title: Dosimetric properties of a flattening filter-free 6-MV photon beam: a Monte Carlo study.
abstract: OBJECTIVE
  The dosimetric features of an unflattened 6-MV photon beam of an Elekta SL-25 linac was calculated by the Monte Carlo (MC) method.
  
  
  METHODS
  The head of the Elekta SL-25 linac was simulated using the MCNP4C MC code. The accuracy of the model was evaluated using measured dosimetric features, including depth dose values and dose profiles in a water phantom. The flattening filter was then removed, and beam dosimetric properties were calculated by the MC method and compared with those of the flattened photon beam.
  
  
  RESULTS
  Our results showed a significant (twofold) increase in the dose rate for all field sizes. Also, the photon beam spectra for an unflattened beam were softer, which led to a steeper reduction in depth doses. The decrease in the out-of-field dose and increase in the contamination electrons and a buildup region dose were the other consequences of removing the flattening filter.
  
  
  CONCLUSIONS
  Our study revealed that, for recent radiotherapy techniques, the use of multileaf collimators for beam shaping removing the flattening filter could offer some advantages, including an increased dose rate and decreased out-of-field dose.
authors: Medical Physics Department, Medical School, Tabriz University of Medical Sciences, Attare Nishabouri Street, Tabriz, Iran. asgharmesbahi@yahoo.com
authors: Asghar
authors: A
authors: Mesbahi
authors: Parinaz
authors: P
authors: Mehnati
authors: Ahmad
authors: A
authors: Keshtkar
authors: Alireza
authors: A
authors: Farajollahi
mesh_terms: D009010:Monte Carlo Method; D010315:Particle Accelerators; D019047:Phantoms, Imaging; D017785:Photons; D011829:Radiation Dosage; D012542:Scattering, Radiation
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