A1) Detrimental effects of respiration motion Respiration motion affects all tumor sites in the thorax and abdomen, although the disease of most prevalence and relevance for radiotherapy is lung cancer. Many studies have been performed to study lung-tumor motion and methods to compensate for this motion during radiation treatment imaging, planning and delivery. The significance of the respiration motion compensation techniques is to reduce the mobility of the tumors and thereby reduce the dose to the surrounding normal structures. If no motion compensation methods are used then a margin must be added to ensure adequate coverage of the tumor. Large margins results in radiation delivered to a larger volume of critical structures.