Optimized planning using physical objectives and constraints

Intensity-modulated radiation therapy (IMRT) allows one to achieve a better conformation of the high-dose region to the prescribed tumor target volume than uniform beam therapy, especially in complex treatment situations. Still, perfect conformation is impossible. Hence the goal of optimized IMRT planning or inverse planning is to find the beam profiles that yield the optimum among the physically achievable treatment plans. The principal physical advantage of IMRT is best exploited if the optimization is driven by physical criteria. This article presents an overview of such physical, yet clinically relevant, criteria along with optimization algorithms that take these criteria into account. Practical computer implementations are described, which allow one to perform the optimization in an interactive manner within a few minutes. The application of these methods to some complex clinical example cases is presented, and the results are compared with uniform beam treatment plans and with biologically optimized plans.