A modular approach to intensity-modulated arc therapy optimization with noncoplanar trajectories.

Area of Science:

• Radiation Oncology
• Medical Physics
• Radiotherapy Planning

Background:

• Volumetric modulated arc therapy (VMAT) combines benefits of arc therapy and intensity-modulated radiotherapy (IMRT).
• Noncoplanar beam angles in VMAT can enhance organ sparing while maintaining short treatment times.
• New treatment machines enable simultaneous couch and gantry motion for noncoplanar VMAT.

Purpose of the Study:

• To develop a reliable optimization method for noncoplanar isocentric arc therapy plan optimization.
• To create a modular solution adaptable to existing beam angle selection and VMAT optimization techniques.
• To demonstrate the efficacy of the proposed method in complex clinical scenarios.

Main Methods:

• A three-step treatment planning process: 1) iterative heuristic for noncoplanar beam direction selection, 2) combinatorial optimization for gantry/couch trajectories, and 3) sliding window VMAT algorithm for plan optimization.
• Treatment time is managed by limiting the trajectory tracing duration.
• The method was tested on challenging lung SBRT and brain tumor cases.

Main Results:

• The noncoplanar VMAT optimization method successfully improved dose conformity, homogeneity, and organ sparing in complex cases.
• Achieved comparable treatment times and trajectory lengths to coplanar VMAT plans.
• Demonstrated the ability to meet planning goals in cases previously unsatisfiable with noncoplanar IMRT.

Conclusions:

• The proposed optimization method provides a reliable approach for noncoplanar isocentric VMAT.
• Noncoplanar VMAT, optimized with this method, offers significant advantages for challenging radiotherapy cases.
• This technique enhances therapeutic ratio by improving target coverage and sparing organs at risk.