Abstract: A method and apparatus are provided for irradiating a tumor within a living subject. The method includes the steps of locating the tumor within the living subject, moving a radiation source around the located tumor along a predetermined locus of points having a varying distance between the radiation source and the tumor and steering a radiation beam of the radiation source to irradiate the tumor from each point of the locus of points, where such steering allows the radiation beam to irradiate the tumor at an arbitrary position with respect to the locus of points.