1. Proton Therapy Center, National Cancer Center, Goyang, Korea;
2. Department of Radiation Oncology, Korea Cancer Center Hospital, Seoul, Korea;
3. Department of Radiation Oncology, Gyeongsang National University Hospital, Jinju, Korea;
4. Department of Radiation Oncology, Samsung Medical Center, Seoul, Korea;
5. Department of Radiation Oncology, National Medical Center, Seoul, Korea