Benchmarking of Monte Carlo model of Siemens Oncor^® linear accelerator for 18MV photon beam: Determination of initial electron beam parameters

Article type: Research Article

Authors: Najafzadeh, Milad^a | Hoseini-Ghafarokhi, Mojtaba^b | Bolagh, Rezgar Shahi Mayn^c | Haghparast, Mohammad^a | Zarifi, Shiva^d | Nickfarjam, Abolfazl^e | Farhood, Bagher^{f; *} | Chow, James C.L.^{g; h; *}

Affiliations: [a] Department of Radiology, Faculty of Para-Medicine, Hormozgan University of Medical Sciences, Bandare-Abbas, Iran | [b] Department of Radiology and Nuclear Medicine, School of Para Medical Science, Kermanshah University of Medical Sciences, Kermanshah, Iran | [c] Department of Energy Engineering, Sharif University of Technology, Tehran, Iran | [d] Department of Medical Physics, Faculty of Medicine, Semnan University of Medical Sciences, Semnan, Iran | [e] Department of Medical Physics, Faculty of Medicine, Shahid Sadoughi University of Medical Sciences, Yazd, Iran | [f] Department of Medical Physics and Radiology, Faculty of Paramedical Sciences, Kashan University of Medical Sciences, Kashan, Iran | [g] Department of Radiation Oncology, University of Toronto, Toronto, ON, Canada | [h] Radiation Medicine Program, Princess Margaret Cancer Centre, University Health Network, Toronto, ON, Canada

Correspondence: [*] Corresponding authors: James C.L. Chow, Department of Radiation Oncology, University of Toronto, Toronto, ON, Canada. Tel.: +1 416 946 4501; Fax: +1 416 946 6566; E-mail: james.chow@rmp.uhn.ca and Bagher Farhood, Department of Medical Physics and Radiology, Faculty of Paramedical Sciences, Kashan University of Medical Sciences, Kashan, Iran. E-mail: bffarhood@gmail.com.

Abstract: OBJECTIVE:This study aims to benchmark a Monte Carlo (MC) model of the 18 MV photon beam produced by the Siemens Oncor® linac using the BEAMnrc and DOSXYZnrc codes. METHODS:By matching the percentage depth doses and beam profiles calculated by MC simulations with measurements, the initial electron beam parameters including electron energy, full width at half maximum (spatial FWHM), and mean angular spread were derived for the 10×10 cm2 and 20×20 cm2 field sizes. The MC model of the 18 MV photon beam was then validated against the measurements for different field sizes (5×5, 30×30 and 40×40 cm2) by gamma index analysis. RESULTS:The optimum values for electron energy, spatial FWHM and mean angular spread were 14.2 MeV, 0.08 cm and 0.8 degree, respectively. The MC simulations yielded the comparable measurement results of these optimum parameters. The gamma passing rates (with acceptance criteria of 1% /1 mm) for percentage depth doses were found to be 100% for all field sizes. For cross-line profiles, the gamma passing rates were 100%, 97%, 95%, 96% and 95% for 5×5, 10×10, 20×20, 30×30 and 40×40 cm2 field sizes, respectively. CONCLUSIONS:By validation of the MC model of Siemens Oncor® linac using various field sizes, it was found that both dose profiles of small and large field sizes were very sensitive to the changes in spatial FWHM and mean angular spread of the primary electron beam from the bending magnet. Hence, it is recommended that both small and large field sizes of the 18 MV photon beams should be considered in the Monte Carlo linac modeling.

Keywords: Radiotherapy, Monte Carlo simulation, benchmarking, Siemens Oncor, gamma analysis

DOI: 10.3233/XST-190568

Journal: Journal of X-Ray Science and Technology, vol. 27, no. 6, pp. 1047-1070, 2019