Photon beam dosimetric characteristics of SIEMENS linear accelerator with/without flattening filter

In this study, dosimetric characteristics of percentage depth dose,beam profiles, dose rate on the central axis, and total scattering factor, were estimated by using BEAMnrc and DOSXYZnrc Monte Carlo code, for 6 MV photon beams from a SIEMENS linac with and without flattening filter. The results showed that the percentage depth dose of flattening filter free (FFF) beam were lower than flattening filter (FF) beam; the dose rate on central axis was higher than FF beam, and the ratio of FFF/FF decreased with field size and depth increasing. Besides, the width of penumbra for FFF beam was slightly smaller than that of with FF case. And the variation of total scatter factor showed the flattening filter free mode had smaller depth dependence than flattening filter mode. Our study shows that the beams without flattening can be advantageous in clinical applications. (authors)