Beam Angle Optimization in IMRT using Pattern Search Methods: Initial Mesh-size Considerations

In radiotherapy treatments, the selection of appropriate radiation incidence directions is decisive for the quality of the treatment, both for appropriate tumor coverage and for enhance better organs sparing. However, the beam angle optimization (BAO) problem is still an open problem and, in clinical practice, beam directions continue to be manually selected by the treatment planner in a time-consuming trial and error iterative process. The goal of BAO is to improve the quality of the radiation incidence directions used and, at the same time, release the treatment planner for other tasks. The objective of this paper is to discuss the benefits of using pattern search methods in the optimization of the BAO problem. Pattern search methods are derivative-free optimization methods that require few function value evaluations to progress and converge and have the ability to avoid local entrapment. These two characteristics gathered together make pattern search methods suited to address the BAO problem. Considerations about the initial mesh-size importance and other strategies for a better coverage and exploration of the BAO problem search space will be debated.