Medical Radiology and Radiation Safety. 2019. Vol. 64. No. 3. P. 78–84

DOI: 10.12737/article_5cf3e86a478d20.08095360

E.N. Lykova^1,2, M.V. Zheltonozhskaya^1,2, F.Yu. Smirnov³, P.I. Rudnev⁴, A.P. Chernyaev^1,2, I.V. Cheshigin⁵, V.N. Yatsenko³

Analysis of the Bremsstrahlung Photons Flux and the Neutrons Beams during the Operation of an Electrons Medical Accelerator

1. Faculty of Physics, M.V. Lomonosov Moscow State University, Moscow, Russia. E-mail: This email address is being protected from spambots. You need JavaScript enabled to view it. ;
2. D.V. Skobeltsyn Institute of Nuclear Physics, M.V. Lomonosov Moscow State University, Moscow, Russia;
3. A.I. Burnasyan Federal Medical Biophysical Center, Moscow, Russia;
4. LLC “Center ATSP”, Moscow, Russia;
5. National Research Center «Kurchatov Institute», Moscow, Russia

E.N. Lykova – Senior Lecturer;
M.V. Zheltonozhskaya – Senior Researcher, PhD Tech.;
F.Yu. Smirnov – Medical Physicist;
P.I. Rudnev – Director;
A.P. Chernyaev – Head of Dep., Dr. Sci. Phys.-Math., Prof.;
I.V. Cheshigin – Senior Researcher;
V.N. Yatsenko – Head of Lab., PhD Tech.

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.

Key words: radiation therapy, bremstrahlung, photonuclear reactions, secondary neutrons, activation method

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For citation: Lykova EN, Zheltonozhskaya MV, Smirnov FYu, Rudnev PI, Chernyaev AP, Cheshigin IV, Yatsenko VN. Analysis of the Bremsstrahlung Photons Flux and the Neutrons Beams during the Operation of an Electrons Medical Accelerator. Medical Radiology and Radiation Safety. 2019;64(3):78-84. (Russian).

DOI: 10.12737/article_5cf3e86a478d20.08095360

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