A computer-implemented medical data processing method for determining a deviation between a planned and an actual relative position between an anatomical body part of a patient's body and a radiation treatment apparatus, the method comprising executing, on at least one processor of at least one computer, steps of: a) receiving, at the at least one processor, planned control point data describing predetermined control points each describing a predetermined operational state of the radiation treatment apparatus, the control points having a predetermined temporal order in which they are planned to be assumed by the radiation treatment apparatus and each control point being associated with a predetermined planned relative position between the anatomical body part and a monitoring imaging apparatus; b) determining, at the at least one processor, current control point data describing whether the radiation treatment apparatus has assumed a predetermined control point; c) receiving, at the at least one processor, monitoring image data describing at least one digital medical monitoring image of the anatomical body part in at least one monitoring relative position between the anatomical body part and the monitoring imaging apparatus, wherein the monitoring imaging apparatus is used to generate the monitoring image; d) receiving, at the at least one processor, patient image data describing a predetermined medical image of the anatomical body part; e) determining, by the at least one processor and based on the patient image data and the current control point data and the planned control point data, comparison image data describing at least one digital medical comparison image of the anatomical body part in the monitoring relative position; f) determining, by the at least one processor and based on the comparison image data and the monitoring image data, position deviation data describing a positional deviation between the planned relative position associated with the planned control point assumed by the radiation treatment apparatus on the one hand and the monitoring relative position on the other hand, wherein the method comprises g) at least one of the following steps g1) and g2): g1) generating the comparison image data if the current control point data describes that the radiation treatment apparatus has assumed a predetermined control point; or g2) generating the monitoring image data if the current control point data describes that the radiation treatment apparatus has assumed a predetermined control point, wherein the predetermined operational state is defined by at least one of a patient support unit angle, a patient support unit position and a collimator geometry. a) receiving, at the at least one processor, planned control point data describing predetermined control points each describing a predetermined operational state of the radiation treatment apparatus, the control points having a predetermined temporal order in which they are planned to be assumed by the radiation treatment apparatus and each control point being associated with a predetermined planned relative position between the anatomical body part and a monitoring imaging apparatus; b) determining, at the at least one processor, current control point data describing whether the radiation treatment apparatus has assumed a predetermined control point; c) receiving, at the at least one processor, monitoring image data describing at least one digital medical monitoring image of the anatomical body part in at least one monitoring relative position between the anatomical body part and the monitoring imaging apparatus, wherein the monitoring imaging apparatus is used to generate the monitoring image; d) receiving, at the at least one processor, patient image data describing a predetermined medical image of the anatomical body part; e) determining, by the at least one processor and based on the patient image data and the current control point data and the planned control point data, comparison image data describing at least one digital medical comparison image of the anatomical body part in the monitoring relative position; f) determining, by the at least one processor and based on the comparison image data and the monitoring image data, position deviation data describing a positional deviation between the planned relative position associated with the planned control point assumed by the radiation treatment apparatus on the one hand and the monitoring relative position on the other hand, wherein the method comprises g) at least one of the following steps g1) and g2): g1) generating the comparison image data if the current control point data describes that the radiation treatment apparatus has assumed a predetermined control point; or g2) generating the monitoring image data if the current control point data describes that the radiation treatment apparatus has assumed a predetermined control point, g1) generating the comparison image data if the current control point data describes that the radiation treatment apparatus has assumed a predetermined control point; or g2) generating the monitoring image data if the current control point data describes that the radiation treatment apparatus has assumed a predetermined control point,