1. Department of Radiation Oncology, Chungbuk National University Hospital, Cheongju 28644, Korea
2. Department of Radiation Oncology, Chungbuk National University Hospital, College of Medicine, Chungbuk National University, Cheongju 28644, Korea
3. Department of Thoracic and Cardiovascular Surgery, Chungbuk National University Hospital, College of Medicine, Chungbuk National University, Cheongju 28644, Korea