1. Department of Radiation Oncology, Beaumont Health, Proton Beam Therapy Center, Royal Oak, MI, USA;
2. Cancer Center, Union Hospital, Tongji Medical College, Huazhong University of Science and Technology, Wuhan, China;
3. Key Laboratory of Artificial Micro- and Nano-Structures of the Ministry of Education and Center for Electronic Microscopy and Department of Physics, Wuhan University, Wuhan, China