1. From the Division of Esophageal Surgery, Akita University Hospital, Akita, Japan
2. Department of Thoracic Surgery, Akita University Graduate School of Medicine, Akita, Japan
3. Department of Gastrointestinal Surgery, Japanese Red Cross Akita Hospital, Akita, Japan
4. Department of Health Environmental Science and Public Health, Akita University Graduate School of Medicine, Akita, Japan.