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

DOI: 10.12737/article_5cf3e86a478d20.08095360

E.N. Lykova1,2, M.V. Zheltonozhskaya1,2, F.Yu. Smirnov3, P.I. Rudnev4, A.P. Chernyaev1,2, 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.


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


  1. Carrillo HR, Almaraz BH, Dávila VM, Hernández AO. Neutron spectrum and doses in a 18 MV Linac. J Radioanal Nucl Chem. 2010;283:261-5.

  2. Zanini A, Durisi E, Fasolo F, Ongaro C, Visca L, Nastasi U, et al. Monte Carlo simulation of the photoneutron field in linac radiotherapy treatments with different collimation systems. Phys Med Biol. 2004;49:571-82.

  3. Pena J, Franco L, Gómez F, Iglesias A, Pardo J, Pombar M. Monte Carlo study of Siemens PRIMUS photoneutron production. Phys Med Biol. 2005;50:5921-33.

  4. Seltzer SM. An assessment of the role of charged seconderies from nonelastic nuclear interaction by therapy proton beam in water. National Institute of Standards and Tehnology Technical Reports No. NISTIR 5221, 1993.

  5. Schimmerling W, Rapkin M, Wong M, Howard J. The propagation of relativistic heavy ions in multielement beam lines. Med Phys. 1986;13:217-23.

  6. Varzar SM, Tultaev AV, Chernyaev AP. The role of secondary particles in the passage of ionizing radiation through biological media. Med Fizika . 2001;9:58-67. (Russian).

  7. Satherberg A, Johansson L. Photonuclear production in tissue for different 50 MV bremstrahlung beams. Med Phys. 1998;25:683.

  8. Allen PD, Chaudhri MA. The dose contribution due to photonuclear reaction during radioterapy. Med Phys. 1982;9:904.

  9. Spurny F, Johansson L, Satherberg A, Bednar J, Turek K. The contribution of secondery heavy particles to the absorbed dose from high energy photon beam. Phys Med Biol. 1996;41:2643.

  10. Ahnesjo A, Weber L, Nilsson P. Modeling transmission and scatter or photon beam attenuator. Med Phys. 1995;22:1711.

  11. Gottschalk B, Platais R, Paganetti H. Nuclear interaction of 160 MeV protons stopping in copper: a test of Monte Carlo nuclear models. Med Phys. 1999;26:2597.

  12. Carlsson CA, Carlsson GA. Proton dosimetry with 185 MeV protons: dose buildup from secondery protons recoil electrons. Health Phys. 1977;33:481.

  13. Deasy JO. A proton dose calculation algorithm for conformal therapy simulations based on Molieres theory of lateral deflections. Phys Med. 1998;25:476.

  14. Hassan Ali Nedaie, Hoda Darestani, Nooshin Banaee, Negin Shagholi, Kheirollah Mohammadi, Arjang Shahvar et al. Neutron dose measurements of Varian and Elekta linacs by TLD600 and TLD700 dosimeters and comparison with MCNP calculations. J Med Phys 2014;39(1):10-17.

  15. Hashemi SM, Hashemi-Malayeri B, Raisali G, Shokrani P, Sharafi AA. A study of the photoneutron dose equivalent resulting from a Saturne 20 medical linac using Monte Carlo method. Nukleonika; 2007;52:39-43.

  16. PTW Freiburg GmbH, Germany. Available from: rw3_slab_phantoms0.html.

  17. Alireza Naseria, Asghar Mesbahia. A review on photoneutrons characteristics in radiation therapy with high-energy photon beams. Rep Practical Oncol Radiother. 2010;15:138-44.

  18. Sellin PJ, Jaffar G, Jastaniah SD. Performance of digital algorithms for n/γ pulse shape discrimination using a liquid scintillation detector. IEEE Nuclear Science Symposium and Medical Imaging Conference Record. 2003.

  19. Digital Gamma Neutron Discrimination with Liquid Scintillators. Application Note AN2506. Rev. 3, 09 September 2016. 00117-10-DGT20-ANXX.

  20. X and gamma reference radiation for calibrating dosemeters and dose rate meters and for determining their response as a function of photon energy. ISO 4037.

  21. Reference neutron radiations. ISO 8529.

  22. Moiseev NN, Dydyk AV. Investigation of the scintillation spectrometer-dosimeter of gamma quanta and fast neutrons. ANRI. 2016;4:24-30. (Russian).

  23. Description Spectrometer-dosimeter SDMF-1608. Available from:

  24. Varlamov AV, Varlamov VV, Rudenko DS, Stepanov ME. Atlas of Giant Dipole Resonances. IAEA Nuclear Data Section. Vienna: Wagramerstrasse 5, A-1400. 1999.

  25. McDermott BJ, Blain E, Daskalakis A, et al. Ta(n,γ) cross section and average resonance parameter measurements in the unresolved resonance region from 24 to 1180 keV using a filtered-beam technique. Phys Rev. 2017;96:014607(11).

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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