LEAF TRAJECTORY CALCULATION FOR DYNAMIC MULTILEAF COLLIMATION TO REALIZE OPTIMIZED FLUENCE PROFILES

An algorithm for the calculation of the required leaf trajectories to generate optimized intensity modulated beam profiles by means of dynam ic multileaf collimation is presented. This algorithm iteratively acco unts for leaf transmission and collimator scatter and fully avoids ton gue-and-groove underdosage effects. Tests on a large number of intensi ty modulated fields show that only a limited number of iterations, gen erally less than 10, are necessary to minimize the differences between optimized and realized fluence profiles. To assess the accuracy of th e algorithm in combination with the dose calculation algorithm of the Cadplan 3D treatment planning system, predicted absolute dose distribu tions for optimized fluence profiles were compared with dose distribut ions measured on the MM50 Racetrack Microtron and resulting from the c alculated leaf trajectories. Both theoretical and clinical cases yield an agreement within 2%, or within 2 mm in regions with a high dose gr adient, showing that the accuracy is adequate for clinical application .