Dosimetric Comparison between Dynamic Wave Arc and Co-Planar Volumetric Modulated Radiotherapy for Locally Advanced Pancreatic Cancer

Introduction: 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 cases. Material and Methods: DWA and co-VMAT plans were created for ۱۳ patients with LAPC. The prescribed dose was ۴۵.۶ or ۴۸ Gy in ۱۵ fractions. The dose volume indices (DVIs) for target volumes and organs at risk were compared between the corresponding plans. Gamma passing rate, monitor unit (MU), and beam-on time were also compared.  Results: DWA significantly reduced the duodenal V۳۹Gy, V۴۲Gy, and V۴۵Gy by ۱.۱, ۰.۸, and ۰.۲ cm۳, and increased the liver mean dose and D۲cm۳ of the spinal cord planning volume by ۱.۰ and ۱.۵ Gy, respectively. Meanwhile, there was no significant difference in the target volumes except for D۲% of PTV (۱۱۱.۵% in DWA vs. ۱۱۰.۵% in co-VMAT). Further, the gamma passing rate was similar in both plans. MU and beam-on time increased in DWA by ۳۱ MUs and ۱۵ seconds, respectively.  Conclusion: DWA generated significantly lower duodenal doses in LAPC cases, albeit with slight increasing liver and spinal cord doses 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.

Keywords:

Radiotherapy Planning Computer , Assisted Pancreas Cancer Volumetric Modulated Arc Therapy