Feasibility study of using flattening-filter-free photon beams to deliver conventional flat beams

Beam flatness modulation for a flattening filter free photon beam utilizing a novel direct leaf trajectory optimization model

“…From another perspective, if the segment number was restricted extensively for the optimization in order to obtain better delivery efficiency, the flatness generated by the modulated FFF beams would become unacceptable for some cases, especially for those with large field sizes. Compared to step‐and‐shoot delivery, the sliding window technique appears to be a more promising delivery method for keeping both flatness and efficiency to a clinically acceptable level, according to our study . Yet, the currently available SW models fail to incorporate most of the multileaf collimator (MLC) constraints into a global optimization scheme, such as tongue and groove, leaf gap, maximum leaf speed, movable carriage etc .…”

“…Compared to step-and-shoot delivery, the sliding window technique appears to be a more promising delivery method for keeping both flatness and efficiency to a clinically acceptable level, according to our study. 14 Section II.F. Finally, the optimization weighting factors, beam delivery and evaluation methods for the flat beam production are described in Section II.G.…”

“…To the best of our knowledge, no such attempts have been published. However, our previous study provides some insight as to whether or not current IMRT delivery techniques (e.g., step‐and‐shoot, sliding window) are suitable to achieve such a goal . Although the study suggests that reasonably flat dose maps can be achieved in most cases, some practical issues still need to be resolved prior to the full implementation of a FFF‐only machine.…”