1. Department of Oncology, Affiliated Qingdao Central Hospital, Qingdao University, Qingdao, Shandong 266042, P.R. China
2. Department of Respiratory and Critical Care Medicine, The Affiliated People's Hospital of Inner Mongolia Medical University, Hohhot, Inner Mongolia Autonomous Region 010050, P.R. China
3. Department of Geriatrics, The Affiliated People's Hospital of Inner Mongolia Medical University, Hohhot, Inner Mongolia Autonomous Region 010050, P.R. China