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

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    Authors
    Kirby, Mike C
    Williams, Peter C
    Affiliation
    North Western Medical Physics Department, Christie Hospital, Manchester, UK.
    Issue Date
    1995-02-01
    
    Metadata
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    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.
    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
    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
    ae974a485f413a2113503eed53cd6c53
    10.1016/0360-3016(94)00388-2
    Scopus Count
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