Collision avoidance for radiation therapy

A method comprising:

• positioning a patient on a patient couch to a target position based on a predetermined setup configuration of the patient couch and a radiation treatment device;
• acquiring at least one image of a portion of the body of the patient;
• comparing the at least one acquired image with at least one previously acquired or generated reference image;
• based on said comparing, calculating a couch shift;
• shifting the patient couch according to the calculated couch shift;
• using at least one surface scanning system to generate a first outline of at least the patient;
• comparing the first outline with an expected shifted version of a second outline, generated before the first outline, to determine if the patient is at a predetermined treatment position;
• and
• checking that the first outline is within a precomputed clearance zone that will not be occupied by any portion of the radiation treatment device or of an imaging device attached to the radiation treatment device during a radiation treatment for the patient.