1. Department of Surgery Institute of Gastroenterology Tokyo Women's Medical University ShinjukuTokyo Japan
2. Department of Biostatistics Graduate School of Medical Science Kyoto Prefectural University of Medicine Kyoto Japan
3. Division of Hepato‐Biliary‐Pancreatic Surgery and Transplantation Kyoto University Graduate School of Medicine Kyoto Japan
4. Division of Hepato‐Biliary‐Pancreatic Surgery and Transplantation Gunma University Graduate School of Medicine Gunma Japan
5. Department of Gastroenterological Surgery I Hokkaido University Graduate School of Medicine Hokkaido Japan
6. Department of Hepato‐Biliary‐Pancreatic and Breast Surgery Ehime University Graduate School of Medicine Ehime Japan
7. Second Department of Surgery Wakayama Medical University Wakayama Japan