1. Nagoya City University Graduate School of Medical Sciences Department of Radiology, , Nagoya, 1 Kawasumi, Mizuho-cho, Mizuho-ku, Nagoya, Aichi, 467-8601 , Japan
2. Narita Memorial Proton Center , 78 Shirakawa-cho, Toyohashi, Aichi, 441-8021 , Japan
3. Gunma University Heavy Ion Medical Center , 3-39-22 Showa-machi, Maebashi, Gunma 371-8511 , Japan
4. Nagoya Ekisaikai Hospital Department of Radiology, , 4-66 Syonen-cyo, Nakagawa-ku, Nagoya, Aichi 454-8502 , Japan
5. Aichi Cancer Center Hospital Department of Radiation Oncology, , 1-1 Kanokoden, Chikusaku, Nagoya, Aichi 464-8681 , Japan