Investigation of micro leaf collimator systems with monte carlo method for 10 MV photon beams with and without flattening filter

In this study, TrueBeam STx linear accelerator and treatment plans which were prepared in Varian Eclipse treatment planning system with AAA and AXB algorithms were simulated using EGSnrc Monte Carlo program. Firstly, open fields and secondly static fields with MLC which were closed more than jaws were evaluated. Test beams were measured with 100 cm source to skin distance (SSD) via Sun Nuclear 3D Scanner water phantom. Gamma analysis with 2% DD and 2 mm DTA were accepted as reference besides field size, penumbra and QI for the evaluation of all PDD and profiles. Unless there is a reasonable explain, all the results were expected to be matched under the gamma analysis. During treatment planning simulation, one large cervix and one small lung 3D conformal plans were evaluated. For the evaluation, MATLAB and CERR software were used. For the comparations of the treatment plans with the simulations, structure specific 3D gamma analysis methods were used as well as DVH graphics. Great match between the simulations and real water phantom measurements were observed. There was good match for 1% DD and 1 mm DTA between AXB and EGSnrc and perfect match for 3% DD and 3 mm DTA. However, it was found that AAA algorithm fails under 1% DD and 1 mm DTA especially on heterogenous environment. In our study, a highly precise Monte Carlo calculation method which is totally independent from any measurement or treatment planning system was developed. It is possible to simulate or verify any situation precisely.