Optimization of importance factors and desired doses in a quadratic dose objective function

The Least Square dose Objective function (LSO) is widely used in radiotherapy optimization. In LSO optimization, usually importance factors are assigned to individual regions of interest (ROI). The relative values of importance factors directly affect results of LSO optimization and thus It is important to find proper importance factors. Here, a method of searching optimum voxel based importance factors is introduced. First, each voxel is assigned with its own importance factor. Then the whole set of importance factors is updated systematically to generate better optimization results. The method was tested in a simplified 3D setup. It is shown by comparison with DVHs and isodose plots that the updating importance factor method has potential of improving optimized dose distribution significantly. In order to improve the method´s computational efficiency, an equivalent computational efficient algorithm is proposed. In the equivalent algorithm, the desired doses in LSO objective function are updated while importance factors are kept fixed. The authors expect to see similar optimized dose distribution improvement from implementation of this equivalent algorithm