1. Department of Gastrointestinal Surgery, Harbin Medical University Cancer Hospital, Harbin, Heilongjiang 150000, P.R. China
2. Department of Radiotherapy, Harbin Medical University Cancer Hospital, Harbin, Heilongjiang 150000, P.R. China
3. Department of Statistics, Harbin Medical University, Harbin, Heilongjiang 150000, P.R. China