The use of an electronic portal imaging device for exit dosimetry and quality control measurements.

2.50
Hdl Handle:
http://hdl.handle.net/10541/99009
Title:
The use of an electronic portal imaging device for exit dosimetry and quality control measurements.
Authors:
Kirby, Mike C; Williams, Peter C
Abstract:
PURPOSE: To determine ways in which electronic portal imaging devices (EPIDs) could be used to (a) measure exit doses for external beam radiotherapy and (b) perform quality control checks on linear accelerators. METHODS AND MATERIALS: When imaging, our fluoroscopic EPID adjusts the gain, offset, and frame acquisition time of the charge coupled device (CCD) camera automatically, to allow for the range of photon transmissions through the patient, and to optimize the signal-to-noise ratio. However, our EPID can be programmed to act as an integrating dosemeter. EPID dosemeter measurements were made for 20 MV photons, for different field sizes and thicknesses of unit density phantom material placed at varying exit surface to detector distances. These were compared with simultaneous Silicon diode exit dose measurements. Our exit dosimetry technique was verified using an anthropomorphic type phantom, and some initial measurements have been made for patients treated with irregularly shaped 20 MV x-ray fields. In this dosimetry mode, our EPID was also used to measure certain quality control parameters, x-ray field flatness, and the verification of segmented intensity modulated field prescriptions. RESULTS: Configured for dosimetry, our EPID exhibited a highly linear response, capable of resolving individual monitor units. Exit doses could be measured to within about 3% of that measured using Silicon diodes. Field flatness was determined to within 1.5% of Farmer dosemeter measurements. Segmented intensity modulated fields can be easily verified. CONCLUSIONS: Our EPID has the versatility to assess a range of parameters pertinent to the delivery of high quality, high precision radiotherapy. When configured appropriately, it can measure exit doses in vivo, with reasonable accuracy, perform certain quick quality control checks, and analyze segmented intensity modulated treatment fields.
Affiliation:
North Western Medical Physics Department, Christie Hospital, Manchester, UK.
Citation:
The use of an electronic portal imaging device for exit dosimetry and quality control measurements. 1995, 31 (3):593-603 Int. J. Radiat. Oncol. Biol. Phys.
Journal:
International Journal of Radiation Oncology, Biology, Physics
Issue Date:
1-Feb-1995
URI:
http://hdl.handle.net/10541/99009
DOI:
10.1016/0360-3016(94)00388-2
PubMed ID:
7852125
Type:
Article
Language:
en
ISSN:
0360-3016
Appears in Collections:
All Christie Publications

Full metadata record

DC FieldValue Language
dc.contributor.authorKirby, Mike Cen
dc.contributor.authorWilliams, Peter Cen
dc.date.accessioned2010-05-17T15:58:42Z-
dc.date.available2010-05-17T15:58:42Z-
dc.date.issued1995-02-01-
dc.identifier.citationThe use of an electronic portal imaging device for exit dosimetry and quality control measurements. 1995, 31 (3):593-603 Int. J. Radiat. Oncol. Biol. Phys.en
dc.identifier.issn0360-3016-
dc.identifier.pmid7852125-
dc.identifier.doi10.1016/0360-3016(94)00388-2-
dc.identifier.urihttp://hdl.handle.net/10541/99009-
dc.description.abstractPURPOSE: To determine ways in which electronic portal imaging devices (EPIDs) could be used to (a) measure exit doses for external beam radiotherapy and (b) perform quality control checks on linear accelerators. METHODS AND MATERIALS: When imaging, our fluoroscopic EPID adjusts the gain, offset, and frame acquisition time of the charge coupled device (CCD) camera automatically, to allow for the range of photon transmissions through the patient, and to optimize the signal-to-noise ratio. However, our EPID can be programmed to act as an integrating dosemeter. EPID dosemeter measurements were made for 20 MV photons, for different field sizes and thicknesses of unit density phantom material placed at varying exit surface to detector distances. These were compared with simultaneous Silicon diode exit dose measurements. Our exit dosimetry technique was verified using an anthropomorphic type phantom, and some initial measurements have been made for patients treated with irregularly shaped 20 MV x-ray fields. In this dosimetry mode, our EPID was also used to measure certain quality control parameters, x-ray field flatness, and the verification of segmented intensity modulated field prescriptions. RESULTS: Configured for dosimetry, our EPID exhibited a highly linear response, capable of resolving individual monitor units. Exit doses could be measured to within about 3% of that measured using Silicon diodes. Field flatness was determined to within 1.5% of Farmer dosemeter measurements. Segmented intensity modulated fields can be easily verified. CONCLUSIONS: Our EPID has the versatility to assess a range of parameters pertinent to the delivery of high quality, high precision radiotherapy. When configured appropriately, it can measure exit doses in vivo, with reasonable accuracy, perform certain quick quality control checks, and analyze segmented intensity modulated treatment fields.en
dc.language.isoenen
dc.subject.meshHumans-
dc.subject.meshQuality Control-
dc.subject.meshRadiotherapy-
dc.subject.meshRadiotherapy Dosage-
dc.subject.meshSignal Processing, Computer-Assisted-
dc.titleThe use of an electronic portal imaging device for exit dosimetry and quality control measurements.en
dc.typeArticleen
dc.contributor.departmentNorth Western Medical Physics Department, Christie Hospital, Manchester, UK.en
dc.identifier.journalInternational Journal of Radiation Oncology, Biology, Physicsen
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