title: A Monte Carlo study of a flattening filter-free linear accelerator verified with measurements.
abstract: A Monte Carlo model of an Elekta Precise linear accelerator has been built and verified by measured data for a 6 and 10 MV photon beam running with and without a flattening filter in the beam line. In this study the flattening filter was replaced with a 6 mm thick copper plate, provided by the linac vendor, in order to stabilize the beam. Several studies have shown that removal of the filter improves some properties of the photon beam, which could be beneficial for radiotherapy treatments. The investigated characteristics of this new beam included output, spectra, mean energy, half value layer and the origin of scattered photons. The results showed an increased dose output per initial electron at the central axis of 1.76 and 2.66 for the 6 and 10 MV beams, respectively. The number of scattered photons from the accelerator head was reduced by (31.7 ± 0.03)% (1 SD) for the 6 MV beam and (47.6 ± 0.02)% for the 10 MV beam. The photon energy spectrum of the unflattened beam was softer compared to a conventional beam and did not vary significantly with the off-axis distance, even for the largest field size (0-20 cm off-axis).
authors.affiliation: Radiation Physics, Skåne University Hospital and Lund University, Lund, Sweden. marten.dalaryd@skane.se
authors.forename: Mårten
authors.initials: M
authors.lastname: Dalaryd
authors.forename: Gabriele
authors.initials: G
authors.lastname: Kragl
authors.forename: Crister
authors.initials: C
authors.lastname: Ceberg
authors.forename: Dietmar
authors.initials: D
authors.lastname: Georg
authors.forename: Brendan
authors.initials: B
authors.lastname: McClean
authors.forename: Sacha
authors.initials: S
authors.lastname: af Wetterstedt
authors.forename: Elinore
authors.initials: E
authors.lastname: Wieslander
authors.forename: Tommy
authors.initials: T
authors.lastname: Knöös
mesh_terms: D003300:Copper; D009010:Monte Carlo Method; D017785:Photons; D012542:Scattering, Radiation
chemical_list: D003300:Copper