Abstract: A system for ensuring precision in medical treatment of a patient comprising one or more clusters of targets attached to a patient, a strapping mechanism or a carrier defining a patient-fixed coordinate system. The system also includes a first electro-optical measurement system for observing the one or more clusters of targets and local reference markers of an imaging system to determine the relationship between the patient-fixed coordinate system and a coordinate system of the imaging system, whereby a location to be treated inside the patient can be calculated in the patient-fixed coordinate system. The system further includes a second electro-optical measurement system for observing the one or more clusters of targets and local reference markers of a treatment system, whereby the location to be treated inside the patient can be calculated in a coordinate system of a treatment system.