Dosimetric comparison between dynamic wave arc and 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 chemoradiotherapy. We aimed to compare dynamic wave arc (DWA), a volumetric-modulated beam delivery technique with simultaneous gantry/ring rotations passing the waved trajectories, with 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: The volumes of the duodenum receiving 39, 42, and 45 Gy were significantly reduced to 2.8, 0.8 and 0.15 cm3 in DWA from 3.9, 1.6 and 0.34 cm3 in co-VMAT, respectively. The mean dose of the liver and D2cm3 of the planning volume for the spinal cord were significantly increased to 6.9 and 31.7 Gy in DWA from 5.9 and 30.2 Gy in co-VMAT, respectively. Meanwhile, there was no significant difference in the target volumes except for dose irradiated to 2% of PTV (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 96.5% for DWA and 96.7% for co-VMAT (p = 0.65). The MU was significantly higher in DWA than in co-VMAT (620 vs. 589, p = 0.001), and there was a significant increase in the beam-on time (104 sec vs. 89 sec, p = 0.04).Conclusion: DWA was superior to co-VMAT regarding dose distributions in the duodenum in LAPC, albeit with slight increasing doses to the liver and the spinal cord and increasing MU and the beam delivery time. Further evaluation is needed to know how the dose differences would affect the clinical outcomes in chemoradiotherapy for LAPC.