Dosimetric benefits of dynamic wave arc over co-planar volumetric modulated radiotherapy for locally advanced pancreatic cancer

Abstract

Background: Dose reduction to the duodenum is important to decrease gastrointestinal toxicities in patients with locally advanced pancreatic cancer (LAPC) treated with definitive radiotherapy. We aimed to investigate whether dynamic wave arc (DWA), a volumetric-modulated beam delivery technique with simultaneous gantry/ring rotations passing the waved trajectories, is superior to coplanar VMAT (co-VMAT) with respect to dose distributions in LAPC. Methods: DWA and co-VMAT plans were created for 13 patients with LAPC in the pancreatic head or body. The prescribed dose was 45.6 or 48 Gy in 15 fractions. The dose volume indices (DVIs) for the gross tumor volume, planning target volume (PTV), stomach, duodenum, small bowel, large bowel, kidney, liver, and spinal cord were compared between the corresponding plans. The values of the gamma passing rate, monitor unit (MU), and beam-on time were also compared. Results: DWA significantly reduced the volumes of the duodenum receiving 39, 42, and 45 Gy by 1.1, 0.8, and 0.2 cm3, respectively. However, the mean liver dose and maximal dose of the spinal cord were increased in DWA by 1.0 and 1.1 Gy, respectively. Meanwhile, there was no significant difference in the target volumes except for dose irradiated to 2% of PTV (PTV D2%) (110.4% in DWA vs. 109.6% in co-VMAT). There were also no significant differences in the other DVIs. Further, the gamma passing rate was similar in both plans. The MU and beam-on time increased in DWA by 31 MUs and 15 seconds, respectively. Conclusion: Compared with co-VMAT, DWA generated significantly lower duodenal doses with acceptable trade-offs in LAPC.