Automating Stereotactic Radiosurgery: Technical Validation of In-House Collimator and Couch Optimization
Abstract
Purpose
A custom optimization engine was developed to determine the optimal collimator and couch angles for single-isocenter, multi-lesion LINAC-based stereotactic radiosurgery (SRS). Herein, we demonstrate technical feasibility of the tool within the Eclipse treatment planning system.
Methods
The user interface was developed in C# for easy implementation with Varian’s Eclipse Scripting API and the optimization algorithms were implemented in Python for optimized numerical libraries and efficient vector computations. The software’s starting point begins with one full arc at a couch angle of 0° and three partial arcs at couch angles of 0°, 45°, and 315°. Each arc spawns a Python process with the initial couch angle, gantry positions, and target contours. For each process, the algorithm generates a range of couch angles centered on the initial couch angle. Then, for each couch angle, the algorithm iterates through all control points and calculates the target contours’ projections on the beam eye’s view (BEV). Next, each collimator angle is applied through a change of basis of the BEV and a cost is calculated from the spacing between metastases along the direction of MLC travel. This process is parallelized to assess multiple couch angles simultaneously. The algorithm returns the couch and collimator angles for the lowest scoring combination, which is then used to generate the beam geometry within Eclipse.
Results
The software performed efficiently, generating valid beam geometry within Eclipse in a short amount of time. The angle optimizations took less than a minute for all arcs, with shorter arcs taking less than 30 seconds.
Conclusion
This technical validation demonstrates feasibility for collimator and couch angle optimization of single-isocenter multi-lesion plans. This is a portion of a fully-automated SRS planning tool currently being developed. Next steps include an IRB-approved clinical validation with comprehensive dosimetric and statistical comparisons and open-sourcing the software.