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Author Wroe, A. ♦ Slater, J. ♦ McAuley, G.
Source United States Department of Energy Office of Scientific and Technical Information
Content type Text
Language English
Subject Keyword APPLIED LIFE SCIENCES ♦ RADIATION PROTECTION AND DOSIMETRY ♦ BETA PARTICLES ♦ BORATES ♦ COMPUTERIZED SIMULATION ♦ DOSE EQUIVALENTS ♦ DOSEMETERS ♦ EVALUATION ♦ FAST NEUTRONS ♦ LUMINESCENCE ♦ MICRODOSIMETRY ♦ MONTE CARLO METHOD ♦ PATIENTS ♦ POLYETHYLENES ♦ PROTON BEAMS ♦ RADIATION DOSES ♦ RADIOTHERAPY ♦ SHIELDING ♦ THERMAL NEUTRONS
Abstract Purpose: To design, implement and evaluate a shielding system that will reduce out-of-field dose experienced by the patient and associated electronic systems in passively scattered proton therapy treatment. Methods: A multi-stage neutron shielding system was retrofitted to the Gantry 1 treatment nozzle at Loma Linda University Medical Center. The system uses multiple borated polyethylene plates staged after the primary beam modifying devices to attenuate and absorb neutrons produced by such devices. This arrangement locates increasing levels of shielding between the sources of secondary particles in the nozzle and the patient. Additionally, the design of this shielding structure allows it to be easily retrofitted to an existing proton nozzle system without impacting design or treatment beam characteristics. The effectiveness of the shielding was evaluated both through experimental measurements and Geant4 Monte Carlo simulations. Results: Measurements were completed with Landauer Luxel+ dosimeters that use optically stimulated luminescence and CR-39 to detect fast neutrons, thermal neutrons, protons, photons and beta particles. Measurements of a 250 MeV proton beam indicated that the shielding system reduced out-of-field dose to the patient by almost half with dose equivalent values at 50 and 40 cm from the field edge decreasing from 0.965 and 1.262 mSv/Gy to 0.596 and 0.777 mSv/Gy respectively. The installation of the multi-stage shielding system also reduced dose equivalent experienced by electronic systems installed in the treatment room by up to 80%. Geant4 simulations were also used to evaluate the neutron fluence at various positions in the treatment room as well as provide information on microdosimetry spectra within the patient and treatment room. Conclusion: The shielding system described above proved to be an effective an inexpensive method of reducing out-of-field doses to the patient and electronic systems and can be easily retrofitted to existing passive scattering nozzles.
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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