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

OBJECTIVES: To evaluate the potential privileges of flattening filter-free (FFF) photon beams from Oncor (R) linac for 6MV and 18MV energies. METHODS: A Monte Carlo (MC) model of Oncor (R) linac was built using BEAMnrc MCCode and verified by the measured data using 6MV and 18MV energies. A comprehensive set of data was also characterized for MC model of Oncor (R) machine running with and without flattening filter (FF) for 6MV and 18MV 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 (R) machine could achieve better treatment results with lower dose toxicity and a shorter beam-on time.