title: Modeling a complex micro-multileaf collimator using the standard BEAMnrc distribution.
abstract: OBJECTIVE
  The component modules in the standard BEAMnrc istribution may appear to be insufficient to model micro-multileaf collimators that have trifaceted leaf ends and complex leaf profiles. This note indicates, however, that accurate Monte Carlo simulations of radiotherapy beams defined by a complex collimation device can be completed using BEAMnrc's standard VARMLC component module.
  
  
  METHODS
  That this simple collimator model can produce spatially and dosimetrically accurate microcollimated fields is illustrated using comparisons with ion chamber and film measurements of the dose deposited by square and irregular fields incident on planar, homogeneous water phantoms.
  
  
  RESULTS
  Monte Carlo dose calculations for on-axis and off-axis fields are shown to produce good agreement with experimental values, even on close examination of the penumbrae.
  
  
  CONCLUSIONS
  The use of a VARMLC model of the micro-multileaf collimator, along with a commissioned model of the associated linear accelerator, is therefore recommended as an alternative to the development or use of in-house or third-party component modules for simulating stereotactic radiotherapy and radiosurgery treatments. Simulation parameters for the VARMLC model are provided which should allow other researchers to adapt and use this model to study clinical stereotactic radiotherapy treatments.
authors.affiliation: School of Physical and Chemical Sciences, Queensland University of Technology, G.PO. Box 2434, Brisbane, Queensland 4001, Australia. kairn@physics.org
authors.forename: T
authors.initials: T
authors.lastname: Kairn
authors.forename: J
authors.initials: J
authors.lastname: Kenny
authors.forename: S B
authors.initials: SB
authors.lastname: Crowe
authors.forename: A L
authors.initials: AL
authors.lastname: Fielding
authors.forename: R D
authors.initials: RD
authors.lastname: Franich
authors.forename: P N
authors.initials: PN
authors.lastname: Johnston
authors.forename: R T
authors.initials: RT
authors.lastname: Knight
authors.forename: C M
authors.initials: CM
authors.lastname: Langton
authors.forename: D
authors.initials: D
authors.lastname: Schlect
authors.forename: J V
authors.initials: JV
authors.lastname: Trapp
mesh_terms: D000465:Algorithms; D003198:Computer Simulation; D004867:Equipment Design; D005373:Film Dosimetry / Q000379:methods*; D006801:Humans; D009010:Monte Carlo Method; D010315:Particle Accelerators; D019047:Phantoms, Imaging; D011829:Radiation Dosage; D016634:Radiosurgery / Q000379:methods; D011880:Radiotherapy Planning, Computer-Assisted / Q000295:instrumentation; D015203:Reproducibility of Results; D012984:Software; D014867:Water / Q000737:chemistry
chemical_list: D014867:Water