Optimization of dose distribution for LINAC based radiosurgery using elliptical collimators

The use of non-circular collimators is considered on all or some of the arcs used for radiosurgery on a linear accelerator in order to obtain conformal dose distribution for non-spherical lesions using a single isocenter. An extension of software to allow for use of non-circular collimators and a mathematical optimization based on prescribed doses on the lesion surface and on points in normal tissue (critical structures) are presented. Tests of the optimization method on simulated cases indicate that several boosts from selected positions along the arcs, superimposed on an optimized arc configuration allows one to obtain a highly conformal dose distribution with simple elliptical inserts. The optimization method can be applied to any type of collimation and is particularly effective with variable dose-rate machines.