Tumor Regression and Patterns of Distant Metastasis of T1-T2 Nasopharyngeal Carcinoma with Intensity-Modulated Radiotherapy

PURPOSE: To study tumor regression and failure patterns in T1-T2 non-metastatic nasopharyngeal carcinoma (NPC) after intensity-modulated radiotherapy (IMRT). METHODS: A retrospective analysis of 139 nasopharyngeal carcinoma patients treated with IMRT between January 2005 and December 2010 in our center was performed. According to the AJCC staging system, all primary lesions were attributed to T1 and T2. The prescription doses were 66 Gy at 30 fractions to gross tumor volume of the nasopharynx and the positive neck nodes, 60 Gy to high-risk clinical target volume and 54 Gy to low-risk clinical target volume. Patients staged III, IV A/B or II (lymph node measured 4 cm or more in diameter) received platinum-based chemotherapy. RESULTS: By the end of radiotherapy, 7.2% (10/139), 23.7% (33/139), and 9.4% (13/139) of patients had residual lesions in the nasopharynx, cervical lymph nodes and retropharyngeal lymph nodes, respectively. The majority of patients had complete remission within 6 months of radiotherapy completion. Five months after IMRT, three patients with residual tumors in the cervical lymph nodes underwent surgery. Among these patients, two patients had positive pathological findings, and one patient had negative findings. With a median follow-up of 59 months, the 5-year overall survival, local control, regional control and distant metastasis-free rates were 87.8%, 96.7%, 94.9% and 89.1%, respectively. Fifteen patients developed distant metastases, representing the primary failure pattern. CONCLUSIONS: Most residual lesions that persisted after IMRT vanished completely in six months. Considering the potential damage to normal structures, clinicians should be cautious when considering the use of boost irradiation after radiotherapy. Distant metastasis was the primary cause of treatment failure, which was significantly higher in N2-3 patients than in N0-1. Additional studies to better understand distant metastases are needed.