Leaf trajectory calculation for dynamic multileaf collimation to realize optimized fluence profiles

Abstract

An algorithm for the calculation of the required leaf trajectories to generate optimized intensity modulated beam profiles by means of dynamic multileaf collimation is presented. This algorithm iteratively accounts for leaf transmission and collimator scatter and fully avoids tongue-and-groove underdosage effects. Tests on a large number of intensity modulated fields show that only a limited number of iterations, generally less than 10, are necessary to minimize the differences between optimized and realized fluence profiles. To assess the accuracy of the algorithm in combination with the dose calculation algorithm of the Cadplan 3D treatment planning system, predicted absolute dose distributions for optimized fluence profiles were compared with dose distributions measured on the MM50 Racetrack Microtron and resulting from the calculated leaf trajectories. Both theoretical and clinical cases yield an agreement within 2%, or within 2 mm in regions with a high dose gradient, showing that the accuracy is adequate for clinical application.

Mathematical optimization in intensity modulated radiation therapy

“…Another refinement of the algorithm of Van Santvoort and Heijmen (1996) is given by Dirkx et al (1998), which calculates the leaf trajectories considering transmission and collimator scatter and still avoiding tongue-and-groove underdosage effects. The algorithm proposed by Dirkx et al (1998) is in a way a combination of the algorithms of Van Santvoort and Heijmen (1996) and Stein et al (1994).…”

“…The algorithm proposed by Dirkx et al (1998) is in a way a combination of the algorithms of Van Santvoort and Heijmen (1996) and Stein et al (1994). It takes first the desired intensity profile as an input and, at each iteration, calculates the leaf trajectories using the method described by Van Santvoort and Heijmen (1996).…”

Mathematical optimization in intensity modulated radiation therapy

“…Another refinement of the algorithm of Van Santvoort and Heijmen (1996) is given by Dirkx et al (1998), which calculates the leaf trajectories considering transmission and collimator scatter and still avoiding tongue-and-groove underdosage effects. The algorithm proposed by Dirkx et al (1998) is in a way a combination of the algorithms of Van Santvoort and Heijmen (1996) and Stein et al (1994).…”

Energy-and Intensity-Modulated Electron Beam for Breast Cancer Treatment

“…For example, the 'tongue-and-groove' effect may become a significant issue when underdosage occurs between two adjacent leaf pairs due to the fact that the region in between is always covered by the tongue, or the groove or both , Wang et al 1996. Algorithms have therefore been developed to either minimize or remove this effect when MLC leaf sequences are generated , Webb etal 1997, Dirkx et al 1998. There are also some other important factors associated with the use of an MLC, which include the variation of the accelerator head scatter component in the MLC-collimated beam (Brahme 1988, Convery and, the amount of photon leakage through the leaves (Wang et al 1996, Webb 1997, and the effect of back-scattered photons from the moving jaws and MLC leaves on the monitor chamber signal .…”