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Two‐dimensional measurement of photon beam attenuation by the treatment couch and immobilization devices using an electronic portal imaging device
Author(s) -
Vieira Sandra C.,
Kaatee Robert S. J. P.,
Dirkx Maarten L. P.,
Heijmen Ben J. M.
Publication year - 2003
Publication title -
medical physics
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.473
H-Index - 180
eISSN - 2473-4209
pISSN - 0094-2405
DOI - 10.1118/1.1620491
Subject(s) - attenuation , quality assurance , radiation treatment planning , dosimetry , medicine , medical physics , nuclear medicine , radiation therapy , image guided radiation therapy , radiology , optics , physics , external quality assessment , pathology
In our institution, an individualized dosimetric quality assurance protocol for intensity modulated radiotherapy (IMRT) is being implemented. This protocol includes dosimetric measurements with a fluoroscopic electronic portal imaging device (EPID) for all IMRT fields while the patient is being irradiated. For some of the first patients enrolled in this protocol, significant beam attenuation by (carbon fiber) components of the treatment couch was observed. To study this beam attenuation in two‐dimensional, EPID images were also acquired in absence of the patient, both with and without treatment couch and immobilization devices, as positioned during treatment. For treatments of head and neck cancer patients with a 6 MV photon beam, attenuation of up to 15% was detected. These findings led to the development of new tools and procedures for planning and treatment delivery to avoid underdosages in the tumor.