Investigation of Neutron Contamination of Flattening Filter and Flattening Filter-Free 10-MV Photon Beams in Elekta InfinityTM Accelerator

Document Type : Original Paper

Authors

1 Department of Physics, Faculty of Mathematics and Natural Sciences, Institut Teknologi Bandung

2 Department of Radiation Oncology, Concord International Hospital, Singapore/ Singapore

3 National Nuclear Energy Agency

Abstract

Introduction: This study aimed to measure the neutron contamination of flattening filter (FF) and flattening filter-free (FFF) 10-MV photon beams delivered by the Elekta InfinityTM accelerator.
Material and Methods: The photoneutron spectrum produced by the Linac head was evaluated using a Monte Carlo (MC) simulation. The geometry and composition of the head Linac material were modelled based on information obtained from the manufacturer. In this simulation, MC N-Particle Transport Code software (MCNP6) was utilized to model the Linac head and simulate the particle transport. Evaluation of neutron contamination was carried out for the Linac with FF and without it (i.e., FFF). In this regard, the FFF beam was built by removing the FF from the Linac components. The scoring plane, as the neutron spectra calculation area for FF and FFF beams, was placed 99 cm from the target.
Results: The neutron type produced by the head Linac Elekta InfinityTM 10-MV photon mode was mostly thermal and fast. Although there were differences in the neutron intensity of FF and FFF beams, the type of neutrons produced by these two modes had the same energy. Based on the photoneutron reaction energy threshold, it can be concluded that the neutrons produced from the head Linac were the result of photoneutron interactions of high-energy photons with molybdenum-96 and tungsten-184 isotopes.
Conclusion: The photoneutron quantity did not change for FF and FFF beams; however, a larger quantity of neutrons was produced in the FF beam.

Keywords

Main Subjects


  1. References

     

    1. Alem-Bezoubiri A, Bezoubiri F, Badreddine A, Mazrou H, Lounis-Mokrani Z. Monte Carlo estimation of photoneutrons spectra and dose equivalent around an 18 MV medical linear accelerator. Radiation Physics and Chemistry. 2014; 97:381–92.
    2. Mohammadi A, Afarideh H, Davani FA, Ghergherehchi M, Arbabi A.  Monte Carlo study of neutron-ambient dose equivalent to patient in treatment room. Applied Radiation and Isotopes. 2016; 118: 140–8.
    3. Yucel H, Cobanbas I, Kolbas A‚ Yuksel AO, Kaya V. Measurement of photo-neutron dose from an 18-MV medical linac using a foil activation method in view of radiation protection of patients. Nuclear Engineering and Technology. 2016;  48:525–32.
    4. Yani S, Tursinah R, Rhani  MF, Soh RCX, Haryanto F, Arif I. Neutron contamination of Varian Clinac iX 10 MV photon beam using Monte Carlo simulation. Journal of Physics: Conference Series. 2016;  694:012020.
    5. Yani S, Dirgayussa IGE, Rhani MF, Soh RCX, Haryanto F, Arif I. Monte Carlo study on electron contamination and output factors of small field dosimetry in 6 MV photon beam. Smart Science. 2016; 4(2):87-94.
    6. Abou-Taleb WM, Hassan MH, El-Mallah EA, Kotb SM. MCNP5 evaluation of photoneutron production from the Alexandria University 15 MV Elekta Precise medical Linac. Applied Radiation and Isotopes. 2018; 135:184–91.
    7. 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(1):39−43.
    8. Howell RM, Kry SF, Burgett E, Hertel NE, Followill DS. Secondary neutron spectra from modern Varian, Siemens, and Elekta linacs with multileaf collimators. Med. Phys. 2009; 36(9):4027- 38.
    9. Naseri A, Mesbahi A. A review on photoneutrons characteristics in radiation therapy with high-energy photon beams. Reports of Practical Oncology and Radiotherapy. 2010; 15:138–44.
    10. Followill DS, Stovall MS, Kry SF, Ibbott GS. Neutron source strength measurements for Varian, Siemens, Elekta, and General Electric linear accelerators. J Appl Clin Med Phys. 2003; 4:189–94.
    11. Mesbahi A. Dosimetric characteristics of unflattened 6 MV photon beams of a clinical linear accelerator: a Monte Carlo study. Applied Radiation and Isotopes. 2007; 65:1029–36.
    12. Kragl G, af Wetterstedt S, Knäusl B, Lind M, McCavana P, Knöös T, et al. Dosimetric characteristics of 6 and 10MV unflattened photon beams. Radiother Oncol. 2009; 93(1):141-6.
    13. Jank J, Kragl’ G, Georg D. Impact of a flattening filter free linear accelerator on structural shielding design. Z. Med. Phys. 2014; 24:38–48.
    14. Ashokkumar S, Nambira A, Sinha S N, Yadava G, Ramana K, Bhushana M, et al. Measurement and comparison of head scatter factor for 7 MV unflattened (FFF) and 6 MV flattened photon beam using indigenously designed columnar mini phantom. Reports of Practical Oncology and Radiotherapy. 2015; 20:170–80.
    15. Chung JB, Kim JS, Eom KY, Kim IA, Kang SW, Lee JW, et al. Comparison of VMAT-SABR treatment plans with flattening flter (FF) and flattening flter-free (FFF) beam for localized prostate cancer. Journal of Applied Clinical Medical Physics. 2015; 16(6):302–13.
    16. Kry SF, Titt U, Ponisch F, Vassiliev ON, Salehpour M, Gillin M, et al. Energy spectra, sources, and shielding considerations for neutrons generated by a flattening filter-free Clinac. International Journal of Radiation Oncology, Biology, and Physics. 2007; 68:1260–4.
    17. Pichandi A, Ganesh KM, Jerin A, Balaji K, Kilara G. Analysis of physical parameters and determination of inflection point for Flattening Filter Free beams in medical linear accelerator. Reports of Practical Oncology and Radiotherapy. 2014; 19:322–31.
    18. Mesbahi, A. Dosimetric characteristics of unflattened 6 MV photon beams of a clinical linear accelerator: A Monte Carlo study. Applied Radiation and Isotopes. 2007;65:1029–36.
    19. Najem MA, Spyrou NM, Podolyák Z, Abolaban FA. The physical characteristics of the 15 MV Varian Clinac 2100C unflattened beam. Radiation Physics and Chemistry. 2014; 95:205–9.
    20. Wang Y, Khan MK, Ting JY, Easterling SB. Surface Dose Investigation of the Flattening Filter-Free Photon Beams. Int J Radiation Oncol Biol Phys. 2012; 83(2):281-5.
    21. Ezzati AO, Mahdavi SR, Anijdan HM. Size Effects of Gold and Iron Nanoparticles on Radiation Dose Enhancement in Brachytherapy and Teletherapy: A Monte Carlo Study. Iranian Journal of Medical Physics. 2013; 11(2&3):253-9.
    22. Tartar A. Monte Carlo simulation approaches to dose distributions for 6 MV photon beams in clinical linear accelerator. Biocybernetics and Biomedical Engineering. 2014; 34:90–100.
    23. Yani S, Rhani MF, Soh RCX, Haryanto F, Arif I. Monte Carlo simulation of varian clinac iX 10 MV photon beam for small field dosimetry. International Journal of Radiation Research. 2017; 15(3):275-82.
    24. Ghavami SM, Ghiasi H. Estimation of Secondary Skin Cancer Risk Due To Electron Contamination in 18-MV LINAC-Based Prostate Radiotherapy. Iranian Journal of Medical Physics. 2016; 13(4):236-49.
    25. Zolfaghari M, Sedaghatizadeh M. Design and Simulation of Photoneutron Source by MCNPX Monte Carlo Code for Boron Neutron Capture Therapy. Iranian Journal of Medical Physics. 2015; 12(2):129-36.
    26. Sadoughi HR, Nasseri S, Momennezhad M, Sadoghi-Yazdi H, Zare MH, Bahreyni-Toosi MH. Calculations of Linac Photon Dose Distributions in Homogeneous Phantom Using Spline. Iranian Journal of Medical Physics. 2013; 10(3):133-8.
    27. Aghaebrahimian A, Alamatsaz MH. Monte Carlo Evaluation of Gamma Knife Dose Profile in Real Brain Phantom. Iranian Journal of Medical Physics. 2016; 13(1):1-7.
    28. Horová S, Judas L. Monte Carlo modelling of clinical accelerator beams and estimation of primary electron beam parameters. Radioprotection. 2018; 53(1):61–6.
    29. Yani S, Tursinah R, Rhani MF, Haryanto F, Arif I. Comparison between EGSnrc and MCNPX for X-ray target in 6 MV photon beam. Journal of Physics: Conference Series. 2019; 1127: 012014.
    30. Allahverdi M, Zabihzadeh M, Ay MR, Mahdavi SR, Shahriari M, Mesbahi A, et al. Monte Carlo estimation of electron contamination in a 18 MV clinical photon beam. Iran. J. Radiat. Res. 2011; 9(1): 15-28.
    31. Medina AL, Teijeiro A, Garcia J, Esperon J, Terron JA, Ruiz DP, et al. Characterization of electron contamination in megavoltage photon beams. Medical Physics. 2005; 32:1281-92.
    32. Pelowitz DB. MCNPX Users Manual. New Mexico: Los Alamos National Laboratory; 2008.
    33. Allen PD, Chaudhri MA. Photoneutron production in tissue during high energy bremsstrahlung radiotherapy. Physics in Medicine and Biology. 1988; 33:1017–36.