title: Estimation of photoneutron yield in linear accelerator with different collimation systems by Geant4 and MCNPX simulation codes.
abstract: At present, the bremsstrahlung photon beams produced by linear accelerators are the most commonly employed method of radiotherapy for tumor treatments. A photoneutron source based on three different energies (6, 10 and 15 MeV) of a linac electron beam was designed by means of Geant4 and Monte Carlo N-Particle eXtended (MCNPX) simulation codes. To obtain maximum neutron yield, two arrangements for the photo neutron convertor were studied: (a) without a collimator, and (b) placement of the convertor after the collimator. The maximum photon intensities in tungsten were 0.73, 1.24 and 2.07 photon/e at 6, 10 and 15 MeV, respectively. There was no considerable increase in the photon fluence spectra from 6 to 15 MeV at the optimum thickness between 0.8 mm and 2 mm of tungsten. The optimum dimensions of the collimator were determined to be a length of 140 mm with an aperture of 5 mm  ×  70 mm for iron in a slit shape. According to the neutron yield, the best thickness obtained for the studied materials was 30 mm. The number of neutrons generated in BeO achieved the maximum value at 6 MeV, unlike that in Be, where the highest number of neutrons was observed at 15 MeV. Statistical uncertainty in all simulations was less than 0.3% and 0.05% for MCNPX and the standard electromagnetic (EM) physics packages of Geant4, respectively. Differences among spectra in various regions are due to various cross-section and stopping power data and different simulations of the physics processes.
authors.affiliation: Department of Computer Science and Engineering, Korea University of Technology and Education, Cheonan, Korea.
authors.forename: Yoon Sang
authors.initials: YS
authors.lastname: Kim
authors.forename: Zeinab
authors.initials: Z
authors.lastname: Khazaei
authors.forename: Junho
authors.initials: J
authors.lastname: Ko
authors.forename: Hossein
authors.initials: H
authors.lastname: Afarideh
authors.forename: Mitra
authors.initials: M
authors.lastname: Ghergherehchi
mesh_terms: D000465:Algorithms; D009502:Neutrons; D010315:Particle Accelerators / Q000295:instrumentation*; D017785:Photons; D011880:Radiotherapy Planning, Computer-Assisted / Q000379:methods*