2947 - Analysis of VMAT with Dynamic Rotating Collimator Versus Traditional VMAT in High Risk Prostate Cancer Radiation
Presenter(s)
E. Shugard1,2, B. Balmir1, D. L. Saenz1, C. H. Chapman1, Y. D. Mutaf1, and C. B. Hui1; 1Kaiser Permanente, Dublin, CA, 2Siemens Healthineers, Palo Alto, CA
Purpose/Objective(s): To compare the clinical benefit of VMAT with dynamic rotating collimator (VMATDRC) versus static collimator VMAT for high-risk intact prostate patients receiving definitive prostate and pelvic nodal radiation.
Materials/Methods: A retrospective study of 50 patients at a single institution from 2022-2025 who received radiation of 7000 cGy to the prostate and 5040 cGy to the pelvic nodes in 28 fractions. The institutional standard of 3-arc VMAT was compared to 3-arc and 2-arc VMATDRC plans. The VMATDRC plans were planned using rotating collimators with arc dominant planning and only one static AP port. All plans were optimized with a standard optimization objective template to minimize planner variation. Plans were normalized to clinically acceptable coverage of PTV7000 at 98% and PTV5040>95%.
Results: Hotelling’s T2 test showed significant quality metric differences between VMATDRC and VMAT plans. Post-hoc analysis showed both 2 and 3-arc DRC plans outperformed VMAT across most quality metrics. Notably, statistically significant differences were seen in the following parameters: Conformity index was reduced with VMATDRC 3-arc and 2-arc over VMAT with mean reductions of 0.073 and 0.066 respectively. VMATDRC plans were also cooler than VMAT with lower D0.03cc global and bowel differences of 264 (238) cGy, 196 (179) cGy, respectively for 3 and 2 arc plans. OAR sparing was also observed in bladder V3000cGy which was reduced with 3-arc (2-arc) DRC by 4% (3.7%) over VMAT. VMATDRC also showed a reduction in rectum V4000cGy of 3.2% for both 3-arc and 2-arc plans. Small bowel showed a statistically significant but small decrease in V4500cGy in DRC plans of 5.0 (3.9) cc. The largest OAR dose improvement was seen in the mean penile bulb as it was lower by 425 (407) cGy in 3-arc(2-arc) VMATDRC plans. Between the 3-arc and 2-arc VMATDRC plans, quality metrics were clinically very similar although there were small statistically significant differences in the D0.03cc globally and in the bowel and femurs of 25, 16, and 20 cGy respectively.
Conclusion: VMATDRC plans in definitive pelvic nodal radiation outperformed the standard 3-arc VMAT plan. The VMATDRC plans demonstrated statistically significant improvement in conformity and OAR sparing compared to standard 3-arc VMAT plan. Given the clinically minor improvement in the 3-arc VMATDRC over 2-arc DRC plan, the 2-arc VMATDRC plan can be a viable and more efficient alternative to the 3-arc VMAT with better plan quality.