1. Department of Radiation, Fifth People's Hospital of Qinghai Province, Xi Ning, Qing Hai 810007, China
2. Radiologic Sciences and Respiratory Therapy Division, School of Health and Rehabilitation Sciences, The Ohio State University College of Medicine, Columbus, Ohio 43210, USA
3. Interdisciplinary Biophysics Graduate Program, The Ohio State University, Columbus, Ohio 43210, USA
4. Department of Radiation Oncology, Mayo Clinic Arizona, Phoenix, Arizona 85054, USA