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Sritharan K, Daamen L, Pathmanathan A, Schytte T, Pos F, Choudhury A, van der Voort van Zyp JR, Kerkmeijer LG, Hall W, Hall E, Verkooijen HM, Herbert T, Hafeez S, Mitchell A, Tree AC. MRI-guided radiotherapy in twenty fractions for localised prostate cancer; results from the MOMENTUM study. Clin Transl Radiat Oncol 2024; 46:100742. [PMID: 38440792 PMCID: PMC10909700 DOI: 10.1016/j.ctro.2024.100742] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/29/2023] [Revised: 01/30/2024] [Accepted: 02/03/2024] [Indexed: 03/06/2024] Open
Abstract
Background and purpose MRI-guided radiotherapy (MRIgRT) offers multiple potential advantages over CT-guidance. This study examines the potential clinical benefits of MRIgRT for men with localised prostate cancer, in the setting of moderately hypofractionated radiotherapy. We evaluate two-year toxicity outcomes, early biochemical response and patient-reported outcomes (PRO), using data obtained from a multicentre international registry study, for the first group of patients with prostate cancer who underwent treatment on a 1.5 T MR-Linac. Materials and methods Patients who were enrolled within the MOMENTUM study and received radical treatment with 60 Gy in 20 fractions were identified. PSA levels and CTCAE version 5.0 toxicity data were measured at follow-up visits. Those patients who consented to PRO data collection also completed EQ-5D-5L, EORTC QLQ-C30 and EORTC QLQ-PR25 questionnaires. Results Between November 2018 and June 2022, 146 patients who had MRIgRT for localised prostate cancer on the 1.5 T MR-Linac were eligible for this study. Grade 2 and worse gastro-intestinal (GI) toxicity was reported in 3 % of patients at three months whilst grade 2 and worse genitourinary (GU) toxicity was 7 % at three months. There was a significant decrease in the median PSA at 12 months. The results from both the EQ-5D-5L data and EORTC global health status scale indicate a decline in the quality of life (QoL) during the first six months. The mean change in score for the EORTC scale showed a decrease of 11.4 points, which is considered clinically important. QoL improved back to baseline by 24 months. Worsening of hormonal symptoms in the first six months was reported with a return to baseline by 24 months and sexual activity in all men worsened in the first three months and returned to baseline at 12 months. Conclusion This study establishes the feasibility of online-MRIgRT for localised prostate on a 1.5 T MR-Linac with low rates of toxicity, similar to that published in the literature. However, the clinical benefits of MRIgRT over conventional radiotherapy in the setting of moderate hypofractionation is not evident. Further research will focus on the delivery of ultrahypofractionated regimens, where the potential advantages of MRIgRT for prostate cancer may become more discernible.
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Affiliation(s)
- Kobika Sritharan
- The Royal Marsden NHS Foundation Trust, UK
- The Institute of Cancer Research, UK
| | - Lois Daamen
- Division of Imaging and Oncology, University Medical Center Utrecht, Utrecht, the Netherlands
| | | | | | - Floris Pos
- The Netherlands Cancer Institute, The Netherlands
| | - Ananya Choudhury
- Division of Cancer Sciences, University of Manchester and The Christie NHS Foundation Trust, UK
| | | | | | | | - Emma Hall
- The Institute of Cancer Research, UK
| | - Helena M. Verkooijen
- Division of Imaging and Oncology, University Medical Center Utrecht, Utrecht, the Netherlands
| | | | | | - Adam Mitchell
- The Royal Marsden NHS Foundation Trust, UK
- The Institute of Cancer Research, UK
| | - Alison C. Tree
- The Royal Marsden NHS Foundation Trust, UK
- The Institute of Cancer Research, UK
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Snyder J, Smith B, Aubin JS, Shepard A, Hyer D. Simulating an intra-fraction adaptive workflow to enable PTV margin reduction in MRIgART volumetric modulated arc therapy for prostate SBRT. Front Oncol 2024; 13:1325105. [PMID: 38260830 PMCID: PMC10800949 DOI: 10.3389/fonc.2023.1325105] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Key Words] [Track Full Text] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/20/2023] [Accepted: 12/18/2023] [Indexed: 01/24/2024] Open
Abstract
Purpose This study simulates a novel prostate SBRT intra-fraction re-optimization workflow in MRIgART to account for prostate intra-fraction motion and evaluates the dosimetric benefit of reducing PTV margins. Materials and methods VMAT prostate SBRT treatment plans were created for 10 patients using two different PTV margins, one with a 5 mm margin except 3 mm posteriorly (standard) and another using uniform 2 mm margins (reduced). All plans were prescribed to 36.25 Gy in 5 fractions and adapted onto each daily MRI dataset. An intra-fraction adaptive workflow was simulated for the reduced margin group by synchronizing the radiation delivery with target position from cine MRI imaging. Intra-fraction delivered dose was reconstructed and prostate DVH metrics were evaluated under three conditions for the reduced margin plans: Without motion compensation (no-adapt), with a single adapt prior to treatment (ATP), and lastly for intra-fraction re-optimization during delivery (intra). Bladder and rectum DVH metrics were compared between the standard and reduced margin plans. Results As expected, rectum V18 Gy was reduced by 4.4 ± 3.9%, D1cc was reduced by 12.2 ± 6.8% (3.4 ± 2.3 Gy), while bladder reductions were 7.8 ± 5.6% for V18 Gy, and 9.6 ± 7.3% (3.4 ± 2.5 Gy) for D1cc for the reduced margin reference plans compared to the standard PTV margin. For the intrafraction replanning approach, average intra-fraction optimization times were 40.0 ± 2.9 seconds, less than the time to deliver one of the four VMAT arcs (104.4 ± 9.3 seconds) used for treatment delivery. When accounting for intra-fraction motion, prostate V36.25 Gy was on average 96.5 ± 4.0%, 99.1 ± 1.3%, and 99.6 ± 0.4 for the non-adapt, ATP, and intra-adapt groups, respectively. The minimum dose received by the prostate was less than 95% of the prescription dose in 84%, 36%, and 10% of fractions, for the non-adapt, ATP, and intra-adapt groups, respectively. Conclusions Intra-fraction re-optimization improves prostate coverage, specifically the minimum dose to the prostate, and enables PTV margin reduction and subsequent OAR sparing. Fast re-optimizations enable uninterrupted treatment delivery.
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Affiliation(s)
- Jeffrey Snyder
- Department of Radiation Oncology, University of Iowa Hospitals and Clinics, Iowa City, IA, United States
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Riis HL, Christiansen RL, Tilly N, Tilly D. Dosimetric validation of the couch and coil model for high-field MR-linac treatment planning. Z Med Phys 2023; 33:567-577. [PMID: 36990882 PMCID: PMC10751701 DOI: 10.1016/j.zemedi.2023.02.002] [Citation(s) in RCA: 1] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/11/2022] [Revised: 02/01/2023] [Accepted: 02/09/2023] [Indexed: 03/29/2023]
Abstract
PURPOSE The precision of the dose delivery in radiation therapy with high-field MR-linacs is challenging due to the substantial variation in the beam attenuation of the patient positioning system (PPS) (the couch and coils) as a function of the gantry angle. This work aimed to compare the attenuation of two PPSs located at two different MR-linac sites through measurements and calculations in the treatment planning system (TPS). METHODS Attenuation measurements were performed at every 1° gantry angle at the two sites with a cylindrical water phantom with a Farmer chamber inserted along the rotational axis of the phantom. The phantom was positioned with the chamber reference point (CRP) at the MR-linac isocentre. A compensation strategy was applied to minimise sinusoidal measurement errors due to, e.g. air cavity or setup. A series of tests were performed to assess the sensitivity to measurement uncertainties. The dose to a model of the cylindrical water phantom with the PPS added was calculated in the TPS (Monaco v5.4 as well as in a development version Dev of an upcoming release), for the same gantry angles as for the measurements. The TPS PPS model dependency of the dose calculation voxelisation resolution was also investigated. RESULTS A comparison of the measured attenuation of the two PPSs yielded differences of less than 0.5% for most gantry angles. The maximum deviation between the attenuation measurements for the two different PPSs exceeded ±1% at two specific gantry angles 115° and 245°, where the beam traverses the most complex PPS structures. The attenuation increases from 0% to 25% in 15° intervals around these angles. The measured and calculated attenuation, as calculated in v5.4, was generally within 1-2% with a systematic overestimation of the attenuation for gantry angles around 180°, as well as a maximum error of 4-5% for a few discrete angles in 10° gantry angle intervals around the complex PPS structures. The PPS modelling was improved compared to v5.4 in Dev, especially around 180°, and the results of those calculations were within ±1%, but with a similar 4% maximum deviation for the most complex PPS structures. CONCLUSIONS Generally, the two tested PPS structures exhibit very similar attenuation as a function of the gantry angle, including the angles with a steep change in attenuation. Both TPS versions, v5.4 and Dev delivered clinically acceptable accuracy of the calculated dose, as the differences in the measurements were overall better than ±2%. Additionally, Dev improved the accuracy of the dose calculation to ±1% for gantry angles around 180°.
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Affiliation(s)
- Hans Lynggaard Riis
- Odense University Hospital, Department of Oncology, Odense, Denmark; University of Southern Denmark, Department of Clinical Research, Odense, Denmark.
| | - Rasmus Lübeck Christiansen
- Odense University Hospital, Department of Oncology, Odense, Denmark; University of Southern Denmark, Department of Clinical Research, Odense, Denmark
| | - Nina Tilly
- Medical Radiation Physics, Department of Immunology, Genetics and Pathology, Uppsala University, Uppsala, Sweden; Elekta Instrument AB, Stockholm, Sweden
| | - David Tilly
- Medical Radiation Physics, Department of Immunology, Genetics and Pathology, Uppsala University, Uppsala, Sweden; Elekta Instrument AB, Stockholm, Sweden; Medical Physics, Akademiska Sjukhuset, Uppsala, Sweden
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Alexander SE, McNair HA, Oelfke U, Huddart R, Murray J, Pathmanathan A, Patel P, Sritharan K, van As N, Tree AC. Prostate Volume Changes during Extreme and Moderately Hypofractionated Magnetic Resonance Image-guided Radiotherapy. Clin Oncol (R Coll Radiol) 2022; 34:e383-e391. [PMID: 35469741 DOI: 10.1016/j.clon.2022.03.022] [Citation(s) in RCA: 11] [Impact Index Per Article: 5.5] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/24/2021] [Revised: 03/04/2022] [Accepted: 03/30/2022] [Indexed: 11/16/2022]
Abstract
AIMS Prostate morphological changes during external beam radiotherapy are poorly understood. Excellent soft-tissue visualisation offered by magnetic resonance image-guided radiotherapy (MRIgRT) provides an opportunity to better understand such changes. The aim of this study was to quantify prostate volume and dimension changes occurring during extreme and moderately hypofractionated schedules. MATERIALS AND METHODS Forty prostate cancer patients treated on the Unity 1.5 Tesla magnetic resonance linear accelerator (MRL) were retrospectively reviewed. The cohort comprised patients treated with 36.25 Gy in five fractions (n = 20) and 60 Gy in 20 fractions (n = 20). The volume of the delineated prostates on reference planning computed tomography (fused with MRI) and daily T2-weighted 2-min session images acquired on Unity were charted. Forty planning computed tomography and 500 MRL prostate volumes were evaluated. The mean absolute and relative change in prostate volume during radiotherapy was compared using a paired t-test (P value <0.01 considered significant to control for multiple comparisons). The maximum dimension of the delineated prostate was measured in three isocentric planes. RESULTS Significant prostate volume changes, relative to MRL imaging fraction 1 (MRL#1), were seen at all time points for the five-fraction group. The peak mean relative volume increase was 21% (P < 0.001), occurring at MRL#3 and MRL#4 after 14.5 and 21.75 Gy, respectively. Prostate expansion was greatest in the superior-inferior direction; the peak mean maximal extension was 5.9 mm. The maximal extension in the left-right and anterior-posterior directions measured 1.1 and 2.2 mm, respectively. For the 20-fraction group, prostate volume increased relative to MRL#1, for all treatment time points. The mean relative volume increase was 11% (P < 0.001) at MRL#5 after 12 Gy, it then fluctuated between 8 and 13%. From MRL#5 to MRL#20, the volume increase was significant (P < 0.01) for 12 of 16 time points calculated. The peak mean maximal extension in the superior-inferior direction was 3.1 mm. The maximal extension in the left-right and anterior-posterior directions measured 1.7 and 3.7 mm, respectively. CONCLUSION Significant prostate volume and dimension changes occur during extreme and moderately hypofractionated radiotherapy. The extent of change was greater during extreme hypofractionation. MRIgRT offers the opportunity to reveal, quantify and correct for this deformation.
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Affiliation(s)
- S E Alexander
- The Royal Marsden NHS Foundation Trust, Sutton, UK; The Institute of Cancer Research, London, UK.
| | - H A McNair
- The Royal Marsden NHS Foundation Trust, Sutton, UK; The Institute of Cancer Research, London, UK
| | - U Oelfke
- The Joint Department of Physics, The Royal Marsden Hospital and the Institute of Cancer Research, London, UK
| | - R Huddart
- The Royal Marsden NHS Foundation Trust, Sutton, UK; The Institute of Cancer Research, London, UK
| | - J Murray
- The Royal Marsden NHS Foundation Trust, Sutton, UK; The Institute of Cancer Research, London, UK
| | - A Pathmanathan
- The Royal Marsden NHS Foundation Trust, Sutton, UK; The Institute of Cancer Research, London, UK
| | - P Patel
- The Royal Marsden NHS Foundation Trust, Sutton, UK; The Institute of Cancer Research, London, UK
| | - K Sritharan
- The Royal Marsden NHS Foundation Trust, Sutton, UK; The Institute of Cancer Research, London, UK
| | - N van As
- The Royal Marsden NHS Foundation Trust, Sutton, UK; The Institute of Cancer Research, London, UK
| | - A C Tree
- The Royal Marsden NHS Foundation Trust, Sutton, UK; The Institute of Cancer Research, London, UK
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Stanescu T, Shessel A, Carpino-Rocca C, Taylor E, Semeniuk O, Li W, Barry A, Lukovic J, Dawson L, Hosni A. MRI-Guided Online Adaptive Stereotactic Body Radiation Therapy of Liver and Pancreas Tumors on an MR-Linac System. Cancers (Basel) 2022; 14:cancers14030716. [PMID: 35158984 PMCID: PMC8833602 DOI: 10.3390/cancers14030716] [Citation(s) in RCA: 15] [Impact Index Per Article: 7.5] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/20/2021] [Revised: 01/24/2022] [Accepted: 01/25/2022] [Indexed: 02/06/2023] Open
Abstract
Simple Summary The hybrid magnetic resonance imaging and medical linear accelerator (MR-Linac) systems are expected to revolutionize radiation therapy, uniquely offering high quality soft-tissue contrast and fast imaging to facilitate the online re-planning and guidance of the treatment delivery. While the clinical procedures for stereotactic body radiotherapy are well-established for conventional linacs (with their strengths and weaknesses), they still require significant development and refinement for the MR-Linac systems. Adjustment of fractionation schemes including clinical goals, patient selection, organ motion management, treatment session length, staff logistics, and overall complexity of the online re-planning sessions are key factors that drive the adoption of MR-Linac technologies. In this report, we present the clinical implementation of an MRI-guided radiation therapy workflow, which was used to treat 16 upper gastro-intestinal cancer patients on a 1.5 T MR-Linac platform. The workflow was proven to be feasible for a wide range of clinical scenarios, and the overall treatment session time was significantly reduced as tasks were optimized and the clinical team gradually gained expertise. Abstract Purpose: To describe a comprehensive workflow for MRI-guided online adaptive stereotactic body radiation therapy (SBRT) specific to upper gastrointestinal cancer patients with abdominal compression on a 1.5T MR-Linac system. Additionally, we discuss the workflow’s clinical feasibility and early experience in the case of 16 liver and pancreas patients. Methods: Eleven patients with liver cancer and five patients with pancreas cancer were treated with online adaptive MRI-guidance under abdominal compression. Two liver patients received single-fraction treatments; the remainder plus all pancreas cancer patients received five fractions. A total of 65 treatment sessions were investigated to provide analytics relevant to the online adaptive processes. The quantification of target and organ motion as well as definition and validation of internal target volume (ITV) margins were performed via multi-contrast imaging provided by three different 2D cine sequences. The plan generation was driven by full re-optimization strategies and using T2-weighted 3D image series acquired by means of a respiratory-triggered exhale phase or a time-averaged imaging protocol. As a pre-requisite for the clinical development of the procedure, the image quality was thoroughly investigated via phantom measurements and numerical simulations specific to upper abdominal sites. The delivery of the online adaptive treatments was facilitated by real-time monitoring with 2D cine imaging. Results: Liver 1-fraction and 5-fraction online adaptive session time were on average 80 and 67.5 min, respectively. The total session length varied between 70–90 min for a single fraction and 55–90 min for five fractions. The pancreas sessions were 54–85 min long with an average session time of 68.2 min. Target visualization on the 2D cine image data varied per patient, with at least one of the 2D cine sequences providing sufficient contrast to confidently identify its location and confirm reproducibility of ITV margins. The mean/range of absolute and relative dose values for all treatment sessions evaluated with ArcCheck were 90.6/80.9–96.1% and 99/95.4–100%, respectively. Conclusion: MR-guidance is feasible for liver and pancreas tumors when abdominal compression is used to reduce organ motion, improve imaging quality, and achieve a robust intra- and inter-fraction patient setup. However, the treatment length is significantly longer than for the conventional linac, and patient compliance is paramount for the successful completion of the treatment. Opportunities for reducing the online adaptive session time should be explored. As the next steps, dose-of-the-day and dose accumulation analysis and tools are needed to enhance the workflow and to help further refine the online re-planning processes.
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Affiliation(s)
- Teo Stanescu
- Princess Margaret Cancer Centre, University Health Network, Toronto, ON M5G 2M9, Canada; (A.S.); (C.C.-R.); (E.T.); (O.S.); (W.L.); (A.B.); (J.L.); (L.D.); (A.H.)
- Department of Radiation Oncology, University of Toronto, Toronto, ON M5T 1P5, Canada
- Department of Mechanical and Industrial Engineering, University of Toronto, Toronto, ON M5S 3G8, Canada
- Correspondence:
| | - Andrea Shessel
- Princess Margaret Cancer Centre, University Health Network, Toronto, ON M5G 2M9, Canada; (A.S.); (C.C.-R.); (E.T.); (O.S.); (W.L.); (A.B.); (J.L.); (L.D.); (A.H.)
| | - Cathy Carpino-Rocca
- Princess Margaret Cancer Centre, University Health Network, Toronto, ON M5G 2M9, Canada; (A.S.); (C.C.-R.); (E.T.); (O.S.); (W.L.); (A.B.); (J.L.); (L.D.); (A.H.)
| | - Edward Taylor
- Princess Margaret Cancer Centre, University Health Network, Toronto, ON M5G 2M9, Canada; (A.S.); (C.C.-R.); (E.T.); (O.S.); (W.L.); (A.B.); (J.L.); (L.D.); (A.H.)
- Department of Radiation Oncology, University of Toronto, Toronto, ON M5T 1P5, Canada
| | - Oleksii Semeniuk
- Princess Margaret Cancer Centre, University Health Network, Toronto, ON M5G 2M9, Canada; (A.S.); (C.C.-R.); (E.T.); (O.S.); (W.L.); (A.B.); (J.L.); (L.D.); (A.H.)
| | - Winnie Li
- Princess Margaret Cancer Centre, University Health Network, Toronto, ON M5G 2M9, Canada; (A.S.); (C.C.-R.); (E.T.); (O.S.); (W.L.); (A.B.); (J.L.); (L.D.); (A.H.)
| | - Aisling Barry
- Princess Margaret Cancer Centre, University Health Network, Toronto, ON M5G 2M9, Canada; (A.S.); (C.C.-R.); (E.T.); (O.S.); (W.L.); (A.B.); (J.L.); (L.D.); (A.H.)
- Department of Radiation Oncology, University of Toronto, Toronto, ON M5T 1P5, Canada
| | - Jelena Lukovic
- Princess Margaret Cancer Centre, University Health Network, Toronto, ON M5G 2M9, Canada; (A.S.); (C.C.-R.); (E.T.); (O.S.); (W.L.); (A.B.); (J.L.); (L.D.); (A.H.)
- Department of Radiation Oncology, University of Toronto, Toronto, ON M5T 1P5, Canada
| | - Laura Dawson
- Princess Margaret Cancer Centre, University Health Network, Toronto, ON M5G 2M9, Canada; (A.S.); (C.C.-R.); (E.T.); (O.S.); (W.L.); (A.B.); (J.L.); (L.D.); (A.H.)
- Department of Radiation Oncology, University of Toronto, Toronto, ON M5T 1P5, Canada
| | - Ali Hosni
- Princess Margaret Cancer Centre, University Health Network, Toronto, ON M5G 2M9, Canada; (A.S.); (C.C.-R.); (E.T.); (O.S.); (W.L.); (A.B.); (J.L.); (L.D.); (A.H.)
- Department of Radiation Oncology, University of Toronto, Toronto, ON M5T 1P5, Canada
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Andreozzi JM, Brůža P, Cammin J, Alexander DA, Pogue BW, Green O, Gladstone DJ. Optical emission-based phantom to verify coincidence of radiotherapy and imaging isocenters on an MR-linac. J Appl Clin Med Phys 2021; 22:252-261. [PMID: 34409766 PMCID: PMC8425893 DOI: 10.1002/acm2.13377] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/07/2020] [Revised: 05/03/2021] [Accepted: 07/09/2021] [Indexed: 11/15/2022] Open
Abstract
Purpose Demonstrate a novel phantom design using a remote camera imaging method capable of concurrently measuring the position of the x‐ray isocenter and the magnetic resonance imaging (MRI) isocenter on an MR‐linac. Methods A conical frustum with distinct geometric features was machined out of plastic. The phantom was submerged in a small water tank, and aligned using room lasers on a MRIdian MR‐linac (ViewRay Inc., Cleveland, OH). The phantom physical isocenter was visualized in the MR images and related to the DICOM coordinate isocenter. To view the x‐ray isocenter, an intensified CMOS camera system (DoseOptics LLC., Hanover, NH) was placed at the foot of the treatment couch, and centered such that the optical axis of the camera was coincident with the central axis of the treatment bore. Two or four 8.3mm x 24.1cm beams irradiated the phantom from cardinal directions, producing an optical ring on the conical surface of the phantom. The diameter of the ring, measured at the peak intensity, was compared to the known diameter at the position of irradiation to determine the Z‐direction offset of the beam. A star‐shot method was employed on the front face of the frustum to determine X‐Y alignment of the MV beam. Known shifts were applied to the phantom to establish the sensitivity of the method. Results Couch translations, demonstrative of possible isocenter misalignments, on the order of 1mm were detectable for both the radiotherapy and MRI isocenters. Data acquired on the MR‐linac demonstrated an average error of 0.28mm(N=10, R2=0.997, σ=0.37mm) in established Z displacement, and 0.10mm(N=5, σ=0.34mm) in XY directions of the radiotherapy isocenter. Conclusions The phantom was capable of measuring both the MRI and radiotherapy treatment isocenters. This method has the potential to be of use in MR‐linac commissioning, and could be streamlined to be valuable in daily constancy checks of isocenter coincidence.
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Affiliation(s)
- Jacqueline M Andreozzi
- Thayer School of Engineering, Dartmouth College, Hanover, New Hampshire, USA.,Department of Radiation Oncology, Moffitt Cancer Center, Tampa, Florida, USA
| | - Petr Brůža
- Thayer School of Engineering, Dartmouth College, Hanover, New Hampshire, USA
| | - Jochen Cammin
- Department of Radiation Oncology, Washington University School of Medicine, St. Louis, Missouri, USA
| | - Daniel A Alexander
- Thayer School of Engineering, Dartmouth College, Hanover, New Hampshire, USA
| | - Brian W Pogue
- Thayer School of Engineering and Department of Physics and Astronomy, Dartmouth College, Hanover, New Hampshire, USA
| | - Olga Green
- Department of Radiation Oncology, Washington University School of Medicine, St. Louis, Missouri, USA
| | - David J Gladstone
- Norris Cotton Cancer Center, Dartmouth-Hitchcock Medical Center, Lebanon, New Hampshire, USA.,Geisel School of Medicine, Thayer School of Engineering, Dartmouth College, Hanover, New Hampshire, USA
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Affiliation(s)
- Sangjune Laurence Lee
- Department of Human Oncology, University of Wisconsin Hospital and Clinics, Madison, WI, USA
- Department of Oncology, Division of Radiation Oncology, University of Calgary, Calgary, AB, Canada
| | - William A. Hall
- Department of Radiation Oncology, Medical College of Wisconsin, Milwaukee, WI, USA
| | - Zachary S. Morris
- Department of Human Oncology, University of Wisconsin Hospital and Clinics, Madison, WI, USA
| | - Leslie Christensen
- University of Wisconsin School of Medicine and Public Health, Madison, WI, USA
| | - Michael Bassetti
- Department of Human Oncology, University of Wisconsin Hospital and Clinics, Madison, WI, USA
- Corresponding author. Department of Human Oncology, University of Wisconsin, University Hospital L7/B36, 600 Highland Avenue, Madison, WI 53792.
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Keesman R, van der Bijl E, Janssen TM, Vijlbrief T, Pos FJ, van der Heide UA. Clinical workflow for treating patients with a metallic hip prosthesis using magnetic resonance imaging-guided radiotherapy. Phys Imaging Radiat Oncol 2021; 15:85-90. [PMID: 33458331 PMCID: PMC7807622 DOI: 10.1016/j.phro.2020.07.010] [Citation(s) in RCA: 4] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Subscribe] [Scholar Register] [Received: 02/28/2020] [Revised: 07/16/2020] [Accepted: 07/24/2020] [Indexed: 12/25/2022]
Abstract
Background & purpose Metallic prostheses distort the magnetic field during magnetic resonance imaging (MRI), leading to geometric distortions and signal loss. The purpose of this work was to develop a method to determine eligibility for MRI-guided radiotherapy (MRIgRT) on a per patient basis by estimating the magnitude of geometric distortions inside the clinical target volume (CTV). Materials & methods Three patients with prostate cancer and hip prosthesis, treated using MRIgRT, were included. Eligibility for MRIgRT was based on computed tomography and associated CTV delineations, together with a field-distortion (B0) map and anatomical images acquired during MR simulation. To verify the method, B0 maps made during MR simulation and each MRIgRT treatment fraction were compared. Results Estimates made during MR simulation of the magnitude of distortions inside the CTV were 0.43 mm, 0.19 mm and 2.79 mm compared to the average over all treatment fractions of 1.40 mm, 0.32 mm and 1.81 mm, per patient respectively. Conclusions B0 map acquisitions prior to treatment can be used to estimate the magnitude of distortions during MRIgRT to guide the decision on eligibility for MRIgRT of prostate cancer patients with metallic hip implants.
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Affiliation(s)
- Rick Keesman
- Department of Radiation Oncology, Netherlands Cancer Institute, Plesmanlaan 121, 1066CX Amsterdam, The Netherlands
| | - Erik van der Bijl
- Department of Radiation Oncology, Netherlands Cancer Institute, Plesmanlaan 121, 1066CX Amsterdam, The Netherlands
| | - Tomas M Janssen
- Department of Radiation Oncology, Netherlands Cancer Institute, Plesmanlaan 121, 1066CX Amsterdam, The Netherlands
| | - Tineke Vijlbrief
- Department of Radiation Oncology, Netherlands Cancer Institute, Plesmanlaan 121, 1066CX Amsterdam, The Netherlands
| | - Floris J Pos
- Department of Radiation Oncology, Netherlands Cancer Institute, Plesmanlaan 121, 1066CX Amsterdam, The Netherlands
| | - Uulke A van der Heide
- Department of Radiation Oncology, Netherlands Cancer Institute, Plesmanlaan 121, 1066CX Amsterdam, The Netherlands
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Darafsheh A, Hao Y, Maraghechi B, Cammin J, Reynoso FJ, Khan R. Influence of 0.35 T magnetic field on the response of EBT3 and EBT-XD radiochromic films. Med Phys 2020; 47:4543-4552. [PMID: 32502280 DOI: 10.1002/mp.14313] [Citation(s) in RCA: 6] [Impact Index Per Article: 1.5] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/07/2020] [Revised: 05/26/2020] [Accepted: 05/27/2020] [Indexed: 11/07/2022] Open
Abstract
PURPOSE To investigate the inconsistency of recent literature on the effect of magnetic field on the response of radiochromic films, we studied the influence of 0.35 T magnetic field on dosimetric response of EBT3 and EBT-XD GafchromicTM films. METHODS Two different models of radiochromic films, EBT3 and EBT-XD, were investigated. Pieces of films samples from two different batches for each model were irradiated at different dose levels ranging from 1 to 20 Gy using 6 MV flattening filter free (FFF) x-rays generated by a clinical MR-guided radiotherapy system (B = 0.35 T). Film samples from the same batch were irradiated at corresponding dose levels using 6 MV FFF beam from a conventional linac (B = 0) for comparison. The net optical density was measured 48 h postirradiation using a flatbed scanner. The absorbance spectra were also measured over 500-700 nm wavelength range using a fiber-coupled spectrometer with 2.5 nm resolution. To study the effect of fractionated dose delivery to EBT3 (/EBT-XD) films, 8 (/16) Gy dose was delivered in four 2 (/4) Gy fractions with 24 h interval between fractions. RESULTS No significant difference was found in the net optical density and net absorbance of the films irradiated with or without the presence of magnetic field. No dependency on the orientation of the film during irradiation with respect to the magnetic field was observed. The fractionated dose delivery resulted in the same optical density as delivering the whole dose in a single fraction. CONCLUSIONS The 0.35 T magnetic field employed in the ViewRay® MR-guided radiotherapy system did not show any significant influence on the response of EBT3 and EBT-XD GafchromicTM films.
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Affiliation(s)
- Arash Darafsheh
- Department of Radiation Oncology, Washington University School of Medicine, St. Louis, MO, 63110, USA
| | - Yao Hao
- Department of Radiation Oncology, Washington University School of Medicine, St. Louis, MO, 63110, USA
| | - Borna Maraghechi
- Department of Radiation Oncology, Washington University School of Medicine, St. Louis, MO, 63110, USA
| | - Jochen Cammin
- Department of Radiation Oncology, Washington University School of Medicine, St. Louis, MO, 63110, USA
| | - Francisco J Reynoso
- Department of Radiation Oncology, Washington University School of Medicine, St. Louis, MO, 63110, USA
| | - Rao Khan
- Department of Radiation Oncology, Washington University School of Medicine, St. Louis, MO, 63110, USA
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10
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Lim-Reinders S, Keller BM, Sahgal A, Chugh B, Kim A. Measurement of surface dose in an MR-Linac with optically stimulated luminescence dosimeters for IMRT beam geometries. Med Phys 2020; 47:3133-3142. [PMID: 32302010 DOI: 10.1002/mp.14185] [Citation(s) in RCA: 3] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/12/2019] [Revised: 03/24/2020] [Accepted: 04/01/2020] [Indexed: 12/31/2022] Open
Abstract
PURPOSE This study aims to measure the surface dose on an anthropomorphic phantom for intensity-modulated radiation therapy (IMRT) plans treated in a 1.5 T magnetic resonance (MR)-Linac. Previous studies have used Monte Carlo programs to simulate surface dose and have recognized high surface dose as a potential limiting factor for the MR-Linac; however, to our knowledge surface dose measurement for clinical plans has not yet been published. Given the novelty of the MR-Linac, it is important to perform in vivo measurements of a potentially dose-limiting factor such as surface dose when moving forward for clinical use. METHODS Optically stimulated luminescence dosimeters (OSLDs) were used on an anthropomorphic phantom. Intensity-modulated radiation therapy plans were generated to treat a near-surface breast tumor in the phantom. The tumor was treated with 2, 3, 5, 7, and 9 beam IMRT plans with a 1.5 T MR-Linac using a 7-MV photon beam. The plans were generated in a Monte Carlo treatment planning system (TPS) capable of modeling magnetic field effects. The surface dose was sampled in seven locations on the surface surrounding the planning target volume (PTV), and in two different OSLD configurations with the dosimeters measuring water equivalent depths of 0.16 and 0.64 mm. The TPS was used to estimate the doses at the OSLD locations. In addition, MR images were taken of a pork belly with and without an OSLD placed anteriorly placed to determine the effect of an OSLD on image fidelity. RESULTS For the 3, 5, 7, and 9-beam configurations, surface doses were approximately half that of the prescription dose to the simulated tumor, although the magnitude of the skin dose relative to the prescription is certainly also dependent on individual patient anatomy. The general trend for both TPS and measurements was that the greater the number of beams, the lower the skin doses and dose readings; also, with increasing numbers of beams, doses at shallow depths become lower relative to deeper depths. The MR images showed that the presence of the OSLD did not induce clinically relevant geometric distortions or intensity differences. CONCLUSIONS To our knowledge, this study is the first of its kind to experimentally measure the surface dose in an MR-Linac for IMRT plans. This study has explored the use of OSLDs to measure in vivo surface dose in a clinical setting. OSLDs may be used to measure skin dose clinically when there are concerns of skin radiation burns and near-surface toxicity. Optically stimulated luminescence dosimeters are promising devices for in vivo surface dosimetry in an MR-Linac.
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Affiliation(s)
- Stephanie Lim-Reinders
- Sunnybrook Health Sciences Centre/Odette Cancer Centre, 2075 Bayview Ave, Toronto, ON, M4N 3M5, Canada.,Faculty of Medicine, Medical Sciences Building, University of Toronto, 1 King's College Circle, Toronto, ON, M5S 1A8, Canada
| | - Brian M Keller
- Faculty of Medicine, Medical Sciences Building, University of Toronto, 1 King's College Circle, Toronto, ON, M5S 1A8, Canada.,Department of Radiation Oncology, Faculty of Medicine, University of Toronto, 149 College Street, Suite 504, Toronto, ON, M5T 1P5, Canada
| | - Arjun Sahgal
- Faculty of Medicine, Medical Sciences Building, University of Toronto, 1 King's College Circle, Toronto, ON, M5S 1A8, Canada.,Department of Radiation Oncology, Faculty of Medicine, University of Toronto, 149 College Street, Suite 504, Toronto, ON, M5T 1P5, Canada
| | - Brige Chugh
- Faculty of Medicine, Medical Sciences Building, University of Toronto, 1 King's College Circle, Toronto, ON, M5S 1A8, Canada.,Department of Radiation Oncology, Faculty of Medicine, University of Toronto, 149 College Street, Suite 504, Toronto, ON, M5T 1P5, Canada
| | - Anthony Kim
- Faculty of Medicine, Medical Sciences Building, University of Toronto, 1 King's College Circle, Toronto, ON, M5S 1A8, Canada.,Department of Radiation Oncology, Faculty of Medicine, University of Toronto, 149 College Street, Suite 504, Toronto, ON, M5T 1P5, Canada
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11
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Steinmann A, Alvarez P, Lee H, Court L. MRIgRT head and neck anthropomorphic QA phantom: Design, development, reproducibility, and feasibility study. Med Phys 2020; 47:604-613. [PMID: 31808949 PMCID: PMC7796776 DOI: 10.1002/mp.13951] [Citation(s) in RCA: 10] [Impact Index Per Article: 2.5] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/01/2019] [Revised: 10/21/2019] [Accepted: 10/22/2019] [Indexed: 12/29/2022] Open
Abstract
PURPOSE The purpose of this paper was to design, manufacture, and evaluate a tissue equivalent, dual magnetic resonance/computed tomography (MR/CT) visible anthropomorphic head and neck (H&N) phantom. This phantom was specially designed as an end-to-end quality assurance (QA) tool for MR imaging guided radiotherapy (MRIgRT) systems participating in NCI-sponsored clinical trials. METHOD The MRIgRT H&N phantom was constructed using a water-fillable acrylic shell and a custom insert that mimics an organ at risk (OAR) and target structures. The insert consists of a primary and secondary planning target volume (PTV) manufactured of a synthetic Clear Ballistic gel, an acrylic OAR and surrounding tissue fabricated using melted Superflab. Radiochromic EBT3 film and thermoluminescent detectors (TLDs) were used to measure the dose distribution and absolute dose, respectively. The phantom was evaluated by conducting an end-to-end test that included: imaging on a GE Lightspeed CT simulator, planning on Monaco treatment planning software (TPS), verifying treatment setup with MR, and irradiating on Elekta's 1.5 T Unity MR linac system. The phantom was irradiated three times using the same plan to determine reproducibility. Three institutions, equipped with either ViewRay MRIdian 60 Co or ViewRay MRIdian Linac, were used to conduct a feasibility study by performing independent end-to-end studies. Thermoluminescent detectors were evaluated in both reproducibility and feasibility studies by comparing ratios of measured TLD to reported TPS calculated values. Radiochromic film was used to compare measured planar dose distributions to expected TPS distributions. Film was evaluated by using an in-house gamma analysis software to measure the discrepancies between film and TPS. RESULTS The MRIgRT H&N phantom on the Unity system resulted in reproducible TLD doses (SD < 1.5%). The measured TLD to calculated dose ratios for the Unity system ranged from 0.94 to 0.98. The Viewray dose result comparisons had a larger range (0.95-1.03) but these depended on the TPS dose calculations from each site. Using a 7%/4 mm gamma analysis, Viewray institutions had average axial and sagittal passing rates of 97.3% and 96.2% and the Unity system had average passing rates of 97.8% and 89.7%, respectively. All of the results were within the Imaging and Radiation Oncology Core in Houston (IROC-Houston) standard credentialing criteria of 7% on TLDs, and >85% of pixels passing gamma analysis using 7%/4 mm on films. CONCLUSIONS An MRIgRT H&N phantom that is tissue equivalent and visible on both CT and MR was developed. The results from initial reproducibility and feasibility testing of the MRIgRT H&N phantom using the tested MGIgRT systems suggests the phantom's potential utility as a credentialing tool for NCI-clinical trials.
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Affiliation(s)
- A. Steinmann
- Department of Radiation Physics, The University of Texas M. D. Anderson Cancer Center, Houston, TX 77030, USA
| | - P. Alvarez
- Department of Radiation Physics, The University of Texas M. D. Anderson Cancer Center, Houston, TX 77030, USA
| | - H. Lee
- Department of Radiation Physics, The University of Texas M. D. Anderson Cancer Center, Houston, TX 77030, USA
| | - L. Court
- Department of Radiation Physics, The University of Texas M. D. Anderson Cancer Center, Houston, TX 77030, USA
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12
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Steinmann A, O'Brien D, Stafford R, Sawakuchi G, Wen Z, Court L, Fuller C, Followill D. Investigation of TLD and EBT3 performance under the presence of 1.5T, 0.35T, and 0T magnetic field strengths in MR/CT visible materials. Med Phys 2019; 46:3217-3226. [PMID: 30950071 DOI: 10.1002/mp.13527] [Citation(s) in RCA: 12] [Impact Index Per Article: 2.4] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/01/2018] [Revised: 12/17/2018] [Accepted: 12/17/2018] [Indexed: 11/09/2022] Open
Abstract
PURPOSE The aim of this study was to investigate thermoluminescent dosimeters (TLD) and radiochromic EBT3 film inside MR/CT visible geometric head and thorax phantoms in the presence of: 0, 0.35, and 1.5 T magnetic fields. METHODS Thermoluminescent Dosimeters reproducibility studies were examined by irradiating IROC-Houston's TLD acrylic block five times under 0 and 1.5 T configurations of Elekta's Unity system and three times under 0 and 0.35 T configurations of ViewRay's MRIdian Cobalt-60 (60 Co) system. Both systems were irradiated with an equivalent 10 × 10 cm2 field size, and a prescribed dose of 3 Gy to the maximum depth deposition (dmax). EBT3 film and TLDs were investigated using two geometrical Magnetic Resonance (MR)-guided Radiation Therapy (MRgRT) head and thorax phantoms. Each geometrical phantom had eight quadrants that combined to create a centrally located rectangular tumor (3 × 3 × 5 cm3 ) surrounded by tissue to form a 15 × 15 × 15 cm3 cubic phantom. Liquid polyvinyl chloride plastic and Superflab were used to simulate the tumor and surrounding tissue in the head phantom, respectively. Synthetic ballistic gel and a heterogeneous in-house mixture were used to construct the tumor and surrounding tissue in the thorax phantom, respectively. EBT3 and double-loaded TLDs were used in the phantoms to compare beam profiles and point dose measurements with and without magnetic fields. GEANT4 Monte Carlo simulations were performed to validate the detectors for both Unity 0 T/1.5 T and MRIdian 0 T/0.35 T configurations. RESULTS Average TLD block measurements which, compared the magnetic field effects (magnetic field vs 0 T) on the Unity and MRIdian systems, were 0.5% and 0.6%, respectively. The average ratios between magnetic field effects for the geometric thorax and head phantoms under the Unity system were -0.2% and 1.6% and for the MRIdian system were 0.2% and -0.3%, respectively. Beam profiles generated with both systems agreed with Monte Carlo measurements and previous literature findings. CONCLUSIONS TLDs and EBT3 film dosimeters could potentially be used in MR/CT visible tissue equivalent phantoms that will experience a magnetic field environment.
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Affiliation(s)
- A Steinmann
- Department of Radiation Physics, The University of Texas M.D. Anderson Cancer Center, Houston, TX, 77030, USA
| | - D O'Brien
- Department of Radiation Physics, The University of Texas M.D. Anderson Cancer Center, Houston, TX, 77030, USA
| | - R Stafford
- Department of Imaging Physics, The University of Texas M.D. Anderson Cancer Center, Houston, TX, 77030, USA
| | - G Sawakuchi
- Department of Radiation Physics, The University of Texas M.D. Anderson Cancer Center, Houston, TX, 77030, USA
| | - Z Wen
- Department of Radiation Physics, The University of Texas M.D. Anderson Cancer Center, Houston, TX, 77030, USA
| | - L Court
- Department of Radiation Physics, The University of Texas M.D. Anderson Cancer Center, Houston, TX, 77030, USA
| | - C Fuller
- Department of Radiation Oncology, The University of Texas M.D. Anderson Cancer Center, Houston, TX, 770304, USA
| | - D Followill
- Department of Radiation Physics, The University of Texas M.D. Anderson Cancer Center, Houston, TX, 77030, USA
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13
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Henke LE, Contreras JA, Green OL, Cai B, Kim H, Roach MC, Olsen JR, Fischer-Valuck B, Mullen DF, Kashani R, Thomas MA, Huang J, Zoberi I, Yang D, Rodriguez V, Bradley JD, Robinson CG, Parikh P, Mutic S, Michalski J. Magnetic Resonance Image-Guided Radiotherapy ( MRIgRT): A 4.5-Year Clinical Experience. Clin Oncol (R Coll Radiol) 2018; 30:720-727. [PMID: 30197095 PMCID: PMC6177300 DOI: 10.1016/j.clon.2018.08.010] [Citation(s) in RCA: 98] [Impact Index Per Article: 16.3] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/01/2018] [Revised: 07/19/2018] [Accepted: 08/21/2018] [Indexed: 10/28/2022]
Abstract
AIMS Magnetic resonance image-guided radiotherapy (MRIgRT) has been clinically implemented since 2014. This technology offers improved soft-tissue visualisation, daily imaging, and intra-fraction real-time imaging without added radiation exposure, and the opportunity for adaptive radiotherapy (ART) to adjust for anatomical changes. Here we share the longest single-institution experience with MRIgRT, focusing on trends and changes in use over the past 4.5 years. MATERIALS AND METHODS We analysed clinical information, including patient demographics, treatment dates, disease sites, dose/fractionation, and clinical trial enrolment for all patients treated at our institution using MRIgRT on a commercially available, integrated 0.35 T MRI, tri-cobalt-60 device from 2014 to 2018. For each patient, factors including disease site, clinical rationale for MRIgRT use, use of ART, and proportion of fractions adapted were summated and compared between individual years of use (2014-2018) to identify shifts in institutional practice patterns. RESULTS Six hundred and forty-two patients were treated with 666 unique treatment courses using MRIgRT at our institution between 2014 and 2018. Breast cancer was the most common disease, with use of cine MRI gating being a particularly important indication, followed by abdominal sites, where the need for cine gating and use of ART drove MRIgRT use. One hundred and ninety patients were treated using ART in 1550 fractions, 67.6% (1050) of which were adapted. ART was primarily used in cancers of the abdomen. Over time, breast and gastrointestinal cancers became increasingly dominant for MRIgRT use, hypofractionated treatment courses became more popular, and gastrointestinal cancers became the principal focus of ART. DISCUSSION MRIgRT is widely applicable within the field of radiation oncology and new clinical uses continue to emerge. At our institution to date, applications such as ART for gastrointestinal cancers and accelerated partial breast irradiation (APBI) for breast cancer have become dominant indications, although this is likely to continue to evolve.
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Affiliation(s)
- L E Henke
- Department of Radiation Oncology, Washington University School of Medicine, St. Louis, MO, USA
| | - J A Contreras
- Department of Radiation Oncology, Washington University School of Medicine, St. Louis, MO, USA
| | - O L Green
- Department of Radiation Oncology, Washington University School of Medicine, St. Louis, MO, USA
| | - B Cai
- Department of Radiation Oncology, Washington University School of Medicine, St. Louis, MO, USA
| | - H Kim
- Department of Radiation Oncology, Washington University School of Medicine, St. Louis, MO, USA
| | - M C Roach
- Department of Radiation Oncology, Washington University School of Medicine, St. Louis, MO, USA
| | - J R Olsen
- Department of Radiation Oncology, University of Colorado School of Medicine, Aurora, CO, USA
| | - B Fischer-Valuck
- Department of Radiation Oncology, Washington University School of Medicine, St. Louis, MO, USA
| | - D F Mullen
- Department of Radiation Oncology, Washington University School of Medicine, St. Louis, MO, USA
| | - R Kashani
- Department of Radiation Oncology, University of Michigan, Ann Arbor, MI, USA
| | - M A Thomas
- Department of Radiation Oncology, Washington University School of Medicine, St. Louis, MO, USA
| | - J Huang
- Department of Radiation Oncology, Washington University School of Medicine, St. Louis, MO, USA
| | - I Zoberi
- Department of Radiation Oncology, Washington University School of Medicine, St. Louis, MO, USA
| | - D Yang
- Department of Radiation Oncology, Washington University School of Medicine, St. Louis, MO, USA
| | - V Rodriguez
- Department of Radiation Oncology, Washington University School of Medicine, St. Louis, MO, USA
| | - J D Bradley
- Department of Radiation Oncology, Washington University School of Medicine, St. Louis, MO, USA
| | - C G Robinson
- Department of Radiation Oncology, Washington University School of Medicine, St. Louis, MO, USA
| | - P Parikh
- Department of Radiation Oncology, Washington University School of Medicine, St. Louis, MO, USA
| | - S Mutic
- Department of Radiation Oncology, Washington University School of Medicine, St. Louis, MO, USA
| | - J Michalski
- Department of Radiation Oncology, Washington University School of Medicine, St. Louis, MO, USA.
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14
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O'Brien DJ, Dolan J, Pencea S, Schupp N, Sawakuchi GO. Relative dosimetry with an MR-linac: Response of ion chambers, diamond, and diode detectors for off-axis, depth dose, and output factor measurements. Med Phys 2017; 45:884-897. [PMID: 29178457 DOI: 10.1002/mp.12699] [Citation(s) in RCA: 42] [Impact Index Per Article: 6.0] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/01/2017] [Revised: 11/16/2017] [Accepted: 11/21/2017] [Indexed: 11/08/2022] Open
Abstract
PURPOSE The purpose of this study was to acquire beam data for an MR-linac, with and without a 1.5 T magnetic field, by using a variety of commercially available detectors to assess their relative response in the magnetic field. The impact of the magnetic field on the measured dose distribution was also assessed. METHODS An MR-safe 3D scanning water phantom was used to measure output factors, depth dose curves, and off-axis profiles for various depths and for field sizes between 2 × 2 cm2 and 22 × 22 cm2 for an Elekta MR-linac beam with the orthogonal 1.5 T magnetic field on or off. An on-board MV portal imaging system was used to ensure that the reproducibility of the detector position, both with and without the magnetic field, was within 0.1 mm. The detectors used included ionization chambers with large, medium, and small sensitive volumes; a diamond detector; a shielded diode; and an unshielded diode. RESULTS The offset of the effective point of measurement of the ionization chambers was found to be reduced by at least half for each chamber in the direction parallel with the beam. A lateral shift of similar magnitude was also introduced to the chambers' effective point of measurement toward the average direction of the Lorentz force. A similar lateral shift (but in the opposite direction) was also observed for the diamond and diode detectors. The measured lateral shift in the dose distribution was independent of depth and field size for each detector for fields between 2 × 2 cm2 and 10 × 10 cm2 . The shielded diode significantly misrepresented the dose distribution in the lateral direction perpendicular to the magnetic field, making it seem more symmetric. The percentage depth dose was generally found to be lower with the magnetic field than without, but this difference was reduced as field size increased. The depth of maximum dose showed little dependence on field size in the presence of the magnetic field, with values from 1.2 cm to 1.3 cm between the 2 × 2 cm2 and 22 × 22 cm2 fields. Output factors measured in the magnetic field at the center of the beam profile produced a larger spread of values between detectors for fields smaller than 10 × 10 cm2 (with a spread of 2% at 3 × 3 cm2 ). The spread of values was more consistent when the output factors were measured at the point of peak intensity of the lateral dose distribution instead (except for the shielded diode which differed by up to 2% depending on field size). CONCLUSIONS The magnetic field of the MR-linac alters the effective point of measurement of ionization chambers, shifting it both downstream and laterally. Shielded diodes produce incorrect and misleading dose profiles. The output factor measured at the point of peak intensity in the lateral dose distribution is more robust than the conventional output factor (measured at central axis). Diodes are not recommended for output factor measurements in the magnetic field.
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Affiliation(s)
- Daniel J O'Brien
- Department of Radiation Physics, The University of Texas MD Anderson Cancer Center, Houston, TX, 77030, USA
| | - James Dolan
- Elekta Software, Elekta A. B., Maryland Heights, MO, 63043, USA
| | - Stefan Pencea
- Elekta Software, Elekta A. B., Maryland Heights, MO, 63043, USA
| | - Nicholas Schupp
- Elekta Software, Elekta A. B., Maryland Heights, MO, 63043, USA
| | - Gabriel O Sawakuchi
- Department of Radiation Physics, The University of Texas MD Anderson Cancer Center, Houston, TX, 77030, USA.,Graduate School of Biomedical Sciences, The University of Texas, Houston, TX, 77030, USA
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O'Brien DJ, Sawakuchi GO. Monte Carlo study of the chamber-phantom air gap effect in a magnetic field. Med Phys 2017; 44:3830-3838. [PMID: 28432792 DOI: 10.1002/mp.12290] [Citation(s) in RCA: 40] [Impact Index Per Article: 5.7] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/02/2016] [Revised: 03/02/2017] [Accepted: 04/15/2017] [Indexed: 11/07/2022] Open
Abstract
PURPOSE The aim of this study was to examine the effect of submillimeter air gaps that may exist between an ionization chamber and solid phantoms when measurements are performed in a magnetic field. METHODS Geant4 Monte Carlo simulations were performed using a model of a PTW 30013 Farmer chamber in a water phantom. Symmetrical and asymmetrical air gaps of various thicknesses were modeled surrounding the chamber, and the dose to the air cavity of the chamber was scored in each case. Magnetic fields were modeled parallel to the long axis of the chamber with strengths of 0, 0.35 T, 1.0 T, and 1.5 T. To examine the phenomenon in more detail, the gyroradii of the electrons responsible for the energy deposited in the chamber were scored as they entered the chamber and the total energy deposited was split into three components: energy originating from inside the chamber, in the immediate vacinity of the chamber, or outside the chamber. RESULTS Differences in the chamber dose of 1.6% were observed for asymmetric air gaps just 0.2 mm thick. No effect greater than 0.5% was observed for the symmetrical air gaps investigated in this work (1.4 mm thick or less) for this chamber/magnetic field configuration. The mean gyroradius of contributing electrons as they first enter the chamber was 4 mm. The presence of the air gap reduced the energy contributions from electrons released in the immediate vicinity of the chamber, and this loss was not completely compensated for when a magnetic field was present. CONCLUSIONS The gyroradius of most electrons was too large to be responsible for the air gap effect via the electron return effect; instead, the effect is attributed to the loss of energy contributions from electrons originating inside the air gap volume, which is not completely compensated for by more distant electrons owing to their reduced range in the magnetic field. When the chamber is parallel with the magnetic field, symmetric air gaps have a smaller effect (< 0.5%) compared to asymmetric air-gaps (up to 1.6%) on the chamber response.
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Affiliation(s)
- Daniel J O'Brien
- Department of Radiation Physics, The University of Texas MD Anderson Cancer Center, Houston, TX, 77030, USA
| | - Gabriel O Sawakuchi
- Department of Radiation Physics, The University of Texas MD Anderson Cancer Center, Houston, TX, 77030, USA.,The University of Texas MD Anderson Cancer Center UTHealth Graduate School of Biomedical Sciences, The University of Texas, Houston, TX, 77030, USA
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