was quantified. RESULTS For the zero field solution, the average current at the target was 146.3 mA, with a median energy of 5.8 MeV (interquartile spread of 0.1 MeV), and a spot size diameter of 1.5 mm full-width-tenth-maximum. Such an electron beam is suitable for therapy, comparing favorably to published data for conventional systems. The simulated accelerator showed increased robustness to operation in in-line magnetic fields, with a maximum current loss of 3% compared to 85% for a conventional system in the same magnetic fields. CONCLUSIONS Computational simulations suggest that replacing conventional DC electron sources with a RF based source could be used to develop medical electron accelerators which are robust to operation in in-line magnetic fields. This would enable the development of MRI-Linac systems with no magnetic shielding around the Linac and reduce the requirements for optimization of magnetic fringe field, simplify design of the high-field magnet, and increase system flexibility.
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Affiliation(s)
- Brendan Whelan
- Radiation Physics Laboratory, University of Sydney, Sydney, NSW 2006, Australia and Liverpool and Macarthur Cancer Therapy Centres and Ingham Institute for Applied Medical Research, Liverpool, NSW 2170, Australia
| | | | - Lois Holloway
- Liverpool and Macarthur Cancer Therapy Centres and Ingham Institute for Applied Medical Research, Liverpool, NSW 2170, Australia
| | - John Schmerge
- SLAC National Laboratory, Menlo Park, California 94025
| | - Paul Keall
- Radiation Physics Laboratory, University of Sydney, Sydney, NSW 2006, Australia and Liverpool and Macarthur Cancer Therapy Centres and Ingham Institute for Applied Medical Research, Liverpool, NSW 2170, Australia
| | - Rebecca Fahrig
- Department of Radiology, Stanford University, Palo Alto, California 94305
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Lee D, Greer PB, Ludbrook J, Arm J, Hunter P, Pollock S, Makhija K, O'brien RT, Kim T, Keall P. Audiovisual Biofeedback Improves Cine-Magnetic Resonance Imaging Measured Lung Tumor Motion Consistency. Int J Radiat Oncol Biol Phys 2015; 94:628-36. [PMID: 26867892 DOI: 10.1016/j.ijrobp.2015.11.017] [Citation(s) in RCA: 24] [Impact Index Per Article: 2.7] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/16/2015] [Revised: 08/01/2015] [Accepted: 11/11/2015] [Indexed: 12/25/2022]
Abstract
PURPOSE To assess the impact of an audiovisual (AV) biofeedback on intra- and interfraction tumor motion for lung cancer patients. METHODS AND MATERIALS Lung tumor motion was investigated in 9 lung cancer patients who underwent a breathing training session with AV biofeedback before 2 3T magnetic resonance imaging (MRI) sessions. The breathing training session was performed to allow patients to become familiar with AV biofeedback, which uses a guiding wave customized for each patient according to a reference breathing pattern. In the first MRI session (pretreatment), 2-dimensional cine-MR images with (1) free breathing (FB) and (2) AV biofeedback were obtained, and the second MRI session was repeated within 3-6 weeks (mid-treatment). Lung tumors were directly measured from cine-MR images using an auto-segmentation technique; the centroid and outlier motions of the lung tumors were measured from the segmented tumors. Free breathing and AV biofeedback were compared using several metrics: intra- and interfraction tumor motion consistency in displacement and period, and the outlier motion ratio. RESULTS Compared with FB, AV biofeedback improved intrafraction tumor motion consistency by 34% in displacement (P=.019) and by 73% in period (P<.001). Compared with FB, AV biofeedback improved interfraction tumor motion consistency by 42% in displacement (P<.046) and by 74% in period (P=.005). Compared with FB, AV biofeedback reduced the outlier motion ratio by 21% (P<.001). CONCLUSIONS These results demonstrated that AV biofeedback significantly improved intra- and interfraction lung tumor motion consistency for lung cancer patients. These results demonstrate that AV biofeedback can facilitate consistent tumor motion, which is advantageous toward achieving more accurate medical imaging and radiation therapy procedures.
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Affiliation(s)
- Danny Lee
- Radiation Physics Laboratory, Sydney Medical School, The University of Sydney, Sidney, NSW, Australia
| | - Peter B Greer
- School of Mathematical and Physical Sciences, The University of Newcastle, Newcastle, NSW, Australia; Department of Radiation Oncology, Calvary Mater Newcastle, Newcastle, NSW, Australia
| | - Joanna Ludbrook
- Department of Radiation Oncology, Calvary Mater Newcastle, Newcastle, NSW, Australia
| | - Jameen Arm
- Department of Radiation Oncology, Calvary Mater Newcastle, Newcastle, NSW, Australia
| | - Perry Hunter
- Department of Radiation Oncology, Calvary Mater Newcastle, Newcastle, NSW, Australia
| | - Sean Pollock
- Radiation Physics Laboratory, Sydney Medical School, The University of Sydney, Sidney, NSW, Australia
| | - Kuldeep Makhija
- Radiation Physics Laboratory, Sydney Medical School, The University of Sydney, Sidney, NSW, Australia
| | - Ricky T O'brien
- Radiation Physics Laboratory, Sydney Medical School, The University of Sydney, Sidney, NSW, Australia
| | - Taeho Kim
- Radiation Physics Laboratory, Sydney Medical School, The University of Sydney, Sidney, NSW, Australia; Department of Radiation Oncology, Virginia Commonwealth University, Richmond, Virginia
| | - Paul Keall
- Radiation Physics Laboratory, Sydney Medical School, The University of Sydney, Sidney, NSW, Australia.
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Oborn BM, Dowdell S, Metcalfe PE, Crozier S, Mohan R, Keall PJ. Proton beam deflection in MRI fields: Implications for MRI-guided proton therapy. Med Phys 2015; 42:2113-24. [DOI: 10.1118/1.4916661] [Citation(s) in RCA: 54] [Impact Index Per Article: 6.0] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/07/2022] Open
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Keall PJ, Barton M, Crozier S. The Australian Magnetic Resonance Imaging–Linac Program. Semin Radiat Oncol 2014; 24:203-6. [DOI: 10.1016/j.semradonc.2014.02.015] [Citation(s) in RCA: 255] [Impact Index Per Article: 25.5] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/28/2022]
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Lee D, Pollock S, Whelan B, Keall P, Kim T. Dynamic keyhole: A novel method to improve MR images in the presence of respiratory motion for real-time MRI. Med Phys 2014; 41:072304. [DOI: 10.1118/1.4883882] [Citation(s) in RCA: 9] [Impact Index Per Article: 0.9] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/25/2022] Open
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21
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Kolling S, Oborn BM, Keall PJ, Horvat J. Magnetization curves of sintered heavy tungsten alloys for applications in MRI-guided radiotherapy. Med Phys 2014; 41:061707. [PMID: 24877802 DOI: 10.1118/1.4873679] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/07/2022] Open
Abstract
PURPOSE Due to the current interest in MRI-guided radiotherapy, the magnetic properties of the materials commonly used in radiotherapy are becoming increasingly important. In this paper, measurement results for the magnetization (BH) curves of a range of sintered heavy tungsten alloys used in radiation shielding and collimation are presented. METHODS Sintered heavy tungsten alloys typically contain >90% tungsten and <10% of a combination of iron, nickel, and copper binders. Samples of eight different grades of sintered heavy tungsten alloys with varying binder content were investigated. Using a superconducting quantum interference detector magnetometer, the induced magnetic moment m was measured for each sample as a function of applied external field H0 and the BH curve derived. RESULTS The iron content of the alloys was found to play a dominant role, directly influencing the magnetization M and thus the nonlinearity of the BH curve. Generally, the saturation magnetization increased with increasing iron content of the alloy. Furthermore, no measurable magnetization was found for all alloys without iron content, despite containing up to 6% of nickel. For two samples from different manufacturers but with identical quoted nominal elemental composition (95% W, 3.5% Ni, 1.5% Fe), a relative difference in the magnetization of 11%-16% was measured. CONCLUSIONS The measured curves show that the magnetic properties of sintered heavy tungsten alloys strongly depend on the iron content, whereas the addition of nickel in the absence of iron led to no measurable effect. Since a difference in the BH curves for two samples with identical quoted nominal composition from different manufacturers was observed, measuring of the BH curve for each individual batch of heavy tungsten alloys is advisable whenever accurate knowledge of the magnetic properties is crucial. The obtained BH curves can be used in FEM simulations to predict the magnetic impact of sintered heavy tungsten alloys.
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Affiliation(s)
- Stefan Kolling
- Sydney Medical School, University of Sydney, NSW 2006, Australia
| | - Bradley M Oborn
- Illawarra Cancer Care Centre (ICCC), Wollongong, NSW 2500, Australia and Centre for Medical Radiation Physics (CMRP), University of Wollongong, Wollongong, NSW 2500, Australia
| | - Paul J Keall
- Sydney Medical School, University of Sydney, NSW 2006, Australia and Ingham Institute for Applied Medical Research, Liverpool, NSW 2170, Australia
| | - Joseph Horvat
- Institute for Superconducting and Electronic Materials, University of Wollongong, Wollongong, NSW 2500, Australia and School of Physics, University of Wollongong, Wollongong, NSW 2500, Australia
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Oborn BM, Kolling S, Metcalfe PE, Crozier S, Litzenberg DW, Keall PJ. Electron contamination modeling and reduction in a 1 T open bore inline MRI-linac system. Med Phys 2014; 41:051708. [DOI: 10.1118/1.4871618] [Citation(s) in RCA: 38] [Impact Index Per Article: 3.8] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/07/2022] Open
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