Journal article
Brushed permanent magnet DC MLC motor operation in an external magnetic field
Medical physics (Lancaster), Vol.37(5), pp.2131-2134
04/23/2010
DOI: 10.1118/1.3392165
PMID: 20527546
Abstract
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.
Details
- Title: Subtitle
- Brushed permanent magnet DC MLC motor operation in an external magnetic field
- Creators
- J Yun - Department of Physics, University of Alberta, 11322-89 Avenue, Edmonton, Alberta T6G 2G7, Canadaand Department of Oncology, Medical Physics Division, University of Alberta, 11560 University Avenue, Edmonton, Alberta T6G 1Z2, CanadaJ St. Aubin - Department of Physics, University of Alberta, 11322-89 Avenue, Edmonton, Alberta T6G 2G7, Canadaand Department of Oncology, Medical Physics Division, University of Alberta, 11560 University Avenue, Edmonton, Alberta T6G 1Z2, CanadaS Rathee - Department of Medical Physics, Cross Cancer Institute, 11560 University Avenue, Edmonton,Alberta T6G 1Z2, Canada and Department of Oncology, Medical Physics Division, University of Alberta, 11560 University Avenue, Edmonton, Alberta T6G 1Z2, CanadaB G Fallone - Department of Physics, University of Alberta, 11322-89 Avenue, Edmonton, Alberta T6G 2G7, Canada; Department of Medical Physics, Cross Cancer Institute, 11560 University Avenue, Edmonton,Alberta T6G 1Z2, Canada; and Department of Oncology, Medical Physics Division, University of Alberta, 11560 University Avenue, Edmonton, Alberta T6G 1Z2, Canada
- Resource Type
- Journal article
- Publication Details
- Medical physics (Lancaster), Vol.37(5), pp.2131-2134
- Publisher
- American Association of Physicists in Medicine
- DOI
- 10.1118/1.3392165
- PMID
- 20527546
- ISSN
- 0094-2405
- eISSN
- 2473-4209
- Date published
- 04/23/2010
- Academic Unit
- Radiation Oncology
- Record Identifier
- 9984047866802771
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