Document Detail


Improvement of Varian a-Si EPID dosimetry measurements using a lead-shielded support-arm.
MedLine Citation:
PMID:  21925865     Owner:  NLM     Status:  Publisher    
Abstract/OtherAbstract:
Dosimetry measurements with Varian amorphous silicon electronic portal imaging devices (a-Si EPIDs) are affected by the backscattered radiation from the EPID support arm. In this study, the nonuniform backscatter from an E-type support arm was reduced by fixing a thick (12.2 × 10.5 × 0.5 cm(3)) piece of lead on top of the arm, and the remaining backscatter was modeled and included in an existing dose prediction algorithm. The applied backscatter kernel was the average of kernels on different regions of the EPID over the arm. The lead-shielded arm reduced the nonuniform backscatter component by about 50% for field sizes ranging from 3 × 3 to 30 × 30 cm(2) and the field symmetry improved for medium to large fields up to 3%. Gamma evaluation of the measured and modeled doses (2%, 2-mm criteria) showed that using the lead-shielded arm in the model increased the number of points with Gamma index <1 by 5.7% and decreased the mean Gamma by 0.201. Even using the lead alone (no modeling) could increase the number of points with Gamma index <1 by 4.7% and decrease the mean Gamma by 0.153. This is a simple and easy method to decrease the nonuniform arm backscatter and improve the accuracy of dosimetry measurements with the existing EPIDs used for clinical applications.
Authors:
Pejman Rowshanfarzad; Mahsheed Sabet; Daryl J O'Connor; Peter B Greer
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Publication Detail:
Type:  JOURNAL ARTICLE     Date:  2011-9-16
Journal Detail:
Title:  Medical dosimetry : official journal of the American Association of Medical Dosimetrists     Volume:  -     ISSN:  1873-4022     ISO Abbreviation:  -     Publication Date:  2011 Sep 
Date Detail:
Created Date:  2011-9-19     Completed Date:  -     Revised Date:  -    
Medline Journal Info:
Nlm Unique ID:  8908862     Medline TA:  Med Dosim     Country:  -    
Other Details:
Languages:  ENG     Pagination:  -     Citation Subset:  -    
Copyright Information:
Copyright © 2011 American Association of Medical Dosimetrists. Published by Elsevier Inc. All rights reserved.
Affiliation:
School of Mathematical and Physical Sciences, University of Newcastle, Newcastle, New South Wales, Australia.
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