A multiobjective gradient-based dose optimization algorithm for external beam conformal radiotherapy

A multiobjective gradient-based algorithm has been developed for the purpos e of dose distribution optimization in external beam conformal radiotherapy . This algorithm is based on the concept of gathering the values of all obj ectives into a single value. The weighting factors of the composite objecti ve values are varied in different steps, allowing the reconstruction of the trade-off surfaces (three or more objectives) or curves (two objectives) w hich define the boundary between the feasible and non-feasible domain regio ns. The analysis of these curves allows the decision-maker to select the so lution that best fits the clinical goals. In contrast to all the other algo rithms, our method provides not a single solution but a sample of solutions representing all possible clinical importance factors (weights) for the ob jectives used. The application of this algorithm to two test cases shows th at a correct selection for the importance factors to multiply the individua l objectives in the global objective value is not trivial and that the loca tion and shape of the boundary region between the feasible and non-feasible solution regions are case dependent. Provided that the individual objectiv e functions are analytically differentiable and that the number of objectiv es is the range of two to three, the computation times are acceptable for c linical use. Furthermore, the optimization for a unique combination of impo rtance factors within the aggregate objective function is performed in less than I min.