Patient fixation. The breast board is tilted by 5° and it has two arm support devices. The patient lies supine with both arms lifted above the head. The RPM marker block is taped to patient skin. The laser lines are aligned to three tattoo marks placed in free breathing on patient skin: two marks on both lateral sides and one on the sternum. There is also one mark on the abdomen to minimize patient rotation. After the laser alignment, translational shifts are performed to the treatment isocenter before the image guidance procedure.