A novel optimization framework for VMAT with dynamic gantry couch rotation.

Area of Science:

• Radiation Oncology
• Medical Physics
• Computational Biology

Background:

• Volumetric Modulated Arc Therapy (VMAT) with coplanar arcs is efficient but often dosimetrically inferior to non-coplanar Intensity Modulated Radiation Therapy (IMRT).
• Achieving both high dosimetric quality and efficient delivery in VMAT remains a challenge.

Purpose of the Study:

• To develop and evaluate a novel integrated optimization method for non-coplanar VMAT (4πVMAT).
• To assess the dosimetric benefits and delivery feasibility of 4πVMAT compared to coplanar VMAT (2πVMAT).

Main Methods:

• Integrated optimization of Direct Aperture Optimization (DAO) and Beam Trajectory Selection (BTS) for 4πVMAT.
• Utilized least square dose fidelity, anisotropic total variation, single segment, and group sparsity objectives.
• Employed Dijkstra's algorithm for continuous gantry/couch trajectories, incorporating collision detection and machine constraints.

Main Results:

• 4πVMAT demonstrated significant reductions in average maximum and mean organ-at-risk doses (9.63% and 3.08% of prescription dose, respectively) compared to 2πVMAT.
• R50 was reduced by 23.0%, and substantial dose reductions were observed for critical organs like the brainstem, major vessels, and proximal bronchus.
• The method proved feasible for clinical application in brain, lung, and prostate cancer patients.

Conclusions:

• The novel 4πVMAT approach enables efficient delivery of non-coplanar arc trajectories.
• 4πVMAT offers significant dosimetric improvements over coplanar VMAT, enhancing treatment efficacy and patient safety.