Monte Carlo evaluation of the potential benefits of flattening filter free beams from the Oncor^® clinical linear accelerator

Article type: Research Article

Authors: Asadi, Amin^a | Razavi-Ratki, Seid Kazem^{b; d} | Jabbari, Keyvan^c | Najafzadeh, Milad^a | Nickfarjam, Abolfazl^{a; b; *}

Affiliations: [a] Medical Physics Department, Faculty of Medicine, Shahid Sadoughi University of Medical Sciences, Yazd, Iran | [b] Radiotherapy Research Center, Shahid Sadoughi University of Medical Sciences, Yazd, Iran | [c] Medical Physics Department, Faculty of Medicine, Isfahan University of Medical Sciences, Isfahan, Iran | [d] Radiology Department, Faculty of Medicine, Shahid Sadoughi University of Medical Sciences, Yazd, Iran

Correspondence: [*] Corresponding author: Abolfazl Nickfarjam, Medical Physics Department, Faculty of Medicine, Shahid Sadoughi University of Medical Sciences, Professor Hesabi Blvd., Alem Sq., Yazd, Iran. Tel.: +98 915 108 9102; Fax: +98 353 821 1222; E-mails: [email protected] and [email protected].

Abstract: OBJECTIVES:To evaluate the potential privileges of flattening filter-free (FFF) photon beams from Oncor® linac for 6 MV and 18 MV energies. METHODS:A Monte Carlo (MC) model of Oncor® linac was built using BEAMnrc MCCode and verified by the measured data using 6 MV and 18 MV energies. A comprehensive set of data was also characterized for MC model of Oncor® machine running with and without flattening filter (FF) for 6 MV and 18 MV beams in six field sizes. The investigated characteristics included mean energy, energy spectrum, photon spatial fluence, superficial dose, percent depth dose (PDD), dose output, and out-of-field dose with two indexes of lateral dose profile and isodose curve at three depths. RESULTS:Using FFF enhanced the energy uniformity 3.4±0.11% (6 MV) and 2.05±0.09% (18 MV) times and improved dose output by factor of 2.91 (6 MV) and 4.2 (18 MV) on the central axis, respectively. Using FFF also reduced the PDD dependencies by 9.1% (6 MV) and 5.57% (18 MV). In addition, using FFF had a lower out-of-field dose due to the reduced head scatter and softer spectra. CONCLUSIONS:The findings in this study suggested that using FFF, Oncor® machine could achieve better treatment results with lower dose toxicity and a shorter beam-on time.

Keywords: Radiation therapy, medical linear accelerator, flattening filter, Monte Carlo calculations, BEAMnrc, Monte Carlo code

DOI: 10.3233/XST-17315

Journal: Journal of X-Ray Science and Technology, vol. 26, no. 2, pp. 281-302, 2018