Author: Lei Dong, Yin Gao, Taoran Li, Michael Salerno, Boon-Keng Kevin Teo, Melissa Vila 👨🔬
Affiliation: Department of Radiation Oncology, University of Pennsylvania, University of Pennsylvania 🌍
Purpose: A novel solution, RapidArc Dynamic-RAD (Varian Medical Systems, Palo Alto, USA) has been implemented to integrate VMAT with modulation of IMRT-like static-angle ports, including use of a dynamic collimator. This study compared RAD with conventional VMAT and evaluated the performance of different RAD configurations to determine the most optimal approach.
Methods: Plans were created for nine esophageal cancer patients: conventional VMAT with two full arcs, and RAD with 4 static-angle ports (unequally spaced), or 5 and 7 static-angle ports (equidistant), using one full arc and dynamic collimator rotation between modulated ports. Plans used 6 MV, delivering 4500 cGy in 25 fractions normalized to PTV D95%=95%. A two-tailed paired t-test was used to assess differences in DVH metrics between VMAT and RAD plans, and among RAD configurations.
Results: Compared to VMAT plans, lungs V5Gy for RAD plans was significantly reduced while target coverage was maintained. Differences in lungs V20Gy, heart Dmean, D50%, and D20% were not statistically significant. Compared to RAD 4-port plans, the 5-port plans had statistically significant increases in lungs V5Gy and lungs D50%, while differences for the 7-port plan in these metrics were not statistically significant. Differences in lungs V20Gy and heart mean, D50%, and D20% were also not statistically significant. For the 7-port plan, there was a marginal statistically significant decrease in target coverage.
Conclusion: The study demonstrates that RAD significantly reduces low-dose lung exposure compared to VMAT while maintaining comparable target coverage and without significant increases in V20Gy or heart dose. Among RAD configurations, the 4-port offers better low-dose lung sparing compared to the equidistantly spaced 5-port and 7-port plans without compromising target coverage. These findings demonstrate that the 4-port RAD configuration may offer an optimal balance of efficiency and dosimetric benefits, highlighting its potential as an alternative to conventional VMAT for esophageal cancer treatment.