1. Department of Radiation Oncology, Ansan Hospital, Korea University Medical College, Ansan, Gyeonggi-do, Republic of Korea
2. Department of Radiation Oncology, Korea University Medical College, Seoul, Korea
3. Graduate School of Education, Dongguk University, Seoul, Korea
4. Department of Radiation Oncology, Samsung Medical Center, Sungkyunkwan University School of Medicine, Seoul, Republic of Korea