1. Department of Otorhinolaryngology-Head and Neck Surgery, Graduate School, Kyung Hee University, Seoul, Korea;
2. Department of Surgery, St. Vincent’s Hospital, the Catholic University of Korea, School of Medicine, Suwon, Korea;
3. Department of Otorhinolaryngology-Head and Neck Surgery, Samsung Changwon Hospital, Sungkyunkwan University School of Medicine, Changwon, Korea;
4. Department of Preventive Medicine, School of Medicine, Kyung Hee University, Seoul, Korea