Feasibility of dynamic flat beam technique in flattening filter free beam only LINAC - comparison of dynamic flat beam characteristics with standard 6MV flat beam

In recent years application of flattening filter free beam (FFF) has increased tremendously due to its advantages like increased beam intensity, reduced head scatter and out-of-field dose and shorter beam-on time. Due to these advantages, linac vendors are now coming up with FFF beam only (Halycon). The one disadvantage of having only FFF beams is that for conventional 3D radiotherapy of large targets, total body irradiation and other extended SSD treatments such as mantle fields and spinal fields for crano-spinal irradiation, using FFF beams may not be possible. This issue can be addressed by including an internal optimization option to generate a flat beam profile but currently such an option is not available. Therefore in this study from a FFF beam, we try to create a dynamic flattened beam (DFB) using MLC's and IMRT optimization algorithm. Further, we analyze the beam parameters like flatness, symmetry, penumbra, full width at half maximum (FWHM) and cross compare it with standard 6MV flattened beam (F B)