Monte Carlo study of photon fields from a flattening filter-free clinical accelerator

Journal Article · Sat Apr 15 04:00:00 EDT 2006 · Medical Physics

DOI:https://doi.org/10.1118/1.2174720· OSTI ID:20775121

Vassiliev, Oleg N; Titt, Uwe; Kry, Stephen F; Poenisch, Falk; Gillin, Michael T; Mohan, Radhe ^[1]

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1. University of Texas M. D. Anderson Cancer Center, 1515 Holcombe Boulevard, Houston, Texas 77030 (United States)

In conventional clinical linear accelerators, the flattening filter scatters and absorbs a large fraction of primary photons. Increasing the beam-on time, which also increases the out-of-field exposure to patients, compensates for the reduction in photon fluence. In recent years, intensity modulated radiation therapy has been introduced, yielding better dose distributions than conventional three-dimensional conformal therapy. The drawback of this method is the further increase in beam-on time. An accelerator with the flattening filter removed, which would increase photon fluence greatly, could deliver considerably higher dose rates. The objective of the present study is to investigate the dosimetric properties of 6 and 18 MV photon beams from an accelerator without a flattening filter. The dosimetric data were generated using the Monte Carlo programs BEAMnrc and DOSXYZnrc. The accelerator model was based on the Varian Clinac 2100 design. We compared depth doses, dose rates, lateral profiles, doses outside collimation, total and collimator scatter factors for an accelerator with and without a flatteneing filter. The study showed that removing the filter increased the dose rate on the central axis by a factor of 2.31 (6 MV) and 5.45 (18 MV) at a given target current. Because the flattening filter is a major source of head scatter photons, its removal from the beam line could reduce the out-of-field dose.

• OSTI ID: 20775121
• Journal Information: Medical Physics, Journal Name: Medical Physics Journal Issue: 4 Vol. 33; ISSN 0094-2405; ISSN MPHYA6
• Country of Publication: United States
• Language: English

Related Subjects

61 RADIATION PROTECTION AND DOSIMETRY
COLLIMATORS
DEPTH DOSE DISTRIBUTIONS
DOSE RATES
DOSIMETRY
FILTERS
LINEAR ACCELERATORS
MONTE CARLO METHOD
PATIENTS
PHOTON BEAMS
PHOTONS
RADIATION DOSES
RADIOTHERAPY