Analysis of the measurement precision of an amorphous silicon EPID used for MLC leaf position quality control and the long-term calibration stability of an optically controlled MLC.

2.50
Hdl Handle:
http://hdl.handle.net/10541/66853
Title:
Analysis of the measurement precision of an amorphous silicon EPID used for MLC leaf position quality control and the long-term calibration stability of an optically controlled MLC.
Authors:
Budgell, Geoff J; Clarke, Mathew F
Abstract:
Electronic portal imaging devices (EPIDs) have been shown to be suitable for multileaf collimator (MLC) leaf positioning quality control (QC). In our centre, a continuous dataset is available of 2 years of film measurements followed by 3 years of EPID measurements on five MLC-equipped linear accelerators of identical head design. The aim of this work was to analyse this unique dataset in order to determine the relative precision of film and EPID for MLC leaf positioning measurements and to determine the long-term stability of the MLC calibration. The QC dataset was examined and periods without MLC adjustments that contained at least four successive collimator position measurements (a minimum of 6 months) were identified. By calculating the standard deviations (SD) of these results, the reproducibility of the measurements can be determined. Comparison of the film and EPID results enables their relative measurement precision to be assessed; on average film gave an SD of 0.52 mm compared to 0.13 mm for EPIDs. The MLC and conventional collimator results were compared to assess MLC calibration stability; on average, for EPID measurements, the MLC gave an SD of 0.12 mm compared to 0.14 mm for a conventional collimator. The long-term relative individual leaf positions were compared and found to vary between 0.07 and 0.15 mm implying that they are stable over long time periods. These results suggest that the calibration of an optically controlled MLC is inherently very stable between disturbances to the optical system which normally occur on service days.
Affiliation:
North Western Medical Physics, Christie Hospital NHS Foundation Trust, Withington, Manchester, M20 4BX, UK.
Citation:
Analysis of the measurement precision of an amorphous silicon EPID used for MLC leaf position quality control and the long-term calibration stability of an optically controlled MLC. 2008, 53 (15):N297-306 Phys Med Biol
Journal:
Physics in Medicine and Biology
Issue Date:
7-Aug-2008
URI:
http://hdl.handle.net/10541/66853
DOI:
10.1088/0031-9155/53/15/N01
PubMed ID:
18635894
Type:
Article
Language:
en
ISSN:
0031-9155
Appears in Collections:
All Christie Publications ; Christie Medical Physics and Engineering Research

Full metadata record

DC FieldValue Language
dc.contributor.authorBudgell, Geoff J-
dc.contributor.authorClarke, Mathew F-
dc.date.accessioned2009-05-01T10:26:13Z-
dc.date.available2009-05-01T10:26:13Z-
dc.date.issued2008-08-07-
dc.identifier.citationAnalysis of the measurement precision of an amorphous silicon EPID used for MLC leaf position quality control and the long-term calibration stability of an optically controlled MLC. 2008, 53 (15):N297-306 Phys Med Biolen
dc.identifier.issn0031-9155-
dc.identifier.pmid18635894-
dc.identifier.doi10.1088/0031-9155/53/15/N01-
dc.identifier.urihttp://hdl.handle.net/10541/66853-
dc.description.abstractElectronic portal imaging devices (EPIDs) have been shown to be suitable for multileaf collimator (MLC) leaf positioning quality control (QC). In our centre, a continuous dataset is available of 2 years of film measurements followed by 3 years of EPID measurements on five MLC-equipped linear accelerators of identical head design. The aim of this work was to analyse this unique dataset in order to determine the relative precision of film and EPID for MLC leaf positioning measurements and to determine the long-term stability of the MLC calibration. The QC dataset was examined and periods without MLC adjustments that contained at least four successive collimator position measurements (a minimum of 6 months) were identified. By calculating the standard deviations (SD) of these results, the reproducibility of the measurements can be determined. Comparison of the film and EPID results enables their relative measurement precision to be assessed; on average film gave an SD of 0.52 mm compared to 0.13 mm for EPIDs. The MLC and conventional collimator results were compared to assess MLC calibration stability; on average, for EPID measurements, the MLC gave an SD of 0.12 mm compared to 0.14 mm for a conventional collimator. The long-term relative individual leaf positions were compared and found to vary between 0.07 and 0.15 mm implying that they are stable over long time periods. These results suggest that the calibration of an optically controlled MLC is inherently very stable between disturbances to the optical system which normally occur on service days.en
dc.language.isoenen
dc.subjectElectronic Portal Imaging Devicesen
dc.subjectMultileaf Collimatoren
dc.subject.meshCalibration-
dc.subject.meshOptics and Photonics-
dc.subject.meshQuality Control-
dc.subject.meshRadiotherapy-
dc.subject.meshSensitivity and Specificity-
dc.subject.meshSilicon-
dc.subject.meshTime Factors-
dc.titleAnalysis of the measurement precision of an amorphous silicon EPID used for MLC leaf position quality control and the long-term calibration stability of an optically controlled MLC.en
dc.typeArticleen
dc.contributor.departmentNorth Western Medical Physics, Christie Hospital NHS Foundation Trust, Withington, Manchester, M20 4BX, UK.en
dc.identifier.journalPhysics in Medicine and Biologyen
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