Main Session
Sep
29
PQA 05 - Physics
3033 - Optimization of Volumetric Modulated Therapy Including Dynamic Collimator and Static-Angle Modulated Port Configuration for Liver SBRT
Presenter(s)
Mintra Keawsamur, PhD - Chulalongkorn University, Bangkok, Bangkok
M. Keawsamur1, T. Sanghangthum1, S. Kingkaew2, N. Chatchumnan2, N. Amornwichet1, K. Benjangkhaprasert3, K. Thonglert3, J. Suntiruamjairucksa3, C. Chakkabat1, and I. Israngkul Na Ayuthay2; 1Division of Radiation Oncology, Department of Radiology, Faculty of Medicine, Chulalongkorn University, Bangkok, Thailand, 2Division of Radiation Oncology, Department of Radiology, King Chulalongkorn Memorial Hospital, Bangkok, Thailand, 3Division of Radiation Oncology, Department of Radiology, King Chulalongkorn Memorial Hospital, Thai Red Cross Society, Faculty of Medicine, Chulalongkorn University, Bangkok, Thailand
Purpose/Objective(s):
Volumetric arc therapy with integrated dynamic collimator and static angle ports (VMATp) introduces additional geometric degrees of freedom for liver SBRT optimization. However, an optimal angle configuration and the balance of arc-to-static weighting have not yet been established. This study aimed to identify a robust, standardized static angle modulated ports (STAMP) configuration and evaluate the dosimetric impact of weighting to minimize the dose to the normal liver.Materials/Methods:
Twenty liver SBRT cases were stratified by location (left peripheral, right peripheral, and central). The arc angle was fixed from 180° to 60°. Ten predefined STAMP angle configurations were evaluated: four 2-angle combinations [(270°, 210°), (270°, 330°), (0°, 180°), (180°, 60°)], four 3-angle combinations [(300°, 270°, 240°), (315°, 270°, 225°), (330°, 270°, 210°), (0°, 270°, 180°)], and two 4-angle combinations [(0°, 300°, 240°, 180°) and (60°, 340°, 260°, 180°)]. All plans were normalized to ensure that 95% of the PTV received 100% of the prescription dose. Plans had to meet all standard constraints, with the mean liver dose (MLD) serving as the primary dosimetric endpoint and assigned the highest optimization weight after target coverage constraints were met. Plan quality was categorized as Optimal (minimum MLD + =0.5 Gy), Intermediate (minimum MLD + >0.5–1.0 Gy), Suboptimal (minimum MLD + >1.0 Gy or > 10%), or Failed (if any OAR or target metric did not meet acceptable variations). Weighting priorities (arc-dominant -2/-1, balanced 0, static-dominant +1/+2) were analyzed on the highest-performing configuration to assess dosimetric impact.Results:
Optimal classification ranged from 50% to 95%. A four-angle configuration of (0°, 300°, 240°, 180°) demonstrated the highest robustness, achieving 95% Optimal plans with a 0% failure rate. Two-angle and three-angle configurations yielded lower performance, with optimal rates ranging from 50% to 85% and failure rates up to 35%. The four-angle configuration of (0°, 300°, 240°, 180°) yielded the highest optimal rate across all tumor locations. While weight variations had minimal impact on overall dosimetry, balanced weighting (0) yielded 100% Optimal plans. However, static-dominant weighting (+2) improved plan classification in complex, geometrically irregular, or peripherally located targets.Conclusion:
A four-fixed-angle STAMP configuration (0°, 300°, 240°, 180°) provides robust, location-independent performance in liver SBRT. Routine weighting adjustments are generally unnecessary, but static-dominant weighting may provide benefit in complex or peripherally located targets. These findings support protocol standardization, reduced reliance on planners, and the potential automation of VMATp optimization in clinical practice.