Clinical outcomes of carbon‐ion radiotherapy for patients with locoregionally recurrent nasopharyngeal carcinoma

BACKGROUND: Reirradiation for locoregionally recurrent nasopharyngeal carcinoma (LR‐NPC) after high‐dose radiotherapy (RT) is challenging and usually is associated with poor survival and severe toxicities. Because of its physical and biological advantages over photon‐beam RT, carbon‐ion RT (CIRT) could be a potential treatment option for patients with LR‐NPC. METHODS: Patients with LR‐NPC who underwent salvage therapy using CIRT at the Shanghai Proton and Heavy Ion Center between May 2015 and June 2019 were analyzed. CIRT doses were 50 to 69 gray equivalent (GyE) (2.0‐3.0 GyE per fraction). Overall survival (OS), local control, regional control, distant control, and acute and late toxicities were analyzed. Univariable and multivariable analyses of OS and local control were performed using the Cox regression model. RESULTS: Among the 206 patients included, 139 patients (67.5%) had recurrent American Joint Committee on Cancer stage III or stage IV disease. With a median follow‐up of 22.8 months, the 2‐year OS, local control, regional control, and distant control rates were 83.7%, 58.0%, 87.3%, and 94.7%, respectively. Multivariable analysis revealed that older age (P = .017) was predictive of worse OS, whereas a larger tumor volume (P = .049) and a lower biological equivalent dose (P = .029) were associated with inferior local control. No patient developed an acute toxicity of ≥grade 3 during CIRT. Severe (≥grade 3) late toxicities included temporal lobe necrosis (0.97%), cranial neuropathy (0.49%), hearing loss (1.46%), xerostomia (0.49%), and mucosal necrosis (16.02%) (toxicities were graded using the Radiation Therapy Oncology Group and European Organization for Research and Treatment of Cancer criteria). CONCLUSIONS: Salvage treatment using CIRT is efficacious for patients with LR‐NPC and its toxicities are acceptable. CIRT may improve the survival and toxicity profiles substantially for patients with LR‐NPC compared with the reported results after photon‐based intensity‐modulated RT.