1. Department of Radiation Oncology, Korea University Ansan Hospital, Ansan, Korea.
2. Department of Radiation Oncology, Yonsei University College of Medicine, Seoul, Korea.
3. Department of Radiation Oncology, Inha University Hospital, Incheon, Korea.
4. Department of Radiation Oncology, Korea University Guro Hospital, Seoul, Korea.
5. Department of Radiation Oncology, Korea University Anam Hospital, Seoul, Korea.