1. Department of Medical Physics, Shanghai Proton and Heavy Ion Center, Shanghai, China
2. Shanghai key laboratory of radiation oncology (20dz2261000), Shanghai, China
3. Shanghai Engineering Research Center of Proton and Heavy Ion Radiation Therapy, Shanghai, China
4. Department of Radiation Oncology, University of Florida Health Proton Therapy Institute, Jacksonville, FL, USA
5. Department of Radiation Oncology, University Florida, Gainesville, FL, USA