High Superior-Middle Pharyngeal Constrictor Muscle Mean Dose Correlates with Severe Late Lung Infection and Survival in Nasopharyngeal Cancer Patients

PURPOSE: The study aimed to evaluate 1) the correlation of doses of swallowing-related organs at risk (OAR) with severe swallowing-related late adverse effects (AE) in nasopharyngeal carcinoma (NPC) patients and 2) the effect of high mean doses of OARs on overall survival (OS). PATIENTS AND METHODS: This retrospective cohort study enrolled non-metastatic Stage I–IV NPC patients from January 2012 to June 2017. OAR mean doses and severe (≥G3) swallowing-related late AE (xerostomia, dysphagia, and lung infection) were evaluated by t-test and validated using receiver operating characteristic curves. The risk factors of OS were calculated by Cox regression methods. RESULTS: This study enrolled 185 (43 female, 142 male) NPC patients, mean age 52.4 years, primarily with Stage III (93, 50.3%) or Stage IV (67, 36.2%) disease. The mean doses of pharyngeal constrictor muscle (PCM), superior-middle PCM (SMPCM), and superior PCM (SPCM) were significantly higher in those with severe (≥G3) lung infection than in those without (65.7 vs 62.2 Gy, p = 0.036; 68.1 vs 64.2 Gy, p = 0.015; and 70.0 vs 65.9 Gy, p = 0.012, respectively). Patients with severe (≥G3) dysphagia had significant higher mean doses of base of tongue (56.2 vs 50.2 Gy, p = 0.008), laryngeal box (50.6 vs 46.4 Gy, p = 0.036), PCM (65.4 vs 62.1 Gy, p = 0.008), SMPCM (67.1 vs 64.2 Gy, p = 0.014), and SPCM (69.3 vs 65.8 Gy, p = 0.004). Mean SMPCM dose >64.9 Gy (adjusted hazard ratio [aHR] = 3.2, 95% confidence interval [CI] 1.2–8.8, p = 0.021), age >62 years (aHR = 2.7, 95% CI 1.1–6.9, p = 0.032), N3 status (aHR = 4.0, 95% CI 1.8–9.0, p = 001), and severe late AE of lung infection (aHR = 4.6, 95% CI 1.5–14.0, p = 0.007) significantly affected OS. CONCLUSION: Severe lung infection and dysphagia were associated with significantly higher mean doses of PCM, SMPCM, and SPCM. Among these OARs, only a high SMPCM mean dose was a risk factor for OS in NPC patients.