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

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). 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 -test and validated using receiver operating characteristic curves. The risk factors of OS were calculated by Cox regression methods. 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. 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.