A system for ensuring precision in medical treatment of a patient comprising- one or more clusters of targets (11) attached to a patient (2), a strapping mechanism or a carrier (3) defining a patient-fixed coordinate system (2a),- a first electro-optical measurement system for observing the one or more clusters of targets (11) and local reference markers (5) of an imaging system (4) to determine the relationship between the patient-fixed coordinate system (2a) and a coordinate system (5a) of the imaging system (4), whereby a location (1) to be treated inside the patient (2) can be calculated in the patient-fixed coordinate system (2a), and- a second electro-optical measurement system for observing the one or more clusters of targets (11) and local reference markers (9) of a treatment system (8), whereby the location (1) to be treated inside the patient (2) can be calculated in a coordinate system (9a) of a treatment system (8).
