Document Detail

Monitor unit calculations for wedged asymmetric photon beams.
MedLine Citation:
PMID:  12118598     Owner:  NLM     Status:  MEDLINE    
Algorithms for calculating monitor units (MUs) in wedged asymmetric high-energy photon beams as implemented in treatment planning systems have their limitations. Therefore an independent method for MU calculation is necessary. The aim of this study was to develop an empirical method to determine MUs for points at the centre of wedged fields, asymmetric in two directions. The method is based on the determination of an off-axis factor (OAF) that corrects for the difference in dose between wedged asymmetric and wedged symmetric beams with the same field size. Measurements were performed in a water phantom irradiated with 6 and 18 MV photon beams produced by Elekta accelerators, which are fitted with an internal motorized wedge that has a complex shape. The OAF perpendicular to the wedge direction changed significantly with depth for the 18 MV beam. Dose values measured for a set of 18 test cases were compared with those calculated with our method. The maximum difference found was 6.5% and in 15 cases this figure was smaller than 2.0%. The analytical method of Khan and the empirical method of Georg were also tested and showed errors up to 12.8%. It can be concluded that our simple formalism is able to calculate MUs in wedged asymmetric fields with an acceptable accuracy in most clinical situations.
Bob Smulders; Iaïn A D Bruinvis; Ben J Mijnheer
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Publication Detail:
Type:  Journal Article    
Journal Detail:
Title:  Physics in medicine and biology     Volume:  47     ISSN:  0031-9155     ISO Abbreviation:  Phys Med Biol     Publication Date:  2002 Jun 
Date Detail:
Created Date:  2002-07-16     Completed Date:  2003-01-07     Revised Date:  -    
Medline Journal Info:
Nlm Unique ID:  0401220     Medline TA:  Phys Med Biol     Country:  England    
Other Details:
Languages:  eng     Pagination:  2013-30     Citation Subset:  IM    
Department of Radiotherapy, The Netherlands Cancer Institute/Antoni van Leeuwenhoek Hospital, Amsterdam.
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MeSH Terms
Models, Theoretical
Phantoms, Imaging
Radiometry / methods*
Radiotherapy Planning, Computer-Assisted / methods*
Reproducibility of Results
Time Factors

From MEDLINE®/PubMed®, a database of the U.S. National Library of Medicine

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