ESTIMATION OF NEUTRONS OCCURRING IN THE LINAC ROOM AT DIFFERENT PHOTON ENERGIES

Year 2021, , 160 - 166, 30.12.2021

Taylan Tuğrul

https://doi.org/10.51477/mejs.1007935

Abstract

The high energy photons produced by the Linear accelerator (Linac) induce some nuclear reactions in the materials in the Linac room and Linac head. Neutrons formed as a result of the interaction of photons with materials are called photoneutrons. The aim of the study is to examine the neutron doses formed in the environment for 6 different photon energies. In the study, the components in the Linac head and the Linac chamber are modeled with the help of the Monte Carlo N-Particle (MCNP) program. Then, the flux and dose of photoneutrons formed at 8 different points as a result of 6 different photon energies obtained from the Linac head were measured. as can be seen from the results, as the photon energy used in the Linac increases, the resulting dose and flux of photoneutron increase. It can be understood from results that the amount of neutron dose to be received by the organs in the treatment field may be higher than the other organs. Especially in the treatments where the patient is lying in the prone position, there may be a possibility of neutrons reaching the patient spinal cord. Since photoneutrons with high radiobiological ability may pose a risk of secondary cancer for patients, the photon energy chosen for patient treatments should be chosen appropriately and the use of unnecessary high photon energy should be avoided.

Keywords

Photoneutron, MCNP, Linac, Neutron Flux.

References

• [1] Mesbahi A,Keshtkar A,Mohammadi E,Mohammadzadeh M.Effect of wedge filter and field size on photoneutron dose equivalent for an 18MV photon beam of a medical linear accelerator. Appl.Radiat.Isot. 2010; 68: 84–89.
• [2] Khabaz R, Boodaghi R, Benam MR, Zanganeh V. Estimation of photoneutron dosimetric characteristics in tissues/organs using an improved simple model of linac head. Appl. Radiat. Isot. 2018; 133: 88–94.
• [3] Vega-Carrillo HR, Hernandez-Almaraz B, Hernandez-Da´vila VM, Ortiz-Hernandez A. Neutron spectrum and doses in a 18MV LINAC. J. Radioanal. Nucl. Chem. 2009; 283: 261–265.
• [4] Khabaz R. Effect of each component of a LINAC therapy head on neutron and photon Spectra. Appl. Radiat. Isot. 2018; 139: 40-45.
• [5] Naseri A, Mesbahi A. A review on photoneutrons characteristics in radiation therapy with high-energy photon beams. Rep. Pract. Oncol. Radiother. 2010; 15: 138–144.
• [6] Vega-Carrillo HR, Martı´nez-Ovalle SA, Lallena AM, Mercado GA, Benites- Rengifo JL. Neutron and photon spectra in LINACs. Appl. Radiat. Isot. 2012; 71: 75–80.
• [7] Followill DS, Nüsslin F, Orton CG. IMRT should not be administered at photon energies greater than 10 MV. Med. Phys. 2007; 34: 1877–1879.
• [8] Lin JP, Chu TC, Lin SY, Liu MT. The measurement of photoneutrons in the vicinity of a Siemens Primus linear accelerator. Appl. Radiat. Isot. 2001; 55: 315–321.
• [9] Vega-Carrillo HR, Baltazar-Raigosa A. Photoneutron spectra around an 18 MV LINAC. J. Radioanal. Nucl. Chem. 2011; 287: 323–327.
• [10] Zanini A, Durisi E, Fasolo F, Ongaro C, Visca L, Nastasi U, Burn KW, Scielzo G, Adler JO, Annand JRM, Rosner G. Monte Carlo simulation of the photoneutron field in linac radiotherapy treatments with different collimation systems. Phys. Med. Biol. 2004; 49: 571.
• [11] Benites-Rengifo JL, Vega-Carrillo HR. Neutron Dosimetry in Solid Water Phantom. AIP Conference Proceedings 1626. 2014; 114-116.
• [12] Khaledi N,Dabaghi M,Sardari D,Samiei F,Ahmadabad FG,Jahanfarnia G, Saadi MK,Wang X. Investigation of photoneutron production by Siemens artiste linac: A Monte Carlo Study. Radiation Physics and Chemistry. 2018; 153: 98–103.
• [13] Pena J, Franco L, Gomez F, Iglesias A, Pardo J, Pombar M. Monte Carlo study of Siemens PRIMUS photoneutron production. Phys. Med. Biol. 2005; 50: 5921.
• [14] Sumini M, Isolan L, Cucchi G, Sghedoni R, Iori M. A Monte Carlo model for photoneutron generation by a medical LINAC. Radiation Physics and Chemistry. 2017; 140: 345–348.
• [15] Burn KW, Ongaro C. Photoneutron production and dose evaluation in medical accelerator. Health Phys. Radiat. Eff. 2002; (ENEA-RT-FIS-(2002)(-51).
• [16] d'Errico F, Nath R, Tana L, Curzio G, Alberts WG. In-phantom dosimetry and spectrometry of photoneutrons from an 18 MV linear accelerator. Med. Phys. 1998; 25: 1717–1724.
• [17] Hall EJ, Martin SG, Almols H, Hei TK. Photoneutrons from medical linac accelerators radiobiological measurements and risk estimates. Int.J.Radiat. Oncol. Biol.Phys. 1995; 33: 225–230.
• [18] IAEA, 2000. Handbook on Photonuclear Data for Applications. Cross-Sections and Spectra. International Atomic Energy Agency IAEA-TECDOC-1178, Vienna.
• [19] Martinez-Ovalle SA, Barquero R, Gomez-Ros JM, Lallena AM. Neutron dose equivalent and neutron spectra in tissue for clinical linacs operating at 15, 18 and 20 MV. Radiat. Prot. Dosim. 2011; 147: 498–511.
• [20] Pena J, Franco L, Gomez F, Iglesias A, Pardo J, Pombar M. Monte Carlo study of Siemens PRIMUS photoneutron production. Phys. Med. Biol. 2005; 50: 5921.
• [21] Mohammadi N, Miri-Hakimabad SH, Rafat-Motavalli L. A monte carlo study for photoneutron dose estimation around the high-energy linacs. J. Biomed. Phys. Eng. 2014; 4: 127–139.
• [22] MCNP Version 2.6.0, 2008. MCNPX USER’S MANUAL. Los Alamos National Laboratory, USA.
• [23] Agosteo S, FoglioPara A, Maggioni B. Sangiust V, Terrani S, Borasi G. Radiation transport in a radiotherapy room. Health Phys. 1995; 68: 27–34.
• [24] Carinou E,Kamenopoulou V, Stamatelatos IE. Evaluation of neutron dose in the maze of medical electron accelerators. Med.Phys. 1999; 26: 2520–2525.
• [25] Khabaz R. Analysis of neutron scattering components inside a room with concrete walls. Appl. Radiat. Isot. 2015; 95: 1–7.
• [26] ICRU Report 46, 1992. Photon, Electron, Proton, and Neutron Interaction Data for Body Tissues. International Committee on Radiation Units and Measurements.
• [27] Ghiasi H, Mesbahi A. Monte Carlo characterization of photoneutrons in the radiation therapy with high-energy photons: a comparison between simplified and full Monte Carlo models. Iran. J. Radiat. Res. 2010; 8: 187–193.