1. Department of Radiology and Radiation Oncology, Kitasato University School of Medicine, 1-15-1 Kitasato, Minami-ku, Kanagawa, Sagamihara 252-0374, Japan
2. Department of Radiation Oncology, Yamanashi University School of Medicine, Yamanashi, Japan
3. Department of Radiation Oncology, Duke University, Durham, NC, USA
4. Department of Radiology, Okayama University Medical School, Okayama, Japan
5. Department of Radiology, The University of Tokyo Hospital, Tokyo, Japan