期刊
PHYSICS IN MEDICINE AND BIOLOGY
卷 54, 期 4, 页码 993-1008出版社
IOP PUBLISHING LTD
DOI: 10.1088/0031-9155/54/4/012
关键词
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资金
- National Science Foundation [0320708]
- National Institute of Health Ruth L Kirschstein National Research Service Award Individual Predoctoral Fellowship Program [F31 CA119943-03]
- Northern Illinois University through a Department of Defense [W81XWH-08-1-0205]
- Direct For Computer & Info Scie & Enginr
- Division Of Computer and Network Systems [0320708] Funding Source: National Science Foundation
In this work the neutron production in a passive beam delivery system was investigated. Secondary particles including neutrons are created as the proton beam interacts with beam shaping devices in the treatment head. Stray neutron exposure to the whole body may increase the risk that the patient develops a radiogenic cancer years or decades after radiotherapy. We simulated a passive proton beam delivery system with double scattering technology to determine the neutron production and energy distribution at 200 MeV proton energy. Specifically, we studied the neutron absorbed dose per therapeutic absorbed dose, the neutron absorbed dose per source particle and the neutron energy spectrum at various locations around the nozzle. We also investigated the neutron production along the nozzle's central axis. The absorbed doses and neutron spectra were simulated with the MCNPX Monte Carlo code. The simulations revealed that the range modulation wheel (RMW) is the most intense neutron source of any of the beam spreading devices within the nozzle. This finding suggests that it may be helpful to refine the design of the RMW assembly, e. g., by adding local shielding, to suppress neutron-induced damage to components in the nozzle and to reduce the shielding thickness of the treatment vault. The simulations also revealed that the neutron dose to the patient is predominated by neutrons produced in the field defining collimator assembly, located just upstream of the patient.
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