1. Department of Radiation Oncology, Pusan National University School of Medicine, Yangsan 50612, Republic of Korea
2. Department of Radiation Oncology, Pusan National University Yangsan Hospital, Yangsan 50612, Republic of Korea
3. Department of Radiation Oncology, Pusan National University Hospital, Busan 49241, Republic of Korea
4. Department of Statistics, Pusan National University, Busan 46241, Republic of Korea