Delivery of a VMAT technique with flattening filter (FF) and flattening filter free (FFF) mode for whole breast irradiation with five fractions (FAST-Forward trial).

Abstract

To investigate the feasibility of volumetric modulated arc therapy (VMAT) delivery for whole breast irradiation with a 5-fraction regimen according to the FAST-Forward trial. Recently, we treated 10 patients with carcinoma of the left breast after breast conserving surgery. The dose prescription to the PTV was 26 Gy in 5 fractions. Treatment plans were produced using a VMAT technique with the Eclipse treatment planning system for 6 MV flattening filter (FF) and FF free (FFF) beams. Dose volume histograms (DVHs) for the PTV and the organs at risk (OARs), the ipsilateral lung and heart, were compared with the dose constraints specified in the FAST-Forward trial (PTV, D95 > 95%, D5 < 105%, D2 < 107% and Dmax < 110%; ipsilateral lung, D15 < 8Gy; Heart, D30 < 1.5Gy and D5 < 7Gy). Furthermore, conformity index (CI), homogeneity index (HI) and dose to the heart, contralateral lung, contralateral breast, and left anterior descending artery (LAD), were also assessed. Mean ± SD D95(%), D5(%), D2(%), and Dmax (%) for PTV were 97.75 ± 1.12, 105.2 ± 0.82, 105.90 ± 0.89, 109.36 ± 1.00 (FF) and 96.46 ± 0.75, 103.97 ± 0.97, 104.70 ± 1.09, 108.58 ± 1.33 (FFF) respectively. The mean ± SD CI was 1.07 ± 0.05 (FF), 1.048 ± 0.06 (FFF) and HI was 0.11 ± 0.02 (FF), 0.10 ± 0.02 (FFF). Dose constraints for OARs were met for both treatment techniques. However, D15 (Gy) for ipsilateral lung was 3.0% lower with FFF beams. In contrast, D5 (Gy) for heart was 9.0% higher with FFF beams. The dose difference between FF and FFF beams for other OARs such as contralateral lung-D10 (Gy) contralateral breast-D5 (Gy) and LAD was up to 6.0%. Both FF and FFF methods met the acceptable criteria. However, the treatment plans with FFF mode were more conformal and provided greater target homogeneity.