title: Monte Carlo simulation of a dynamic MLC: implementation and applications.
abstract: OBJECTIVE
  Study of behavior and influence of a multileaf collimator (MLC) on dose calculation, verification, and portal energy spectra in the case of intensity-modulated fields obtained with a step-and-shoot or a dynamic technique.
  
  
  METHODS
  The 80-leaf MLC for the Varian Clinac 2300 C/D was implemented in a previously developed Monte Carlo (MC) based multiple source model (MSM) for a 6 MV photon beam. Using this model and the MC program GEANT, dose distributions, energy fluence maps and energy spectra at different portal planes were calculated for three different MLC applications.
  
  
  RESULTS
  The comparison of MC-calculated dose distributions in the phantom and portal plane, with those measured with films showed an agreement within 3% and 1.5 mm for all cases studied. The deviations mainly occur in the extremes of the intensity modulation. The MC method allows to investigate, among other aspects, dose components, energy fluence maps, tongue-and-groove effects and energy spectra at portal planes.
  
  
  CONCLUSIONS
  The MSM together with the implementation of the MLC is appropriate for a number of investigations in intensity-modulated radiation therapy (IMRT).
authors.affiliation: Institute for Biomedical Engineering, University of Zurich and ETH.
authors.forename: M K
authors.initials: MK
authors.lastname: Fix
authors.forename: P
authors.initials: P
authors.lastname: Manser
authors.forename: E J
authors.initials: EJ
authors.lastname: Born
authors.forename: D
authors.initials: D
authors.lastname: Vetterli
authors.forename: R
authors.initials: R
authors.lastname: Mini
authors.forename: P
authors.initials: P
authors.lastname: Rüegsegger
mesh_terms: D003198:Computer Simulation; D006801:Humans; D009010:Monte Carlo Method; D019047:Phantoms, Imaging; D017785:Photons / Q000627:therapeutic use; D011880:Radiotherapy Planning, Computer-Assisted / Q000379:methods*; D015203:Reproducibility of Results