1. Laboratory of Image Science and Technology, School of Computer Science and Engineering, Southeast University, Nanjing, Jiangsu 210096, P. R. China
2. Department of Radiation Oncology, Shandong Cancer Hospital and Institute, Shandong First Medical University and Shandong Academy of Medical Sciences, Jinan, Shandong 250117, P. R. China
3. School of Information Science and Engineering, Shandong University, Jinan, Shandong 250100, P. R. China
4. Laboratory of Image Science and Technology, Southeast University, Nanjing, Jiangsu 210096, P. R. China
5. School of Clinical Medicine, Dali University, Dali, Yunnan 671000, P. R. China
6. Department of Radiation Oncology, Medical College of Wisconsin, Milwaukee, WI 53226, USA