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Author Horst, F. ♦ Czarnecki, D. ♦ Zink, K.
Source United States Department of Energy Office of Scientific and Technical Information
Content type Text
Language English
Subject Keyword RADIATION PROTECTION AND DOSIMETRY ♦ RADIOLOGY AND NUCLEAR MEDICINE ♦ COMPUTERIZED SIMULATION ♦ DEPTH DOSE DISTRIBUTIONS ♦ ELECTRONS ♦ FAST NEUTRONS ♦ LINEAR ACCELERATORS ♦ MEV RANGE 01-10 ♦ MONTE CARLO METHOD ♦ NEUTRON TRANSPORT ♦ PATIENTS ♦ PHOTONS ♦ PHOTONUCLEAR REACTIONS ♦ RADIATION PROTECTION ♦ RADIOTHERAPY
Abstract Purpose: Today the majority of radiation therapy treatments are performed at medical electron linear accelerators (linacs). The accelerated electrons are used for the generation of bremsstrahlung photons. The use of higher electron respectively photon energies has some advantages over lower energies such as the longer dose build-up. However photons with energies higher than ∼7 MeV can additionally to the interaction with bound electrons undergo inelastic reactions with nuclei. These photonuclear reactions lead to the emission of fast neutrons which contaminate the primary photon field. The neutrons might penetrate through the collimators and deliver out-of-field dose to the patient. Furthermore the materials inside the linac head as well as the air inside the treatment room get activated which might deliver dose to the medical employees even when the linac is not in operation. A detailed knowledge of these effects is essential for adequate radiation protection of the employees and an optimal patient treatment. Methods: It is a common method to study the radiation fields of such linacs by means of Monte Carlo simulations. For the investigation of the effects caused by photonuclear reactions a typical linac in high energy mode (Varian Clinac 18 MV-X) as well as the surrounding bunker were modelled and simulated using the Monte Carlo code FLUKA which includes extensive nuclear reaction and neutron transport models additional to electron-photon transport as well as capabilities for a detailed study of effective dose distributions and activation yields. Results: Neutron spectra as well as neutron effective dose distributions within the bunker were obtained, reaching up to some mSv/Gy in the patient’s plane. The results are normalized per Gy in the depth dose maximum at 10×10 cm{sup 2} field size. Therefore an absolute interpretation is possible. Conclusion: The obtained data gives a better understanding of the photonuclear reaction caused effects.
ISSN 00942405
Educational Use Research
Learning Resource Type Article
Publisher Date 2015-06-15
Publisher Place United States
Journal Medical Physics
Volume Number 42
Issue Number 6


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