An optical tracking system may comprise a reference marker unit stationarily disposed relative to a patient, a shape measurement unit configured to measure the three-dimensional shape of a specified part of the patient corresponding to a three-dimensional image, a tracking sensor unit configured to sense the reference marker unit and the shape measurement unit, and a processing unit. The processing unit may acquire a coordinate transformation relationship between the reference marker unit and the tracking sensor unit and a coordinate transformation relationship between the shape measurement unit and the tracking sensor unit based on a sensing result of the tracking sensor unit, acquire a coordinate transformation relationship between the specified part of the patient and the shape measurement unit based on a measurement result of the shape measurement unit, and define a coordinate system of the patient relative to the reference marker unit from the acquired coordinate transformation relationships.
