Instead of a standard template with pre-drilled holes mounted on the ultrasound support mechanism, the needle positioner device will be attached to the stepper unit. Needles are inserted through the needle positioner, through the perineum and into the prostate, using positions dictated by the dosimetric plan. Ultrasound guidance is used to visualize and guide the needle placement. An optical tracking system (Northern Digital Inc, Waterloo Canada) with measured accuracy of 0.1 millimeter, will be used to track the needle position and angle prior to insertion into tissue.