The Effect of Inaccuracy of MLC Leaf Position against Dose Distribution on VMAT Delivery Technique using EGSnrc Monte Carlo Simulation

A Monte Carlo simulation on VMAT delivery technique has implemented to investigate the effect of inaccuracy of MLC leaf position between the plan and the actual of MLC leaf position. The study aim to compare the dose distributions between these two parameters. In general, these studies divided into two stages, commissioning of head Linac and simulation of the VMAT delivery technique. At the commissioning stage, Monte Carlo simulation on PDD and dose profile for field size 6 × 6 cm2, 10 × 10 cm2 and 20 × 20 cm2 was validating by experimental data. Commissioning results showed a good agreement between the simulation and experimental data. The 6.4 MeV initial incident electrons were used with an average deviation less than 5% for all field size. In the VMAT delivery technique simulation stage, an analysis of DynaLog file using homemade MATLAB program is used and generated the input files for DOSXYZnrc. One dimension of dose profile analyzed at some point sampling to determine differences in the dose distribution in the cylinder acrylic phantom. DynaLog analysis on the data file showed that the leaf error position is less than 1 mm is 97.1% of the total leaf position and no leaf error position is more than 2 mm. The doses distribution error was discovered less than 2% at isocenter. This study showed there is no significant error on doses distribution due to <1% inaccuracy of MLC leaf position. The Monte Carlo simulation was done using 24.7 billion particles of the phase space history file with a standard deviation of Monte Carlo calculations by 31.66%.