The motion of the couch depends on the motion of the tumor, which in turn depends on the respiration of the patient. However, the couch motion may influence the patient's well being or the patient's respiration. So the question arises: Does the motion of the couch have an influence on the respiration behavior? And also: Does the motion of the couch have an influence on the well being (motion sickness)? And are the well-being and the respiration behavior connected? If the respiration behavior does depend on the couch motion, it may be necessary to control the respiration behavior. Additionally, in the study, the investigators will check an assumption in couch tracking, namely that the patient's body is rigidly fixed to the couch. If this assumption does not hold, the motion of the patient's body relative to the couch will have to be taken into account in couch tracking.