Document Detail

Out-of-field photon dose following removal of the flattening filter from a medical accelerator.
MedLine Citation:
PMID:  20305334     Owner:  NLM     Status:  MEDLINE    
The aim of this paper is to determine the effect of removing the flattening filter from a linear accelerator on the out-of-field photon dose. A Monte Carlo model was used to simulate 6 MV and 18 MV photon beams from a Varian 2100 accelerator with the flattening filter in place and with it removed. The out-of-field photon doses and composition (head leakage, patient scatter and collimator scatter) were calculated from square open fields in a water tank as a function of distance from central axis, field size and depth. The out-of-field doses resulting from intensity-modulated radiation therapy to the prostate at 6 MV were also calculated, with and without the flattening filter, to sensitive organs in an anthropomorphic Rando phantom. Removal of the flattening filter reduced the out-of-field dose near the treatment field (<3 cm from the field edge) because of decreased collimator scatter. It increased the out-of-field dose at intermediate distances from the field edge (3-15 cm) because of increased patient scatter. At greater distances, the out-of-field dose was decreased because of reduced head leakage. For the clinical treatment examined, the out-of-field dose was generally reduced following removal of the flattening filter, particularly at large distances from the treatment field. Removal of the flattening filter may be advantageous by reducing the out-of-field dose to the patient. This could contribute to reducing the long-term risk of secondary malignancies. In general, however, the out-of-field dose depends on treatment and patient parameters, and a reduction may not always be achievable.
Stephen F Kry; Oleg N Vassiliev; Radhe Mohan
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Publication Detail:
Type:  Journal Article     Date:  2010-03-19
Journal Detail:
Title:  Physics in medicine and biology     Volume:  55     ISSN:  1361-6560     ISO Abbreviation:  Phys Med Biol     Publication Date:  2010 Apr 
Date Detail:
Created Date:  2010-04-02     Completed Date:  2010-06-22     Revised Date:  -    
Medline Journal Info:
Nlm Unique ID:  0401220     Medline TA:  Phys Med Biol     Country:  England    
Other Details:
Languages:  eng     Pagination:  2155-66     Citation Subset:  IM    
Department of Radiation Physics, The University of Texas MD Anderson Cancer Center, Houston, TX, USA.
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MeSH Terms
Monte Carlo Method
Neutrons / therapeutic use
Photons / therapeutic use*
Radiation Dosage*
Radiotherapy / instrumentation*,  methods*
Radiotherapy Dosage

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