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Portal verification of high-energy electron beams using their photon contamination by film-cassette systems
Peter Geyer1, Wolfgang W Baus, Michael Baumann
1Department of Radiotherapy and Radiooncology, University Hospital Carl Gustav Carus, University of Technology, Dresden, Germany. peter.geyer@mailbox.tu-dresden.de
Background And Purpose:
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.
Material And 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.
Conclusion:
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.
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