Trajectory optimization for dynamic couch rotation during volumetric modulated arc radiotherapy.

Area of Science:

• Radiation Oncology
• Medical Physics
• Computational Imaging

Background:

• Non-coplanar radiation beams are utilized in radiotherapy to minimize dose to organs at risk (OAR) through geometric avoidance.
• Volumetric Modulated Arc Therapy (VMAT) typically employs patient couch rotations for non-coplanar beam arrangements.

Purpose of the Study:

• To present and evaluate a trajectory optimization method for dynamic couch rotation during VMAT (DCR-VMAT).
• To assess the potential for OAR sparing with trajectory-optimized DCR-VMAT plans compared to standard coplanar VMAT.

Main Methods:

• A novel DCR-VMAT technique combining ray tracing with a graph search algorithm (Dijkstra's algorithm) was developed.
• Ray tracing generated cost maps indicating OAR voxel intersection for potential source positions.
• Four clinical cases (partial breast, brain, prostate only, prostate and pelvic nodes) were analyzed.

Main Results:

• Trajectory-optimized DCR-VMAT demonstrated significant OAR dose reduction across all tested cases.
• Partial breast: 53% reduction in mean heart dose.
• Brain: Reduced maximum lens doses (61-77%) and globe doses (37-40%).
• Prostate: 15% reduction in mean bowel dose; reduced V50Gy (9%) and V60Gy (45%) for prostate and pelvic nodes.

Conclusions:

• Trajectory optimization in DCR-VMAT effectively reduces OAR dose compared to conventional coplanar VMAT.
• The developed algorithm shows promise for improving treatment planning and patient outcomes.
• Further research will focus on algorithm refinement and validation in larger patient cohorts.