Ultra-hypofractionated radiotherapy in early-stage breast cancer — dosimetric comparison between flattening filter (FF) and flattening filter-free (FFF) beams

Introduction. The FAST-Forward trial shows that 26 Gy delivered in 5 fractions over 1 week is non-inferior to the 3-week whole breast irradiation (WBI) regimen. This study compared dynamic tangential volumetric modulated arc therapy (t-VMAT) plans using flattening filter (FF) and flattening filter-free (FFF) beams for ultra-hypofractionated WBI. Material and methods. Treatment plans for 40 early-stage breast cancer patients undergoing deep inspiration breath-hold (DIBH) were analyzed. Parameters included target coverage, organs at risk sparing, homogeneity index (HI), conformity index (CI), beam-on time, monitor units (MUs), dose rate, and gamma passing rate (GPR). Results. For left-sided cases, t-VMAT-FFF significantly reduced maximum doses to the heart and left anterior descending coronary artery and lowered mean dose to the contralateral breast. Beam-on time decreased by 33.7% (left) and 37.1% (right) (p < 0.05). No significant differences were found in target coverage, HI, CI, or GPR. Conclusions. Shortened beam-on time with FFF beams was achieved without compromising target coverage or increasing organ doses, which supports the broader implementation of ultra-hypofractionation.