3020 - Radiotherapy for Esophageal Cancer Using a Novel Volumetric Modulated Arc Therapy with Dynamic Collimator Rotation and Static Angle-Modulated Ports: A Planning Study

Purpose/Objective(s):

Chemoradiotherapy for esophageal cancer is associated with late cardiovascular complications that can negatively impact long-term survival. Minimizing cardiac dose may therefore mitigate these complications and improve long-term outcomes. Recently, a new method that integrates a novel planning and delivery solution incorporating volumetric modulated arc therapy (VMAT) delivery technique with dynamic collimator rotation and static angle–modulated ports (STAMPs), has been introduced (VMATp). This study evaluated the potential benefits of VMATp over VMAT in patients with locally advanced esophageal cancer.

Materials/Methods:

Ten patients with locally advanced esophageal cancer who underwent definitive chemoradiotherapy at our institution were included. GTVp and GTVn were defined as the primary tumor and metastatic lymph nodes, respectively. CTVp included GTVp with a 5-mm margin and a 2-cm cranio-caudal esophageal expansion, and CTVn included GTVn with a 5-mm margin. Elective nodal regions were defined as CTVsub. PTV was defined as each CTV plus 5-mm setup margin. VMATp and VMAT plans were generated for each patient with a prescription dose of 50.4 Gy in 28 fractions. Both techniques utilized three full arcs with bilateral avoidance sectors to suppress low-dose irradiation to the lungs. In the VMAT plans, the collimator angle for all three arcs was fixed at 10° using a jaw-tracking. In the VMATp plans, two arcs were optimized with specific collimator rotations and apertures to target the upper and lower halves of the PTV, respectively. This maximized longitudinal modulation of the multi-leaf collimator to accommodate the elongated PTV of esophageal cancer. The remaining arc in the VMATp plans used a fixed 10° collimator angle. Three to four STAMPs with a balanced weighting approach were distributed across each arc in the VMATp plans and positioned at unique angles to avoid parallel-opposed beam orientations. Dose-volume indices, optimization time, estimated delivery time, monitor units (MU), and modulation complexity score (MCS) were compared using the paired t-test or the Wilcoxon signed-rank test. Statistical significance was set at P <0.05.

Results:

The mean heart dose was significantly lower with VMATp compared to VMAT (mean 23.0 vs. 25.0 Gy, P<0.001), as was spinal cord PRV D0.1cc (40.8 vs. 43.0 Gy, P<0.001). Target coverage was improved with VMATp, demonstrating higher PTV D95% (95.6 vs. 95.1%, P=0.049) and PTV D98% (96.6 vs. 92.4%, P<0.001). Optimization time was significantly shorter with VMATp (180.1 vs. 206.0 s, P=0.012). However, the estimated delivery time was significantly longer (280.2 vs. 193.7 s, P<0.001). MU was significantly higher (1009.1 vs. 536.8, P<0.001), and MCS was significantly lower (0.30 vs. 0.40, P<0.001) with VMATp.

Conclusion:

VMATp achieved significant cardiac dose reduction, improved PTV coverage, and shortened optimization time compared with VMAT, although it resulted in a longer estimated delivery time and increased plan complexity.