| Brushed permanent magnet DC MLC motor operation in an external magnetic field. | |
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MedLine Citation:
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PMID: 20527546 Owner: NLM Status: MEDLINE |
Abstract/OtherAbstract:
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PURPOSE: Linac-MR systems for real-time image-guided radiotherapy will utilize the multileaf collimators (MLCs) to perform conformal radiotherapy and tumor tracking. The MLCs would be exposed to the external fringe magnetic fields of the linac-MR hybrid systems. Therefore, an experimental investigation of the effect of an external magnetic field on the brushed permanent magnet DC motors used in some MLC systems was performed. METHODS: The changes in motor speed and current were measured for varying external magnetic field strengths up to 2000 G generated by an EEV electromagnet. These changes in motor characteristics were measured for three orientations of the motor in the external magnetic field, mimicking changes in motor orientations due to installation and/or collimator rotations. In addition, the functionality of the associated magnetic motor encoder was tested. The tested motors are used with the Varian 120 leaf Millennium MLC (Maxon Motor half leaf and full leaf motors) and the Varian 52 leaf MKII MLC (MicroMo Electronics leaf motor) including a carriage motor (MicroMo Electronics). RESULTS: In most cases, the magnetic encoder of the motors failed prior to any damage to the gearbox or the permanent magnet motor itself. This sets an upper limit of the external magnetic field strength on the motor function. The measured limits of the external magnetic fields were found to vary by the motor type. The leaf motor used with a Varian 52 leaf MKII MLC system tolerated up to 450 +/- 10 G. The carriage motor tolerated up to 2000 +/- 10 G field. The motors used with the Varian 120 leaf Millennium MLC system were found to tolerate a maximum of 600 +/- 10 G. CONCLUSIONS: The current Varian MLC system motors can be used for real-time image-guided radiotherapy coupled to a linac-MR system, provided the fringe magnetic fields at their locations are below the determined tolerance levels. With the fringe magnetic fields of linac-MR systems expected to be larger than the tolerance levels determined, some form of magnetic shielding would be required. |
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Authors:
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J Yun; J St Aubin; S Rathee; B G Fallone |
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Publication Detail:
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Type: Journal Article |
Journal Detail:
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Title: Medical physics Volume: 37 ISSN: 0094-2405 ISO Abbreviation: Med Phys Publication Date: 2010 May |
Date Detail:
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Created Date: 2010-06-09 Completed Date: 2010-06-28 Revised Date: - |
Medline Journal Info:
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Nlm Unique ID: 0425746 Medline TA: Med Phys Country: United States |
Other Details:
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Languages: eng Pagination: 2131-4 Citation Subset: IM |
Affiliation:
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Department of Physics, University of Alberta, 11322-89 Avenue, Edmonton, Alberta T6G 2G7, Canada. |
Export Citation:
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| MeSH Terms | |
Descriptor/Qualifier:
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Electric Conductivity Kinetics Magnetics* Radiotherapy, Computer-Assisted / methods* |
From MEDLINE®/PubMed®, a database of the U.S. National Library of Medicine
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