title: Design and simulation of a short, variable-energy 4 to 10 MV S-band linear accelerator waveguide.
abstract: OBJECTIVE
  To modify a previously designed, short, 10 MV linac waveguide, so that it can produce any energy from 4 to 10 MV. The modified waveguide is designed to be a drop-in replacement for the 6 MV waveguide used in the author's current linear accelerator-magnetic resonance imager (Linac-MR).
  
  
  METHODS
  Using our group's previously designed short 10 MV linac as a starting point, the port was moved to the fourth cavity, the shift to the first coupling cavity was removed and a tuning cylinder added to the first coupling cavity. Each cavity was retuned using finite element method (FEM) simulations to resonate at the desired frequency. FEM simulations were used to determine the RF field distributions for various tuning cylinder depths, and electron trajectories were computed using a particle-in-cell model to determine the required RF power level and tuning cylinder depth to produce electron energy distributions for 4, 6, 8, and 10 MV photon beams. Monte Carlo simulations were then used to compare the depth dose profiles with those produced by published electron beam characteristics for Varian linacs.
  
  
  RESULTS
  For each desired photon energy, the electron beam energy was within 0.5% of the target mean energy, the depth of maximum dose was within 1.5 mm of that produced by the Varian linac, and the ratio of dose at 10 cm depth to 20 cm depth was within 1%.
  
  
  CONCLUSIONS
  A new 27.5 cm linear accelerator waveguide design capable of producing any photon energy between 4 and 10 MV has been simulated, however coupling port design and the implications of increased electron beam current at 10 MV remain to be investigated. For the specific cases of 4, 6, and 10 MV, this linac produces depth dose profiles similar to those produced by published spectra for Varian linacs.
authors.affiliation: Medical Physics Division, Department of Oncology, University of Alberta, 11560 University Avenue, Edmonton, Alberta, T6G 1Z2, Canada.
authors.forename: Devin
authors.initials: D
authors.lastname: Baillie
authors.affiliation: Medical Physics Division, Department of Oncology, University of Alberta, 11560 University Avenue, Edmonton, Alberta, T6G 1Z2, Canada.|Department of Physics, University of Alberta, 11322 - 89 Avenue, Edmonton, Alberta, T6G 2G7, Canada.|Department of Medical Physics, Cross Cancer Institute, 11560 University Avenue, Edmonton, Alberta, T6G 1Z2, Canada.
authors.forename: B Gino
authors.initials: BG
authors.lastname: Fallone
authors.affiliation: Medical Physics Division, Department of Oncology, University of Alberta, 11560 University Avenue, Edmonton, Alberta, T6G 1Z2, Canada.|Department of Medical Physics, Cross Cancer Institute, 11560 University Avenue, Edmonton, Alberta, T6G 1Z2, Canada.
authors.forename: Stephen
authors.initials: S
authors.lastname: Steciw
mesh_terms: D004583:Electrons; D006801:Humans; D009010:Monte Carlo Method; D010315:Particle Accelerators; D017785:Photons
keywords: S-band; linac-MR; linear accelerator; radiation therapy; variable energy; x-ray production