1. Department of Surgery, Soonchunhyang University Seoul Hospital, Seoul, Korea.
2. Department of Surgery, Daerim St. Mary's Hospital, Seoul, Korea.
3. Department of Surgery, Seoul National University Bundang Hospital, Seoul National University College of Medicine, Seongnam, Korea.
4. Department of Biostatistics, Soonchunhyang University College of Medical Sciences, Seoul, Korea.
5. Department of Surgery, Soonchunhyang University Bucheon Hospital, Bucheon, Korea.