ization of stationar

A new approach is suggested for the optimization of stationary and more general moving beam type of irradiations. The method reverses the order of conventional treatment planning as it derives the optimum incident beam dose distributions from the desired dose distribution in the target volume. It is therefore deterministic and largely avoids the trial and error approach often applied in treatment planning of today. Based on the approximate spatial invariance of the convergent beam point irradi.ation dose distribution, the desired dose distribution in the target volume is analyzed in terms of the optimum density of such point irradiations. Since each point irradiation distribution is optimal for the irradiation of a given point and due to the linearity of individual energy depositions or absorbed dose contributions, the resultant point irradiation density will also generate the best possible irradiation of an extended target volume when the maximum absorbed dose at a certain distance from the target should be minimized. The optimum shape of the incident beam for each position of the gantry is obtained simply by inverse back projection of the point irradiation density on the position of the radiation source for that orientation of the incident beam.