1. Department of Radiology and Research Institute of Radiology, University of Ulsan College of Medicine, Asan Medical Center, Seoul 138-736, Korea.
2. Department of Diagnostic Radiology, Korea University School of Medicine, Kyungki-do 425-707, Korea.
3. Department of Radiation Oncology, University of Ulsan College of Medicine, Asan Medical Center, Seoul 138-736, Korea.