Document Detail

A macropencil beam model: clinical implementation for conformal and intensity modulated radiation therapy.
MedLine Citation:
PMID:  10232815     Owner:  NLM     Status:  MEDLINE    
The increasing use of irregularly shaped, off-centre fields in advanced treatment techniques, particularly intensity modulated radiation therapy, has strained the limits of conventional, broad-beam dose calculation algorithms. More recent models, such as kernel-based pencil beams and Monte Carlo methods, are accurate but suffer from the time needed for calculations and from the lack of clearly established methods for determining the parameters needed to match calculations with the particular dosimetric characteristics of an individual machine. This paper presents the implementation of a model that uses an extended source model to calculate the variation of fluence at the patient surface for any arbitrarily shaped field. It uses a macropencil beam model to calculate phantom scatter. Both head scatter and phantom scatter models use exponential functions fit to a series of measurements to determine the model's parameters. The means by which the model can be implemented in a clinical setting using standard dosimetric equipment is presented. Results for two separate machines and three energies are presented. Comparisons with measurements for a set of regular and irregular fields demonstrate the accuracy of the model for conventional, conformal and intensity modulated treatments. For rectangular and irregular fields at depths up to 20 cm, the accuracy was better than < or =1.5%, compared with errors of up to 7.5% with a standard algorithm. For a 20-step intensity modulated field, the accuracy was 3.4% compared with 18% with the conventional algorithm. The advantages of this model for IMRT are discussed.
M H Phillips; K M Singer; A R Hounsell
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Publication Detail:
Type:  Journal Article; Research Support, Non-U.S. Gov't    
Journal Detail:
Title:  Physics in medicine and biology     Volume:  44     ISSN:  0031-9155     ISO Abbreviation:  Phys Med Biol     Publication Date:  1999 Apr 
Date Detail:
Created Date:  1999-07-28     Completed Date:  1999-07-28     Revised Date:  2006-11-15    
Medline Journal Info:
Nlm Unique ID:  0401220     Medline TA:  Phys Med Biol     Country:  ENGLAND    
Other Details:
Languages:  eng     Pagination:  1067-88     Citation Subset:  IM    
Department of Radiation Oncology, University of Washington Medical Center, Seattle 98195-6043, USA.
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MeSH Terms
Models, Statistical*
Phantoms, Imaging
Radiotherapy Planning, Computer-Assisted
Radiotherapy, Computer-Assisted / instrumentation*,  methods*

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