1. Department of Radiation Oncology, the Fourth Hospital of Hebei Medical University, Shijiazhuang 050011, PR China
2. Department of Thoracic Surgery, National Cancer Center/National Clinical Research Center for Cancer/Cancer Hospital, Chinese Academy of Medical Sciences & Peking Union Medical College, Beijing 100021, PR China
3. Department of Radiation Oncology, Duke University, Durham, NC 27708, USA