Document Detail

Dosimetric effect of collimating jaws for small multileaf collimated fields.
MedLine Citation:
PMID:  15839348     Owner:  NLM     Status:  MEDLINE    
The dosimetric effects from the jaw positioned close to the small field (0.5 x 0.5, 1 x 1, and 2 x 2 cm2) side-edge generated by a single-focused multileaf collimator (MLC) were measured and studied. The measurement is important in intensity modulated radiotherapy (IMRT) because generally the jaw cannot perfectly cover all the leaf-ends in a segment of irregular field. This leads to additional dose contributed by (1) the end surface of the jaw, (2) the leaf-end, and (3) the inter- and intraleaf leakage/transmissions during the dosimetric measurement. Moreover, most of the conventional treatment planning systems ignore these effects in the dose calculation. In this study, measurements were made using a Varian 21 EX linear accelerator with 6 MV photon beam through a MLC containing 120 leaves. Percentage depth dose, beam profile, and output for small fields were measured by varying the jaw at different positions away from the leaf-ends in the field side-edge. Moving the jaw away from the leaf-ends increases the output and penumbra width for the small fields. Such increase is particularly significant when the field size is small (0.5 x 0.5 cm2) and the degree of increase changes quickly when the jaw-end is at about 1-2 cm from the leaf-end. It is suggested that measurements should be carried out in the IMRT commissioning to provide information to physicists in reviewing the treatment planning system's accuracy regarding leaf leakage/transmission and jaw effects.
James C L Chow; Melanie Seguin; Andrew Alexander
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Publication Detail:
Type:  Evaluation Studies; Journal Article    
Journal Detail:
Title:  Medical physics     Volume:  32     ISSN:  0094-2405     ISO Abbreviation:  Med Phys     Publication Date:  2005 Mar 
Date Detail:
Created Date:  2005-04-20     Completed Date:  2005-07-12     Revised Date:  -    
Medline Journal Info:
Nlm Unique ID:  0425746     Medline TA:  Med Phys     Country:  United States    
Other Details:
Languages:  eng     Pagination:  759-65     Citation Subset:  IM    
Medical Physics Department, Grand River Regional Cancer Center, Grand River Hospital, PO. Box 9056, 835 King Street West, Kitchener, Ontario N2G 1G3, Canada.
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MeSH Terms
Equipment Failure
Equipment Failure Analysis / methods*
Quality Assurance, Health Care / methods*
Radiation Protection / methods*
Radiometry / methods*
Radiotherapy Dosage
Radiotherapy Planning, Computer-Assisted / methods*
Radiotherapy, Conformal / instrumentation*,  methods*
Risk Assessment / methods*
Risk Factors
Scattering, Radiation

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

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