1. Department of Head and Neck Surgery, National Cancer Center Hospital East, Kashiwa, Japan
2. Department of Head and Neck Surgery, Saitama Cancer Center Hospital, Kitaadachi, Japan
3. Department of Head and Neck Surgery, Oosaka Medical Center for Cancer and Cardiovascular Diseases, Oosaka, Japan
4. Department of Head and Neck Surgery, Aichi Cancer Center Hospital, Nagoya, Japan
5. Department of Otorhinolaryngology and Head and Neck Surgery, University of Tokyo Hospital, Bunkyou, Japan
6. Department of Head and Neck Surgery, Shizuoka Cancer Center Hospital, Sunto, Japan
7. Department of Otorhinolaryngology and Head and Neck Surgery, University of Nagoya Hospital, Nagoya, Japan
8. Department of Head and Neck Surgery, Miyagi Cancer Center Hospital, Natori, Japan
9. Department of Head and Neck Surgery, The Cancer Institute Hospital of Japanese Foundation for Cancer Research, Koutou, Japan