A system that generates a three-dimensional model of a tissue surface, for example the inner surface of the heart from two-dimensional image data slices. On this surface, one or more pattern lines are drawn, e.g., by a physician using a user interface, to designate desired lesion(s) on the surface. From the pattern lines, a three-dimensional volume for a lesion can be determined using known constraints. Advantageously, the series of boundaries generated by the three-dimensional volume may be projected back onto the individual CT scans, which then may be transferred to a standard radiosurgical planning tool. A dose cloud may also be projected on the model to aid in evaluating a plan.