A computer-implemented medical data processing method for supporting positioning a patient for treatment by at least one of radiotherapy or radiosurgery, the method comprising executing, on at least one processor of at least one computer, steps of: a) acquiring, at the at least one processor, planning image data describing a digital planning image of an anatomical body part of the patient and of a reference structure, the reference structure being a device attached to the patient; b) acquiring, at the at least one processor and based on the planning image data, reference structure position data describing a predetermined relative position between the reference structure and the anatomical body part and describing a relative position between the reference structure and a target area which is planned to be positioned at a predetermined reference position, wherein the predetermined reference position is the isocentre of a treatment device usable for treating the patient with the at least one of radiotherapy or radiosurgery; c) acquiring, at the at least one processor, thermal image data describing a digital thermal image of the reference structure; d) acquiring, at the at least one processor, imaging device position data describing a predetermined relative position between the thermal imaging device and the predetermined reference position; e) determining, by the at least one processor and based on the planning image data, planning image pattern data describing an image pattern in the digital planning image assigned to the representation of the reference structure, hereinforth called planning image pattern; f) determining, by the at least one processor and based on the thermal image data, thermal image pattern data describing an image pattern in the digital thermal image assigned to the representation of the reference structure, hereinforth called thermal image pattern g) determining, by the at least one processor and based on the reference structure position data and the imaging device position data and the planning image pattern data and the thermal image pattern data, positional difference data describing a difference between a relative position between the anatomical body part and the target area at the point in time at which reference structure position data was generated on the one hand, and a relative position between the anatomical body part and the predetermined reference position at the point in time at which the thermal image data was generated on the other hand, characterized by acquiring, at the at least one processor, thermal reference data describing a predetermined model of a thermal image appearance of the reference structure; and determining, by the at least one processor and based on the thermal reference data and the planning image data, thermal planning data describing a mapping of the predetermined model onto the digital planning image, wherein the determining of the positional difference data is further based on the thermal planning data. a) acquiring, at the at least one processor, planning image data describing a digital planning image of an anatomical body part of the patient and of a reference structure, the reference structure being a device attached to the patient; b) acquiring, at the at least one processor and based on the planning image data, reference structure position data describing a predetermined relative position between the reference structure and the anatomical body part and describing a relative position between the reference structure and a target area which is planned to be positioned at a predetermined reference position, wherein the predetermined reference position is the isocentre of a treatment device usable for treating the patient with the at least one of radiotherapy or radiosurgery; c) acquiring, at the at least one processor, thermal image data describing a digital thermal image of the reference structure; d) acquiring, at the at least one processor, imaging device position data describing a predetermined relative position between the thermal imaging device and the predetermined reference position; e) determining, by the at least one processor and based on the planning image data, planning image pattern data describing an image pattern in the digital planning image assigned to the representation of the reference structure, hereinforth called planning image pattern; f) determining, by the at least one processor and based on the thermal image data, thermal image pattern data describing an image pattern in the digital thermal image assigned to the representation of the reference structure, hereinforth called thermal image pattern g) determining, by the at least one processor and based on the reference structure position data and the imaging device position data and the planning image pattern data and the thermal image pattern data, positional difference data describing a difference between a relative position between the anatomical body part and the target area at the point in time at which reference structure position data was generated on the one hand, and a relative position between the anatomical body part and the predetermined reference position at the point in time at which the thermal image data was generated on the other hand,