Correlation of Optical Surface Respiratory Motion Signal and Internal Lung and Liver Tumor Motion: A Retrospective Single-Center Observational Study oleh Guangyu Wang MM, Xinyu Song MM, Guangjun Li MS, Lian Duan BE, Zhibin Li MM, Guyu Dai MM, Long Bai MS, Qing Xiao MM, Xiangbin Zhang MM, Ying Song MS, Sen Bai MS