title: Monte Carlo modelling of a virtual wedge.
abstract: Compared with a set of physical photon wedges, a non physical wedge (virtual or dynamic wedge), realized by a moving collimator jaw, offers an alternative that allows creation of a wedged field with any arbitrary wedge angle instead of the traditional four physical wedges (15 degrees, 30 degrees, 45 degrees and 60 degrees). It is commonly assumed that non-physical wedges do not alter the photon spectrum compared with physical wedges that introduce beam hardening and loss of dose uniformity in the unwedged direction. In this study, we investigated the influence of a virtual wedge on the photon spectra of a 6-10 MV Siemens MD2 accelerator with the Monte Carlo code EGS4/BEAM. Good agreement was obtained between calculated and measured lateral dose profiles at the depth of maximum dose and at 10 cm depth for 20 x 20 cm2 fields for 6 and 10 MV photon beams. By comparing Monte Carlo models of a physical wedge and the virtual wedge that was studied in this work, it is confirmed that the latter has an insignificant effect on the beam quality, whereas the former can introduce significant beam hardening.
authors.affiliation: Physics Department, Royal Marsden Hospital (Institute of Cancer Research), London, UK. f.verhaegen@icr.ac.uk
authors.forename: F
authors.initials: F
authors.lastname: Verhaegen
authors.forename: I J
authors.initials: IJ
authors.lastname: Das
mesh_terms: D003198:Computer Simulation; D009010:Monte Carlo Method; D010315:Particle Accelerators / Q000295:instrumentation; D017785:Photons; D014414:Tungsten / Q000737:chemistry
chemical_list: D014414:Tungsten