1. Juntendo University School of Medicine Department of Radiation Oncology, , 3-1-3, Bunkyo-ku, Tokyo 113-8431 , Japan
2. National Cancer Center Hospital Department of Radiation Oncology, , 5-1-1, Chuo-ku, Tokyo 104-0045 , Japan
3. National Cancer Center Hospital East Department of Musculoskeletal Oncology and Rehabilitation, , 6-5-1, Kashiwa-shi, Chiba 277-8577 , Japan
4. National Cancer Center Hospital Division of Radiation Safety and Quality Assurance, , 5-1-1, Chuo-ku, Tokyo 104-0045 , Japan