1. Tokyo Voice Center, International University of Health and Welfare, Tokyo, Japan;
2. Department of Otolaryngology-Head and Neck Surgery, Jichi Medical University, School of Medicine, Shimotsuke, Japan;
3. Department of Otolaryngology-Head and Neck Surgery, Yamagata University, Faculty of Medicine, Yamagata, Japan;
4. Department of Otolaryngology-Head and Neck Surgery, Tohoku University Graduate School of Medicine, Sendai, Japan;
5. Department of Otolaryngology-Head and Neck Surgery, Tokyo Medical University, Tokyo, Japan;
6. Department of Otolaryngology-Head and Neck Surgery, Toho University Omori Medical Center, Tokyo, Japan;
7. Department of Otolaryngology, Okayama Medical Center, Okayama, Japan;
8. Department of Otolaryngology-Head and Neck Surgery, Hamamatsu University School of Medicine, Hamamatsu, Japan