Radiation therapy can be used to treat localized cancer.  In a typical application, a radiation delivery system has an ionizing radiation device mounted to a movable gantry.  The radiation delivery system controls the motion of the radiation device to direct an ionizing radiation beam to a specific point in space commonly referred to as the “machine isocenter.”  One aspect of radiation therapy is positioning a patient so that the patient's tumor is located at the machine isocenter throughout treatment.  Patient positioning systems use various technologies to locate the tumor, including optically locating visual markers applied to the patient's skin, or using X-ray analysis to locate metal fiducials subcutaneously implanted in the patient. 
It is typical for attendants such as radiation therapists to perform tasks relating to radiation treatment, such as positioning the patient for treatment, setting up aspects of the patient positioning system, and monitoring the output of the patient positioning system to ensure that the patient remains properly positioned throughout treatment. 
A patient positioning system that provided information likely to assist the attendants in their tasks in a manner that is clear and easy to understand would have significant utility.