Medical apparatus is described including a fiducial component and a position sensor. The component is recognizable as at least a part of a fiducial when appearing in image data of a patient. The component is attachable to the patient. The sensor is attachable to the component at a predetermined location and orientation on the component or is capable of being positioned adjacent the fiducial component without attachment thereto at a predetermined location and orientation. A storage medium is described containing a program which instructs the computer to recognize a predetermined shape of each of at least one portion of a position sensor as at least a part of a real-world fiducial in image data of a patient. The position sensor is adapted to provide position data. Medical apparatus which includes the position sensor and the storage medium is also described.