1. Department of Minimally Invasive Surgical and Medical Oncology, Fukushima Medical University , 1 Hikarigaoka, Fukushima, Fukushima 960-1295 , Japan
2. Department of Radiology, Southern Tohoku Proton Therapy Center , 7-172 Yatsuyamada, Koriyama, Fukushima 963-8052 , Japan
3. Department of Radiation Oncology , Hyogo Ion Beam Medical Center Kobe Proton Center, 1-6-8 Minatojima-minamimachi, Chuo-ku, Kobe, Hyogo 650-0047 , Japan
4. Department of Radiation Oncology, University of Tsukuba , 1-1-1 Tennoudai, Tsukuba, Ibaraki 305-8575 , Japan
5. Department of Radiation Oncology , Nagoya Proton Therapy Center, , 1-1-1 Hirate-cho, Kita-ku, Nagoya 462-8508 , Japan
6. Nagoya City University West Medical Center , Nagoya Proton Therapy Center, , 1-1-1 Hirate-cho, Kita-ku, Nagoya 462-8508 , Japan
7. Department of Radiation Oncology, Hokkaido University Faculty of Medicine , North-15 West-7, Kita-ku, Sapporo 060-8638 , Japan
8. Department of Radiology, Hyogo Ion Beam Medical Center , 1-2-1 Koto, Shingu-cho, Tatsuno, Hyogo 679-5165 , Japan