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Begg J, Jelen U, Moutrie Z, Oliver C, Holloway L, Brown R. ACPSEM position paper: dosimetry for magnetic resonance imaging linear accelerators. Phys Eng Sci Med 2023; 46:1-17. [PMID: 36806156 PMCID: PMC10030536 DOI: 10.1007/s13246-023-01223-w] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Accepted: 01/19/2023] [Indexed: 02/23/2023]
Abstract
Consistency and clear guidelines on dosimetry are essential for accurate and precise dosimetry, to ensure the best patient outcomes and to allow direct dose comparison across different centres. Magnetic Resonance Imaging Linac (MRI-linac) systems have recently been introduced to Australasian clinics. This report provides recommendations on reference dosimetry measurements for MRI-linacs on behalf of the Australiasian College of Physical Scientists and Engineers in Medicine (ACPSEM) MRI-linac working group. There are two configurations considered for MRI-linacs, perpendicular and parallel, referring to the relative direction of the magnetic field and radiation beam, with different impacts on dose deposition in a medium. These recommendations focus on ion chambers which are most commonly used in the clinic for reference dosimetry. Water phantoms must be MR safe or conditional and practical limitations on phantom set-up must be considered. Solid phantoms are not advised for reference dosimetry. For reference dosimetry, IAEA TRS-398 recommendations cannot be followed completely due to physical differences between conventional linac and MRI-linac systems. Manufacturers' advice on reference conditions should be followed. Beam quality specification of TPR20,10 is recommended. The configuration of the central axis of the ion chamber relative to the magnetic field and radiation beam impacts the chamber response and must be considered carefully. Recommended corrections to delivered dose are [Formula: see text], a correction for beam quality and [Formula: see text], for the impact of the magnetic field on dosimeter response in the magnetic field. Literature based values for [Formula: see text] are given. It is important to note that this is a developing field and these recommendations should be used together with a review of current literature.
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Affiliation(s)
- Jarrad Begg
- Department of Medical Physics, Liverpool and Macarthur Cancer Therapy Centre, Liverpool, NSW, 2170, Australia.
- Ingham Institute for Applied Medical Research, Liverpool, NSW, 2170, Australia.
- South Western Sydney Clinical School, University of New South Wales, Liverpool, NSW, 2170, Australia.
| | - Urszula Jelen
- St Vincents Clinic, GenesisCare, Darlinghurst, NSW, 2010, Australia
| | - Zoe Moutrie
- Department of Medical Physics, Liverpool and Macarthur Cancer Therapy Centre, Liverpool, NSW, 2170, Australia
| | - Chris Oliver
- Primary Standards Dosimetry Laboratory, Australian Radiation Protection and Nuclear Safety Agency, Yallambie, VIC, 3085, Australia
| | - Lois Holloway
- Department of Medical Physics, Liverpool and Macarthur Cancer Therapy Centre, Liverpool, NSW, 2170, Australia
- Ingham Institute for Applied Medical Research, Liverpool, NSW, 2170, Australia
- South Western Sydney Clinical School, University of New South Wales, Liverpool, NSW, 2170, Australia
- Centre for Medical Radiation Physics, University of Wollongong, Wollongong, NSW, 2522, Australia
- Institute of Medical Physics, University of Sydney, Camperdown, NSW, 2505, Australia
| | - Rhonda Brown
- Australian Clinical Dosimetry Service, Australian Radiation Protection and Nuclear Safety Agency, Yallambie, VIC, 3085, Australia
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Reis CQM, Robar JL. Evaluation of the feasibility of cardiac gating for SBRT of ventricular tachycardia based on real-time ECG signal acquisition. J Appl Clin Med Phys 2022; 24:e13814. [PMID: 36286619 PMCID: PMC9924123 DOI: 10.1002/acm2.13814] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/02/2022] [Revised: 09/10/2022] [Accepted: 09/30/2022] [Indexed: 11/08/2022] Open
Abstract
PURPOSE To investigate the feasibility of cardiac synchronized gating in stereotactic body radiation therapy (SBRT) of ventricular tachycardia (VT) using a real-time electrocardiogram (ECG) signal acquisition. METHODS AND MATERIALS Stability of beam characteristics during simulated ECG gating was examined by developing a microcontroller interface to a Varian Clinac iX linear accelerator allowing gating at frequencies and duty cycles relevant to cardiac rhythm. Delivery accuracy was evaluated by measuring dose linearity with an ionization chamber, and flatness and symmetry with a two-dimensional detector array, for different gating windows within typical human cardiac cycle periods. To establish a practical method of gating based on actual ECG signals, an AD8232 Heart Monitor board was used to acquire the ECG signal and synchronize the beam delivery. Real-time cardiac gated delivery measurements were performed for a single 10 × 10 cm2 field and for a VT-SBRT plan using intensity-modulated radiation therapy (IMRT). RESULTS AND DISCUSSION Dose per monitor unit (MU) values were found to be linear within most gating windows investigated with maximum differences relative to non-gated delivery of <2% for gating windows ≥200 ms and for >10 MUs. Beam profiles for both gated and non-gated modes were also found to agree with maximum differences of 0.5% relative to central axis dose for all sets of beam-on/beam-off combinations. Comparison of dose distributions for intensity-modulated SBRT plans between non-gating and cardiac gating modes provided a gamma passing rate of 97.2% for a 2% 2 mm tolerance. CONCLUSIONS Beam output is stable with respect to linearity, flatness, and symmetry for gating windows within cardiac cycle periods. Agreement between dose distributions for VT-SBRT using IMRT in non-gated and cardiac cycle gated delivery modes shows that the proposed methodology is feasible. Technically, gating for delivery of SBRT for VT is possible with regard to beam stability.
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Affiliation(s)
- Cristiano Q. M. Reis
- Department of Radiation OncologyDalhousie UniversityHalifaxNova ScotiaCanada,Department of Medical PhysicsNova Scotia HealthHalifaxNova ScotiaCanada,Department of Physics and Atmospheric ScienceDalhousie UniversityHalifaxNova ScotiaCanada
| | - James L. Robar
- Department of Radiation OncologyDalhousie UniversityHalifaxNova ScotiaCanada,Department of Medical PhysicsNova Scotia HealthHalifaxNova ScotiaCanada,Department of Physics and Atmospheric ScienceDalhousie UniversityHalifaxNova ScotiaCanada
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Lee YS, Kim S, Kim GJ, Lee JH, Kim IS, Kim JI, Shin KY, Seol Y, Oh T, An NY, Lee J, Hwang J, Oh Y, Kang YN. Medical X-band linear accelerator for high-precision radiotherapy. Med Phys 2021; 48:5327-5342. [PMID: 34224166 DOI: 10.1002/mp.15077] [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: 03/29/2020] [Revised: 05/27/2021] [Accepted: 06/14/2021] [Indexed: 11/07/2022] Open
Abstract
PURPOSE Recently, high-precision radiotherapy systems have been developed by integrating computerized tomography or magnetic resonance imaging to enhance the precision of radiotherapy. For integration with additional imaging systems in a limited space, miniaturization and weight reduction of the linear accelerator (linac) system have become important. The aim of this work is to develop a compact medical linac based on 9.3 GHz X-band RF technology instead of the S-band RF technology typically used in the radiotherapy field. METHODS The accelerating tube was designed by 3D finite-difference time-domain and particle-in-cell simulations because the frequency variation resulting from the structural parameters and processing errors is relatively sensitive to the operating performance of the X-band linac. Through the 3D simulation of the electric field distribution and beam dynamics process, we designed an accelerating tube to efficiently accelerate the electron beam and used a magnetron as the RF source to miniaturize the entire linac. In addition, a side-coupled structure was adopted to design a compact linac to reduce the RF power loss. To verify the performance of the linac, we developed a beam diagnostic system to analyze the electron beam characteristics and a quality assurance (QA) experimental environment including 3D lateral water phantoms to analyze the primary performance parameters (energy, dose rate, flatness, symmetry, and penumbra) The QA process was based on the standard protocols AAPM TG-51, 106, 142 and IAEA TRS-398. RESULTS The X-band linac has high shunt impedance and electric field strength. Therefore, even though the length of the accelerating tube is 37 cm, the linac could accelerate an electron beam to more than 6 MeV and produce a beam current of more than 90 mA. The transmission ratio is measured to be approximately 30% ~ 40% when the electron gun operates in the constant emission region. The percent depth dose ratio at the measured depths of 10 and 20 cm was approximately 0.572, so we verified that the photon beam energy was matched to approximately 6 MV. The maximum dose rate was measured as 820 cGy/min when the source-to-skin distance was 80 cm. The symmetry was smaller than the QA standard and the flatness had a higher than standard value due to the flattening filter-free beam characteristics. In the case of the penumbra, it was not sufficiently steep compared to commercial equipment, but it could be compensated by improving additional devices such as multileaf collimator and jaw. CONCLUSIONS A 9.3 GHz X-band medical linac was developed for high-precision radiotherapy. Since a more precise design and machining process are required for X-band RF technology, this linac was developed by performing a 3D simulation and ultraprecision machining. The X-band linac has a short length and a compact volume, but it can generate a validated therapeutic beam. Therefore, it has more flexibility to be coupled with imaging systems such as CT or MRI and can reduce the bore size of the gantry. In addition, the weight reduction can improve the mechanical stiffness of the unit and reduce the mechanical load.
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Affiliation(s)
- Yong-Seok Lee
- Electro-Medical Device Research Center, Korea Electrotechnology Research Institute, Ansan, Republic of Korea.,PLS-II Accelerator Division, Pohang Accelerator Laboratory, Pohang, Republic of Korea
| | - Sanghoon Kim
- Electro-Medical Device Research Center, Korea Electrotechnology Research Institute, Ansan, Republic of Korea
| | - Geun-Ju Kim
- Electro-Medical Device Research Center, Korea Electrotechnology Research Institute, Ansan, Republic of Korea
| | - Jeong-Hun Lee
- Electro-Medical Device Research Center, Korea Electrotechnology Research Institute, Ansan, Republic of Korea
| | - Insoo S Kim
- Electro-Medical Device Research Center, Korea Electrotechnology Research Institute, Ansan, Republic of Korea
| | - Jung-Il Kim
- Electro-Medical Device Research Center, Korea Electrotechnology Research Institute, Ansan, Republic of Korea
| | - Ki Young Shin
- Russia Science Seoul Center, Korea Electrotechnology Research Institute, Ansan, Republic of Korea
| | - Yunji Seol
- Department of Biomedicine & Health Sciences, The Catholic University of Korea, Seoul, Republic of Korea.,Advanced Institute for Radiation Fusion Medical Technology, College of Medicine, The Catholic University of Korea, Seoul, Republic of Korea
| | - Taegeon Oh
- Department of Biomedicine & Health Sciences, The Catholic University of Korea, Seoul, Republic of Korea.,Advanced Institute for Radiation Fusion Medical Technology, College of Medicine, The Catholic University of Korea, Seoul, Republic of Korea
| | - Na-Young An
- Department of Biomedicine & Health Sciences, The Catholic University of Korea, Seoul, Republic of Korea.,Advanced Institute for Radiation Fusion Medical Technology, College of Medicine, The Catholic University of Korea, Seoul, Republic of Korea
| | - Jaehyeon Lee
- Department of Biomedicine & Health Sciences, The Catholic University of Korea, Seoul, Republic of Korea.,Advanced Institute for Radiation Fusion Medical Technology, College of Medicine, The Catholic University of Korea, Seoul, Republic of Korea
| | - Jinho Hwang
- Department of Radiation Oncology, Incheon St. Mary's Hospital, College of Medicine, The Catholic University of Korea, Incheon, Republic of Korea
| | - Youngah Oh
- Advanced Institute for Radiation Fusion Medical Technology, College of Medicine, The Catholic University of Korea, Seoul, Republic of Korea
| | - Young-Nam Kang
- Advanced Institute for Radiation Fusion Medical Technology, College of Medicine, The Catholic University of Korea, Seoul, Republic of Korea.,Department of Radiation Oncology, Seoul St. Mary's Hospital, College of Medicine, The Catholic University of Korea, Seoul, Republic of Korea
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Jelen U, Dong B, Begg J, Roberts N, Whelan B, Keall P, Liney G. Dosimetric Optimization and Commissioning of a High Field Inline MRI-Linac. Front Oncol 2020; 10:136. [PMID: 32117776 PMCID: PMC7033562 DOI: 10.3389/fonc.2020.00136] [Citation(s) in RCA: 7] [Impact Index Per Article: 1.8] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/03/2019] [Accepted: 01/27/2020] [Indexed: 11/17/2022] Open
Abstract
Purpose: Unique characteristics of MRI-linac systems and mutual interactions between their components pose specific challenges for their commissioning and quality assurance. The Australian MRI-linac is a prototype system which explores the inline orientation, with radiation beam parallel to the main magnetic field. The aim of this work was to commission the radiation-related aspects of this system for its application in clinical treatments. Methods: Physical alignment of the radiation beam to the magnetic field was fine-tuned and magnetic shielding of the radiation head was designed to achieve optimal beam characteristics. These steps were guided by investigative measurements of the beam properties. Subsequently, machine performance was benchmarked against the requirements of the IEC60976/77 standards. Finally, the geometric and dosimetric data was acquired, following the AAPM Task Group 106 recommendations, to characterize the beam for modeling in the treatment planning system and with Monte Carlo simulations. The magnetic field effects on the dose deposition and on the detector response have been taken into account and issues specific to the inline design have been highlighted. Results: Alignment of the radiation beam axis and the imaging isocentre within 2 mm tolerance was obtained. The system was commissioned at two source-to-isocentre distances (SIDs): 2.4 and 1.8 m. Reproducibility and proportionality of the dose monitoring system met IEC criteria at the larger SID but slightly exceeded it at the shorter SID. Profile symmetry remained under 103% for the fields up to ~34 × 34 and 21 × 21 cm2 at the larger and shorter SID, respectively. No penumbra asymmetry, characteristic for transverse systems, was observed. The electron focusing effect, which results in high entrance doses on central axis, was quantified and methods to minimize it have been investigated. Conclusion: Methods were developed and employed to investigate and quantify the dosimetric properties of an inline MRI-Linac system. The Australian MRI-linac system has been fine-tuned in terms of beam properties and commissioned, constituting a key step toward the application of inline MRI-linacs for patient treatments.
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Affiliation(s)
- Urszula Jelen
- Department of Medical Physics, Ingham Institute for Applied Medical Research, Liverpool, NSW, Australia
| | - Bin Dong
- Department of Medical Physics, Ingham Institute for Applied Medical Research, Liverpool, NSW, Australia
| | - Jarrad Begg
- Department of Medical Physics, Ingham Institute for Applied Medical Research, Liverpool, NSW, Australia.,Liverpool Cancer Therapy Centre, Radiation Physics, Liverpool, NSW, Australia.,School of Medicine, University of New South Wales, Sydney, NSW, Australia
| | - Natalia Roberts
- Department of Medical Physics, Ingham Institute for Applied Medical Research, Liverpool, NSW, Australia.,Centre for Medical Radiation Physics, University of Wollongong, Wollongong, NSW, Australia
| | - Brendan Whelan
- Sydney Medical School, ACRF Image X Institute, University of Sydney, Sydney, NSW, Australia
| | - Paul Keall
- Department of Medical Physics, Ingham Institute for Applied Medical Research, Liverpool, NSW, Australia.,Sydney Medical School, ACRF Image X Institute, University of Sydney, Sydney, NSW, Australia
| | - Gary Liney
- Department of Medical Physics, Ingham Institute for Applied Medical Research, Liverpool, NSW, Australia.,Liverpool Cancer Therapy Centre, Radiation Physics, Liverpool, NSW, Australia.,School of Medicine, University of New South Wales, Sydney, NSW, Australia.,Centre for Medical Radiation Physics, University of Wollongong, Wollongong, NSW, Australia
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Begg J, Alnaghy SJ, Causer T, Alharthi T, George A, Glaubes L, Dong B, Goozee G, Keall P, Jelen U, Liney G, Holloway L. Technical Note: Experimental characterization of the dose deposition in parallel MRI‐linacs at various magnetic field strengths. Med Phys 2019; 46:5152-5158. [DOI: 10.1002/mp.13767] [Citation(s) in RCA: 6] [Impact Index Per Article: 1.2] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/29/2019] [Revised: 08/05/2019] [Accepted: 08/06/2019] [Indexed: 11/05/2022] Open
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
| | - Sarah J. Alnaghy
- Ingham Institute for Applied Medical Research Liverpool NSW 2170 Australia
- Centre for Medical Radiation Physics University of Wollongong Wollongong NSW 2522 Australia
| | - Trent Causer
- Ingham Institute for Applied Medical Research Liverpool NSW 2170 Australia
- Centre for Medical Radiation Physics University of Wollongong Wollongong NSW 2522 Australia
| | - Thahabah Alharthi
- Ingham Institute for Applied Medical Research Liverpool NSW 2170 Australia
- Sydney Medical School University of Sydney Camperdown NSW 2505 Australia
| | - Armia George
- Department of Medical Physics, Liverpool and Macarthur Cancer Therapy Centre Liverpool NSW 2170 Australia
- Ingham Institute for Applied Medical Research Liverpool NSW 2170 Australia
| | - Laura Glaubes
- Sydney Medical School University of Sydney Camperdown NSW 2505 Australia
| | - Bin Dong
- Ingham Institute for Applied Medical Research Liverpool NSW 2170 Australia
- Centre for Medical Radiation Physics University of Wollongong Wollongong NSW 2522 Australia
| | - Gary Goozee
- Department of Medical Physics, Liverpool and Macarthur Cancer Therapy Centre Liverpool NSW 2170 Australia
- Ingham Institute for Applied Medical Research Liverpool NSW 2170 Australia
| | - Paul Keall
- Ingham Institute for Applied Medical Research Liverpool NSW 2170 Australia
- ACRF Image X Institute , Sydney Medical School, University of Sydney Liverpool NSW2170 Australia
| | - Urszula Jelen
- Ingham Institute for Applied Medical Research Liverpool NSW 2170 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
- Centre for Medical Radiation Physics University of Wollongong Wollongong NSW 2522 Australia
- Sydney Medical School University of Sydney Camperdown NSW 2505 Australia
| | - Lois Holloway
- Department of Medical Physics, Liverpool and Macarthur Cancer Therapy Centre Liverpool NSW 2170 Australia
- Ingham Institute for Applied Medical Research Liverpool NSW 2170 Australia
- South Western Sydney Clinical School University of New South Wales Liverpool NSW 2170 Australia
- Centre for Medical Radiation Physics University of Wollongong Wollongong NSW 2522 Australia
- Institute of Medical Physics University of Sydney Camperdown NSW 2505 Australia
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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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Pollard JM, Wen Z, Sadagopan R, Wang J, Ibbott GS. The future of image-guided radiotherapy will be MR guided. Br J Radiol 2017; 90:20160667. [PMID: 28256898 DOI: 10.1259/bjr.20160667] [Citation(s) in RCA: 130] [Impact Index Per Article: 18.6] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/14/2022] Open
Abstract
Advances in image-guided radiotherapy (RT) have allowed for dose escalation and more precise radiation treatment delivery. Each decade brings new imaging technologies to help improve RT patient setup. Currently, the most frequently used method of three-dimensional pre-treatment image verification is performed with cone beam CT. However, more recent developments have provided RT with the ability to have on-board MRI coupled to the teleradiotherapy unit. This latest tool for treating cancer is known as MR-guided RT. Several varieties of these units have been designed and installed in centres across the globe. Their prevalence, history, advantages and disadvantages are discussed in this review article. In preparation for the next generation of image-guided RT, this review also covers where MR-guided RT might be heading in the near future.
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Affiliation(s)
| | - Zhifei Wen
- UT MD Anderson Cancer Center, Houston, TX, USA
| | | | - Jihong Wang
- UT MD Anderson Cancer Center, Houston, TX, USA
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