A Response Surface Approach to Beam Orientation Optimization in Intensity-Modulated Radiation Therapy Treatment Planning

W e view the beam orientation optimization (BOO) problem in intensity-modulated radiation therapy (IMRT) treatment planning as a global optimization problem with expensive objective function evaluations. We propose a response surface method that, in contrast with other approaches, allows for the generation of problem data only for promising beam orientations as the algorithm progresses. This enables the consideration of additional degrees of freedom in the treatment delivery, i.e., many more candidate beam orientations than is possible with existing approaches to BOO. This ability allows us to include noncoplanar beams and consider the question of whether or not noncoplanar beams can provide significant improvement in treatment plan quality. We also show empirically that using our approach, we can generate clinically acceptable treatment plans that require fewer beams than are used in current practice.