Systems and methods for locating and defining a target location within a human body. The system can include at least one marker, a probe, and a detector for use in locating the markers by providing information to a surgeon that is representative of changes in proximity between the probe and the marker. The marker can have various detection characteristics, e.g., gamma radiation, that are detectable by an associated probe and detector. The tissue volume is removed by manipulating a cutting tool based on the proximity information provided by the detector, which can be used by the surgeon to define the boundary of the tissue volume. The systems and methods of the invention are particularly useful in locating and then removing a tissue volume or other target location from amorphous, pliable tissue (e.g., breast tissue) or other body parts.