title: Radiation transport calculations for 50 MV photon therapy beam using the Monte Carlo code GEANT4.
abstract: A new thin transmission target technique for fast dose delivery using narrow scanned photon beams has been developed. High-energy, 50-100 MeV, electron beams of low emittance incident on thin low-Z targets produce narrow and intense high-energy bremsstrahlung beams. However, electrons transmitted through the target are bent from the therapeutic beam by a purging magnet and have to be effectively absorbed in a dedicated electron collector. The electron-photon transport through a treatment head has been studied using the Monte Carlo simulation toolkit Geant4. The Geant4 electromagnetic physics processes have been compared with experimental data of radial dose profiles. The differences between calculated and measured radial dose distributions are approximately 2-10%. Preliminary investigations of the collector design have been carried out in order to minimise secondary electron and photon contamination of the therapeutic beam. The toolkit presented here is promising for further development of narrow photon beam therapy.
authors.affiliation: Department of Medical Radiation Physics, Karolinska Institutet and Stockholm University, P.O. Box 260, S-171 76 Stockholm, Sweden. Susanne.Larsson@radfys.ki.se
authors.forename: Susanne
authors.initials: S
authors.lastname: Larsson
authors.forename: Roger
authors.initials: R
authors.lastname: Svensson
authors.forename: Irena
authors.initials: I
authors.lastname: Gudowska
authors.forename: Vladimir
authors.initials: V
authors.lastname: Ivanchenko
authors.forename: Anders
authors.initials: A
authors.lastname: Brahme
mesh_terms: D003198:Computer Simulation; D006801:Humans; D018499:Linear Energy Transfer; D008954:Models, Biological; D015233:Models, Statistical; D009010:Monte Carlo Method; D017785:Photons / Q000627:therapeutic use*; D011874:Radiometry / Q000379:methods*; D011879:Radiotherapy Dosage; D011880:Radiotherapy Planning, Computer-Assisted / Q000379:methods*; D012542:Scattering, Radiation; D012984:Software; D012986:Software Validation