Does Beam Angle Optimization Really Matter for Intensity-Modulated Radiation Therapy?

Abstract

The beam angle optimization (BAO) in intensity-modulated radiation therapy (IMRT) consists on the selection of appropriate radiation incidence directions and can theoretically influence the quality of the IMRT plans, both by improving tumor coverage and by obtaining better organs sparing.However, in clinical practice, the importance of BAO is yet to be acknowledged and, most of the time, beam directions continue to be either equispaced or manually selected by the treatment planner, not making integral part of the optimization loop that is typically devoted to the fluences optimization.During this optimization loop, the treatment planner needs to tune different parameters, in a time consuming process, including, most of the time, objective function weights associated to the different structures included in the optimization procedure. Traditionally, the treatment planning is seen as a sequential process that starts with the selection of the irradiation beam directions.When irradiation beam directions are selected through a BAO procedure that uses the optimal values of the fluence optimization (for a given set of initial objective function weight parameters), does the posterior tuning of the objective function parameters completely jeopardize the BAO effort? The goal of this paper is to contribute to clarify this question, to perceive the importance of BAO in IMRT and its timing within the treatment planning optimization loop. For a study set of ten clinical cases of head-and-neck tumors treated at the Portuguese Institute of Oncology of Coimbra we showed that optimized beam angle sets obtained statistical significant better results ($p-value < 0.001$) than the traditional equispaced configuration. Furthermore, in our tests, despite optimal beam angle sets being always preferable to equispaced configurations, the choice of the weight parameters for angle selection showed influence on the correspondent plan quality.