1. Department of Surgery II Faculty of Medicine Yamagata University 2‐2‐2 Iida‐Nishi 990‐9585 Yamagata Japan
2. Department of General Thoracic Surgery Yamagata Prefectural Central Hospital 1800, Oazaaoyagi 990‐2292 Yamagata Japan
3. Department of General Thoracic Surgery Higashiyamato Hospital 1‐13‐12 Nangai 207‐0014 Higashiyamato, Tokyo Japan
4. Department of Public Health and Hygiene Yamagata University Graduate School of Medical Science 2‐2‐2 Iida‐Nishi 990‐9585 Yamagata Japan