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

• Published in: Journal of X-ray science and technology Vol. 26; no. 2; pp. 281 - 302
• Main Authors: Asadi, Amin, Razavi-Ratki, Seid Kazem, Jabbari, Keyvan, Najafzadeh, Milad, Nickfarjam, Abolfazl
• Format: Journal Article
• Language: English
• Published: London, England SAGE Publications 01.01.2018
• Subjects: BEAMnrc; Radiation therapy; Monte Carlo calculations; Monte Carlo code; medical linear accelerator; flattening filter
• ISSN: 0895-3996; 1095-9114
• DOI: 10.3233/XST-17315

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.