Dosimetric comparison of volumetric modulation arc radiotherapy with flattening filter-free beams with IMRT for upper thoracic esophageal cancer

Objective: To compare the dosimetric difference between RapidArc with flattening filter-free Beams (RA-FFF) and static gantry intensity-modulated radiotherapy (IMRT) for upper thoracic esophageal cancer by means of Varian TrueBeam^TM accelerator. Methods: A total of 10 patients with upper thoracic esophageal cancer staged cT_2-3N_0-1M₀ were enrolled. RA-FFF and IMRT treatment plans with radical intent were generated by Varian Eclipse^TM TPS 10.0.4 for each patient. All plans were prescribed 60 Gy in 30 fractions. The RA-FFF plans were compared with IMRT in terms of dosimetric quality and delivery efficiency. Results: Both of the two plans provided similar conformity index, while IMRT had a improved homogeneity index than that of RA-FFF(t = 7.298, P = 0.008). For the lung, the values of V₂₀, V₅ in RA-FFF plan was lower than that of IMRT plan(t = 2.451, 2.604 P < 0.05). The treatment planning time of RA-FFF plans were longer than that of IMRT plans[(5.3 ± 1.4), (3.5 ± 1.7) h, t = 2.585, P < 0.05]. The monitor units for RA-FFF and IMRT were 632 ± 213 and 734 ± 132(t = -1.287, P = 0.084), respectively. The treatment time of RA-FFF and IMRT were 2.2 ± 0.9 and 4.5 ± 1.3, respectively(t = 4.60, P < 0.01). Conclusions: For patients with upper thoracic esophageal cancer, RA-FFF plan, compared with IMRT plan, has a similar target coverage and better dose sparing to the lungs. In addition, RA-FFF plan has fewer MUs, less treatment time and better treatment efficiency. (authors)