AbstractID: 6841 Title: Intensity-modulated radiosurgery treatment planning by fluence mapping multiisocenter plans The multiple isocenter, weighted arc technique of stereotactic radiosurgery has been shown to produce highly conformal dose distributions with steep dose gradients, but the time required to deliver the treatment to a complex target requiring many isocenters exceeds several hours. In this investigation, a unique method of intensity modulation that approximates the fluence map produced by a multiple-isocenter arc technique is employed. An algorithm was created that reads the dosimetry file from the multiple-isocenter treatment plan, segments each arc into a set of static beams and combines all of the beams from a given direction into a single beam aimed at the target center of mass. The fluence maps used to modulate the intensity of each beamlet were then determined by summing up the contribution of every isocenter to every pixel in each beams-eye view. These fluence maps were then formatted for CADPLAN (Varian Medical Systems) to calculate the mMLC leaf motion and resulting dose distribution to compare with that of the original treatment plan.