1. Department of Oncology, Xianyang Hospital, Yan'an University, Xianyang, Shaanxi 712000, P.R. China
2. Radiation Department, People's Hospital of Ankang City, Ankang, Shaanxi 725000, P.R. China
3. Department of Respiratory Medicine, Longnan Hospital, Daqing, Heilongjiang 163453, P.R. China