An assembly of devices used primarily in radiation therapy applications, for radiation treatment planning, and during therapy treatment to align and monitor a patient's position relative to the isocenter of a radiation therapy system (e.g., a linear accelerator). It detects electromagnetic signals provided by passive implanted markers (transponders) which have been surgically implanted in or near the target site prior to the treatment. This enables accurate positioning and tracking of all information throughout the treatment phase and helps to ensure reproducible alignment between a target portion of the patient's anatomy and the radiation beams.