1. Department of Radiation Oncology, School of Medicine, Kyung Hee University Hospital at Gangdong, Seoul, Korea.
2. Department of Radiation Oncology, School of Medicine, Kyung Hee University Hospital, Seoul, Korea.
3. Research Institute of Radiological & Medical Science, Korea Institute of Radiological Medical Sciences, Seoul, Korea.
4. Department of Radiation Oncology, Inha University Hospital, Incheon, Korea.