COMPUTERIZED OPTIMIZATION OF MULTIPLE ISOCENTERS IN STEREOTAXIC CONVERGENT-BEAM IRRADIATION

A method for the fully computerized determination and optimization of positions of target points and collimator sizes in convergent beam irr adiation is presented. In conventional interactive trial and error met hods, which are very time consuming, the treatment parameters are chos en according to the operator's experience and improved successively. T his time is reduced significantly by the use of a computerized procedu re. After the definition of target volume and organs at risk in the CT or MR scans, an initial configuration is created automatically. In th e next step the target point positions and collimator diameters are op timized by the program. The aim of the optimization is to find a confi guration for which a prescribed dose at the target surface is approxim ated as close as possible. At the same time dose peaks inside the targ et volume are minimized and organs at risk and tissue surrounding the target are spared. To enhance the speed of the optimization a fast met hod for approximate dose calculation in convergent beam irradiation is used. A possible application of the method for calculating the leaf p ositions when irradiating with a micromultileaf collimator is briefly discussed. The success of the procedure has been demonstrated for seve ral clinical cases with up to six target points.