| Magnetic-field-induced dose effects in MR-guided radiotherapy systems: dependence on the magnetic field strength. | |
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MedLine Citation:
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PMID: 18263948 Owner: NLM Status: MEDLINE |
Abstract/OtherAbstract:
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Several institutes are currently working on the development of a radiotherapy treatment system with online MR imaging (MRI) modality. The main difference between their designs is the magnetic field strength of the MRI system. While we have chosen a 1.5 Tesla (T) magnetic field strength, the Cross Cancer Institute in Edmonton will be using a 0.2 T MRI scanner and the company Viewray aims to use 0.3 T. The magnetic field strength will affect the severity of magnetic field dose effects, such as the electron return effect (ERE): considerable dose increase at tissue air boundaries due to returning electrons. This paper has investigated how the ERE dose increase depends on the magnetic field strength. Therefore, four situations where the ERE occurs have been simulated: ERE at the distal side of the beam, the lateral ERE, ERE in cylindrical air cavities and ERE in the lungs. The magnetic field comparison values were 0.2, 0.75, 1.5 and 3 T. Results show that, in general, magnetic field dose effects are reduced at lower magnetic field strengths. At the distal side, the ERE dose increase is largest for B = 0.75 T and depends on the irradiation field size for B = 0.2 T. The lateral ERE is strongest for B = 3 T but shows no effect for B = 0.2 T. Around cylindrical air cavities, dose inhomogeneities disappear if the radius of the cavity becomes small relative to the in-air radius of the secondary electron trajectories. At larger cavities (r > 1 cm), dose inhomogeneities exist for all magnetic field strengths. In water-lung-water phantoms, the ERE dose increase takes place at the water-lung transition and the dose decreases at the lung-water transition, but these effects are minimal for B = 0.2 T. These results will contribute to evaluating the trade-off between magnetic field dose effects and image quality of MR-guided radiotherapy systems. |
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Authors:
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A J E Raaijmakers; B W Raaymakers; J J W Lagendijk |
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Publication Detail:
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Type: Journal Article; Research Support, Non-U.S. Gov't Date: 2008-01-18 |
Journal Detail:
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Title: Physics in medicine and biology Volume: 53 ISSN: 0031-9155 ISO Abbreviation: Phys Med Biol Publication Date: 2008 Feb |
Date Detail:
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Created Date: 2008-02-11 Completed Date: 2008-05-07 Revised Date: - |
Medline Journal Info:
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Nlm Unique ID: 0401220 Medline TA: Phys Med Biol Country: England |
Other Details:
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Languages: eng Pagination: 909-23 Citation Subset: IM |
Affiliation:
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Department of Radiotherapy, University Medical Center Utrecht, Heidelberglaan 100, Utrecht, The Netherlands. A.J.E.Raaymakers@umcutrecht.nl |
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| MeSH Terms | |
Descriptor/Qualifier:
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Electrons Lung / cytology Magnetic Resonance Imaging* Magnetics* Monte Carlo Method Radiation Dosage* Radiotherapy, Computer-Assisted / methods* |
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