The Application of Distance Transformation on Parameter Optimization of Inverse Planning in Intensity-Modulated Radiation Therapy (IMRT)

Abstract

In the optimization of inverse planning the parameter specification of the objective function is usually set by either uniform distribution or an arbitrarily defined dose-volume constraint, without spatial information in specific organs. As real dose distributions are essentially non-uniform and mainly determined by shape and location of the involved structures, the spatial information should be utilized to make a parameter specification closer to the perfect one, which is prescribed based on the individual voxel information in treatment planning. However, it is a time-consuming task and might not be feasible in routine treatment planning. In this study, a computer-based method was developed for achieving this goal which produces a non-uniform distribution based on the spatial information of the involved structures in a plan. It consists of two steps: (1) the distance distribution of the involved structures is calculated first using distance transformation technique; (2) the real parameter distribution is generated based on a function designed for converting the distance distribution to the real parameter distribution. The effectiveness of this method was examined for two simulated cases. Their results show that with the application of non-uniform parameter distribution, an evident improvement of dose sparing of the critical organs is achieved without compromising the dose for the target volume and normal tissue.