1. Department of Head and Neck Surgery, Iwate Medical University School of Medicine, 2-1-1 Idaidori, Yahaba 028-3695, Japan
2. Department of Radiology, Iwate Medical University School of Medicine, 2-1-1 Idaidori, Yahaba 028-3695, Japan
3. Department of Radiation Therapy, Southern TOHOKU Proton Therapy Center, 7-172 Yatsuyamada, Koriyama 963-8052, Japan
4. Department of Diagnostic Radiology, Southern TOHOKU General Hospital, 7-115 Yatsuyamada, Koriyama 963-8563, Japan
5. Department of Radiation Therapy, QST Hospital, 4-9-1 Anagawa, Inage-ku, Chiba-shi 263-8555, Japan