Beam-on-time is an important measure of the delivery efficiency in Intensity-Modulated Radiation Therapy (IMRT). Traditionally, minimizing beam-on-time has been postponed until the Leaf Sequencing stage where the treatment plan quality is already determined and fixed. However, there is a trade-off between the beam-on-time and the treatment plan quality. The aim of this study is to incorporate the beam-on-time into the treatment-plan optimization stage using a Direct Aperture Optimization approach. This will allow for explicitly quantifying that trade-off. In particular, using the special structure of the problem, an exact solution approach is proposed which sequentially characterizes segments of the Pareto-efficient frontier. Furthermore, an approximate solution method, applicable to more classes of treatment plan evaluation criteria, is developed. This solution method is tested on clinical cancer cases and its performance is compared to general approximation techniques available for convex bi-criteria optimization problems.

Co-author: Ehsan Salari, Industrial and Manufacturing Engineering Department, Wichita State University

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