Intra-fraction motion management system and method

A system for monitoring intra-fraction motions of a patient in connection with treatment of treatment volumes such as cancer tumors of said patient in a radiation therapy system, which radiation therapy system comprises an external beam radiation therapy unit having a radiation focus point and a patient positioning unit for positioning a treatment volume in a patient in relation to said focus point in the radiation therapy unit, said system comprising:

• at least one patient marker arranged to be attached to the patient;
• at least one reference marker arranged to positioned in a defined position relative to a patient fixation arrangement for fixation of said patient during treatment;
• an optical tracking system arranged in a position such that images of the patient marker, when said patient marker is provided on the nose of the patient, and the reference markers can be captured;
• and
• a processing module configured to determine a position of the patient marker relative to the coordinate system established by the at least one reference marker based on images captured by the optical tracking system, wherein changes in said position provides information if the patient or a part of said patient has moved relative to said patient fixation arrangement.