VERIFICATION AND IMPLEMENTATION OF DYNAMIC WEDGE CALCULATIONS IN A TREATMENT PLANNING SYSTEM BASED ON A DOSE-TO-ENERGY-FLUENCE FORMALISM

The use of dynamic movements on linear accelerators during irradiation has found a revised interest lately due to the integration of compute rs to control the accelerator. In this paper, dynamic wedge fields tha t are produced by moving one of the collimator blocks during irradiati on are studied. Since these wedge fields differ from those of mechanic al wedges, certain requirements are to be met on the treatment plannin g system. A pencil-beam-based treatment planning system that uses the resultant energy fluence distribution from the dynamic collimator move ment has been extensively reviewed. In calculations, the system treats the dynamic collimated held as a single, modulated field that yields calculation times close to those for open beams. Details are given on the theoretical model used for the calculation of dynamically generate d dose distributions. Measurements of depth doses, profiles, and outpu t factors in dynamic wedge fields indicate that calculations accuratel y predict the outcome from dynamic wedges without any additional measu rements other than those used for characterization of static open beam s. (C) 1996 American Association of Physicists in Medicine.