Intensity-modulated carbon-ion radiation therapy versus intensity-modulated photon-based radiation therapy in locally recurrent nasopharyngeal carcinoma: a dosimetric comparison Lei Wang,1–3 Jiyi Hu,2,4 Xiaoli Liu,2,5 Weiwei Wang,2,5 Lin Kong,1,2 Jiade J Lu2,41Department of Radiation Oncology, Shanghai Proton and Heavy Ion Center, Fudan University Cancer Hospital, Shanghai 201315, People’s Republic of China; 2Shanghai Engineering Research Center of Proton and Heavy Ion Radiation Therapy, Shanghai, People’s Republic of China; 3Department of Radiation Oncology, Longhua Hospital, Shanghai University of Traditional Chinese Medicine, Shanghai, People’s Republic of China; 4Department of Radiation Oncology, Shanghai Proton and Heavy Ion Center, Shanghai 201315, People’s Republic of China; 5Department of Medical Physics, Shanghai Proton and Heavy Ion Center, Shanghai 201315, People’s Republic of ChinaCorrespondence: Lin KongDepartment of Radiation Oncology, Shanghai Proton and Heavy Ion Center, Fudan University Cancer Hospital, 4365 Kangxin Road, Pudong, Shanghai 201321, People’s Republic of ChinaEmail lin.kong