Fiducial-Less Respiration Tracking in Radiosurgery

Respiratory motion is difficult to compensate for with conventional radiotherapy systems. An accurate tracking method for following the motion of the tumor is of considerable clinical relevance. We investigate methods to compensate for respiratory motion using robotic radiosurgery. Infrared emitters are used to record the motion of the patient's skin surface. The position of internal gold fiducials is computed repeatedly during treatment, via x-ray image processing. We correlate the motion between external and internal markers. From this correlation model we infer the placement of the internal target. 15 patients with lung tumors have recently been treated with a fully integrated system implementing this new method. In this work we extend our method to tracking without implanted fiducials. We propose to use deformation algorithms on CT data sets combined with registration of digitally reconstructed radiographs to obtain intermittent information on the target location. This information is then combined with our basic correlation method to achieve real-time tracking. The term 7D registration is coined to describe the underlying method for performing this task.