The CyberKnife consists of a lightweight linear accelerator mounted on a robotic arm. Near real-time images allow for patient movement tracking within 1mm spatial accuracy. The CyberKnife references the position of the treatment target to internal radiographic features such as the skull, bony landmarks or implanted fiducials rather than a frame. The CyberKnife uses real-time x-rays to establish the position of the lesion during treatment and then dynamically brings the radiation beam into alignment with the observed position of the treatment target. The CyberKnife aims each beam independently. When the target moves, the process detects the change and accommodates it. This treatment system has been used to successfully treat lesions in patients who are otherwise not candidates for surgery or for lesions that are not amenable to open surgical techniques.