1. Department of Radiation Oncology and Proton Medical Research Centre, University of Tsukuba, Ibaraki 305-8576, Japan
2. Department of Diagnostic Radiology, Mayo Clinic, 200 First St. SW, Rochester, MN, 55905, USA
3. Department of Radiation Oncology, Cathay General Hospital, Taipei, 106, Taiwan
4. Department of Radiation Oncology, Hitachi General Hospital, Ibaraki, 317-0077, Japan
5. Department of Radiation Therapy, Ibaraki Prefectural Central Hospital, Ibaraki Cancer Center, Ibaraki, 309-1793, Japan