title: Portal verification of high-energy electron beams using their photon contamination by film-cassette systems.
abstract: OBJECTIVE
  Though electron beams are widely used in radiotherapy, their verification is not well established in clinical practice. The present study compares the suitability of several sensitive film-cassette systems for electron-portal verification by contaminating photons.
  
  
  METHODS
  The characteristics of the optical density curves of film-cassette combinations were determined by exposing them to the bremsstrahlung contamination of a variety of electron beams. Using a Las-Vegas Phantom the spatial low-contrast resolution of the combinations was investigated. The absorbed dose rates due to the contaminant photons were measured for different geometric conditions.
  
  
  RESULTS
  Suitable film-cassette combinations were found for portal verification of all usual electron energies. The best image quality was obtained using the EC film and the EC-L cassettes. For electron energies higher than 6 MeV some film-cassette combinations are suitable to verify abutted electron and photon portals using the same film sheet.
  
  
  CONCLUSIONS
  The verification of electron portals and of abutted electron-photon portals can be performed by sensitive film-cassette systems with an image quality comparable to photon-beam verification.
authors.affiliation: Department of Radiotherapy and Radiooncology, University Hospital Carl Gustav Carus, University of Technology, Dresden, Germany. peter.geyer@mailbox.tu-dresden.de
authors.forename: Peter
authors.initials: P
authors.lastname: Geyer
authors.forename: Wolfgang W
authors.initials: WW
authors.lastname: Baus
authors.forename: Michael
authors.initials: M
authors.lastname: Baumann
mesh_terms: D003720:Densitometry; D004583:Electrons; D005373:Film Dosimetry / Q000379:methods*; D006801:Humans; D008962:Models, Theoretical; D009040:Motion Pictures; D019047:Phantoms, Imaging; D017785:Photons; D011786:Quality Control; D011874:Radiometry / Q000379:methods*; D011878:Radiotherapy; D014962:X-Ray Film