Prognostic significance of parapharyngeal extension in nasopharyngeal carcinoma treated with intensity modulated radiotherapy

Abstract

PURPOSE/OBJECTIVE(S): In the era of 2-dimensional conventional radiotherapy, parapharyngeal extension of nasopharyngeal carcinoma (NPC) predicts for higher risk of loco-regional failure and distant metastases. In this study, we evaluate if parapharyngeal extension of NPC i.e., T2b disease in AJCC staging still carries prognostic significance in patients treated with intensity modulated radiotherapy (IMRT). MATERIALS/METHODS: Patients with T1 or T2b, N0 or N1, M0 NPC treated between 2000 to 2005 with IMRT alone were selected for this study. The local control rate, neck node control rate, distant metastases rates, relapse-free survival and overall survival were estimated by Kaplan-Meier method and compared between patients with T1 and T2b disease. RESULTS: Outcomes of 33 patients with T1 disease were compared with 42 patients with T2b disease. For patients with T1 disease, 27 and 6 patients had N0 (81.8%) and N1 (18.2%) disease, respectively. For patients with T2b disease, 15 (35.7%) patients had N0 disease and 27 (64.3%) patients had N1 disease. The dose to gross tumor volume ranged from 68–72 Gy in 34 fractions. Median follow-up was 74 months after completion of IMRT. The 5 years local control rates were 93.8% and 92.9%, respectively, for patients with T1 and T2 disease, neck node control rate were 96.9% and 92.9%, distant metastases rates were 0% and 20.6%, relapse-free survival was 90.6% and 74.9%, and overall survival was 100% and 80.6%, respectively. Local control and neck node control were not affected by T-Stage (p = 0.72 and 0.45, respectively). However, distant metastases rate was significantly higher among patients with T2b disease (p = 0.007) and contributed to poorer 5 years overall survival (p = 0.01). The distant metastases rates of patients with N0 (n = 42) and N1 (n = 33) disease were 4.9% and 18.8%, respectively (p = 0.07). In multivariate analysis testing age, gender, T-Stage and N-Stage, only T-Stage was found to be significant prognostic factor for distant metastases. CONCLUSIONS: With use of IMRT, parapharyngeal extension of NPC is no longer significant for local control but is still important prognostic factor for distant metastases. Parapharyngeal boost is no longer indicated after IMRT but chemotherapy in addition to IMRT should be considered to reduce distant failure.