Analysis of the Bremsstrahlung Photons Flux and the Neutrons Beams during the Operation of the Medical Electron Accelerator
Author:
Лыкова Е.1, Lykova E.2, Желтоножская М.11, Zheltonozhskaya M.22, Смирнов Ф.3, Smirnov F.4, Руднев П.5, Rudnev P.6, Черняев А.1, Chernyaev A.2, Чешигин И.7, Cheshigin I.8, Яценко В.3, Yatsenko V.4
Affiliation:
1. Московский государственный университет имени М.В. Ломоносова 2. M.V. Lomonosov Moscow State University 3. Федеральный медицинский биофизический центр им. А.И. Бурназяна ФМБА России 4. A.I. Burnasyan Federal Medical Biophysical Center of FMBA 5. ООО «Центр АЦП» 6. LLC "Center ATSP" 7. Национальный Исследовательский Центр «Курчатовский институт» 8. National Research Center «Kurchatov Institute»,
Abstract
Purpose: To estimate the contribution of the secondary neutron flux to the total radiation flux during the operation of Trilogy linear medical accelerator and Varian’s Clinac 2100 accelerator for assessment of impact on the health of patients and medical personnel.
High-energy linear accelerators operating at energies higher than 8 MeV generate neutron fluxes when interacting with accelerator elements and with structural materials of the room for treating patients. Neutrons can form at the accelerator head (target, collimators, smoothing filter, etc.), the procedure room, and directly in the patient’s body.
Because of the high radiobiological hazard of neutron radiation, its contribution to the total beam flux, even at a level of few percent, substantially increases the dose received by the patient.
Material and methods: Secondary neutron fluxes were investigated during the process of the linear medical accelerators Trilogy and Clinac 2100 of Varian operation by the photoactivation method using (γ, n) and (n, γ) reactions on the detection target of natural 181Ta. In addition, measurements of neutron spectra were carried out directly in the room during the operation of a medical accelerator using a spectrometer-dosimeter SDMF-1608.
Results: It was determined that the neutron flux on the tantalum target is 16 % of the gamma-ray flux on the same target when the accelerator is operated with a 18 MeV bremsstrahlung energy and 5 % when the accelerator is operated with a 20 MeV excluding thermal neutrons.
Conclusion: Finally, it may be noted that, taking into account the coefficient of relative biological efficiency (RBE) of neutron radiation for neutrons with energies of 0.1–200 keV equal to 10 compared with the RBE coefficient for gamma quanta (equal to 1), even preliminary analysis demonstrates significant underestimation of the contribution of neutrons dose to the total dose received by the patient in radiation therapy using bremsstrahlung of 18 and 20 MeV.
Publisher
Infra-M Academic Publishing House
Subject
Nuclear Energy and Engineering
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