Yuzuru Niibe1, Keiichi Jingu2, Hiroshi Onishi3. 1. Department of Radiology, Toho University Omori Medical Center, Tokyo, Japan. Electronic address: yniibe-toho@umin.org. 2. Department of Radiation Oncology, Tohoku University Graduate School of Medicine, Sendai, Japan. 3. Department of Radiology, Yamanashi University School of Medicine, Yamanashi, Japan.