1. Department of Head and Neck Surgery, National Cancer Center Hospital East , Kashiwa , Japan
2. Department of Otorhinolaryngology and Head and Neck Surgery, University of Tokyo Hospital , Tokyo , Japan
3. Department of Head and Neck Surgery , Tokyo Medical and Dental University Medical Hospital, Tokyo , Japan
4. Department of Head and Neck Surgery, Saitama Cancer Center Hospital , Ina , Japan
5. Department of Head and Neck Surgery, Shizuoka Cancer Center Hospital , Nagaizumi , Japan
6. Department of Head and Neck Surgery , Mishima Central Hospital, Mishima , Japan
7. Department of Otorhinolaryngology and Head and Neck Surgery, University of Nagoya Hospital , Nagoya , Japan
8. Department of Otorhinolaryngology and Head and Neck Surgery , Aichi Medical University Hospital, Nagakute , Japan
9. Department of Head and Neck Surgery, The Cancer Institute Hospital of the Japanese Foundation for Cancer Research , Tokyo , Japan
10. Department of Head and Neck Surgery, Miyagi Cancer Center Hospital , Natori , Japan
11. Department of Head and Neck Surgery , National Cancer Center Hospital East, Kashiwa , Japan
12. Department of Head and Neck Surgery, Oosaka International Cancer Institute , Osaka , Japan