Proton Therapy Reduces Treatment-Related Toxicities for Patients with Nasopharyngeal Cancer: A Case-Match Control Study of Intensity-Modulated Proton Therapy and Intensity-Modulated Photon Therapy

Purpose The physical properties of proton therapy allow for decreased dose delivery to nontarget structures. The purpose of this study was to determine if this translates into a clinical benefit by comparing acute and chronic morbidity between patients with nasopharyngeal carcinoma who are treated with intensity-modulated proton therapy (IMPT) and those treated with intensity-modulated radiation therapy (IMRT). Materials and Methods Patients receiving IMPT for nasopharyngeal cancer from 2011-13 were matched in a 2:1 IMPT to IMRT ratio. Matching criteria were, in order, T-stage, N-stage, radiation dose, chemotherapy type, World Health Organization classification, sex, and age. Results Ten patients treated with IMPT and 20 matched patients treated with IMRT were included. By the end of treatment, 2 IMPT-treated patients (20%) and 13 IMRT-treated patients (65%) required gastrostomy tube (GT) insertion ( P = .020). Patients receiving IMPT had significantly lower mean doses to the oral cavity , brainstem , whole brain, and mandible . Increased mean dose to the oral cavity was associated with a higher rate of GT placement ( P < .001), but mean dose to the brainstem, whole brain, and mandible was not. Partitioning analysis showed that no patient required GT insertion if the mean oral cavity dose was <26 Gy, but all patients with a mean oral cavity dose > 41.8 Gy required GT insertion. Treatment type (IMPT versus IMRT), induction chemotherapy (yes versus no), mean oral cavity dose, mean brainstem dose, and mean mandible dose were entered into the multivariable model. Only higher mean oral cavity dose remained significantly associated with higher GT rates on multivariable analysis (odds ratio, 1.31 [95% confidence interval, 1.09-1.69] per 1 Gy or Gy (RBE) excess to the oral cavity; P = .003). Conclusion Patients with nasopharyngeal cancer who are treated with IMPT have decreased rates of GT placement, which is likely due, in part, to better dose sparing of the oral cavity.