1. Shenzhen Institute of Advanced Technology, Chinese Academy of Sciences, Shenzhen 518055, China, and Shenzhen College of Advanced Technology, University of Chinese Academy of Sciences, Shenzhen 518055, China.
2. Shenzhen Institute of Advanced Technology, Chinese Academy of Sciences, Shenzhen 518055, China. (e-mail: guopu.zhu@gmail.com)
3. Accuray Inc., Chengdu 610000, China, and was with the Shenzhen Institute of Advanced Technology, Chinese Academy of Sciences, Shenzhen 518055, China.
4. Department of Computer Science, City University of Hong Kong, Hong Kong, and also with the City University of Hong Kong Shenzhen Research Institute, Shenzhen 518000, China.
5. School of Computer Science, Fudan University, Shanghai 200433, China.
6. Department of Computer and Information Science, University of Macau, Macau 999078, China.