In radiosurgery a moving beam of radiation is used as an ablative surgical instrument to destroy brain tu. roots. Classical radiosurgical systems rely on rigid skeletal fixation of the anatomic region to be treated. This fixation procedure is very pain]ui for the patient and limits radiosurgical procedures to brain lesions. Furthermore, due to the necessity of rigid fixation, radiosurgical treatment with classical systems cannot be fractionated. A new camera-guided system capable of tracking patient motion during treatment has been built to overcome these problems. The radiation source is moved by a six degree-of-freedom robotic arm. In addition to offering a more cost effective, less invasive, and less painful treatment, the robotic gantry allows for arbitrary spatial motion of the radiation source. Based on this feature we can treat non-spherical lesions with accuracies unachievable with classical radiosurgical systems. The system introduces a new class of radiosurgicai procedures, called nonstereotactic, or image-guided radiosurgery. At the heart of these procedures are algorithms for planning both a treatment and the corresponding beam motion, given the geometric description of lesion shapes and relative locations in the particular case.