SU‐E‐T‐793: Static‐Gantry and Rotational IMRT with Flattening Filter Free versus Flattening Filtered Beams

Abstract

Purpose: The flattening filter free (FFF) photon beams offer high dose rate, greatly speeding up treatment delivery. This work aims to evaluate the impact of FFF beam on treatment planning for both static‐gantry (sIMRT) and rotational IMRT (rIMRT). Methods: Both FFF and flattening filtered (FF) photon beams from a Siemens Artiste machine, calibrated to deliver 1 cGy/MU at dmax with a 10×10 cm, 2</sup> field, were used in our study. Both sIMRT and rIMRT plans were generated with either FFF or FF beams for 10 previously treated cases, using a planning system based on direct aperture optimization algorithm (Panther, Prowess). The plans were compared based on dose‐volume histograms with parameters including dose uniformity for planning target volume (PTV) and equivalent uniform dose for organs at risk (OAR), as well as monitor unit (MU) numbers. Results: In general, the plan qualities for rIMRT plans are equal to or slightly better than those for sIMRT, while the plan quality of a FFF‐beam plan is slightly worse than that for the corresponding FF‐beam plan. The plan quality of a FFF‐beam rIMRT plan is close to that for the FF‐beam sIMRT plan, and the former has slightly worse dose uniformity in PTV but slightly better OAR sparing. Both rotational delivery and the use of FFF‐beam require more MUs, with the latter to more extent. The MU increase can be up to 34% for large PTV and complicated OAR configurations. However, FFF‐beam rIMRT has the advantages of high delivery efficiency with overall treatment time reduced by up to 30%. Conclusions: Plan quality degrade associated with FFF beams can be compromised with rotational IMRT technique. The overall treatment time can be reduced with FFF beams, even though the total MUs are increased. FFF beams are more advantageous for a small sized target or less complicated OAR geometry.