1. Department of Radiation Oncology, Juntendo University Graduate School of Medicine , 2-1-1 Hongo, Bunkyo-ku, Tokyo 113-8421 , Japan
2. Department of Radiation Oncology, National Cancer Center Hospital , 5-1-1 Tsukiji, Chuo-ku, Tokyo 104-0045 , Japan
3. Department of Radiology, Kyoto Prefectural University of Medicine , 465 Kajii-cho, Kawaramachi-Hirokoji, Kamigyo-ku, Kyoto 602-8566 , Japan
4. National Institutes for Quantum Science and Technology, QST Hospital , 4-9-1 Anagawa, Inage-ku, Chiba 263-8555 , Japan
5. Radiation Safety and Quality Assurance Division, National Cancer Center Hospital , 5-1-1 Tsukiji, Chuo-ku, Tokyo 104-0045 , Japan
6. Department of Radiology, Kansai Medical University Medical Center , 10-15 Fumizono-cho, Moriguchi City, Osaka 570-8507 , Japan
7. Department of Radiation Oncology, Saitama Medical University International Medical Center , 1397-1 Yamane, Hidaka City, Saitama 350-1298 , Japan
8. Department of Radiation Oncology , Proton Medical Research Center, , 2-1-1 Amakubo, Tsukuba, Ibaraki 305-8576 , Japan
9. University of Tsukuba Hospital , Proton Medical Research Center, , 2-1-1 Amakubo, Tsukuba, Ibaraki 305-8576 , Japan
10. Department of Diagnostic Radiology & Radiation Oncology, Chiba University Hospital , 1-8-1 Inohana, Chuo-ku, Chiba-shi, Chiba 260-8677 , Japan
11. Department of Radiation Oncology, Kanagawa Cancer Center , 2-3-2 Nakao, Asahi-ku, Yokohama 241-8515 , Japan
12. Department of Radiation Oncology, Gunma University Graduate School of Medicine , 3-39-22 Showa-machi, Maebashi, Gunma 371-8511 , Japan