Analysis of Clinical Target Volume Delineation in Local-regional Failure of Nasopharyngeal Carcinoma after Intensity-modulated Radiotherapy

OBJECTIVE: To analyze the pattern of local failure in patients with nasopharyngeal carcinoma (NPC) after intensity-modulated radiotherapy (IMRT) and find a more reasonable delineation of the clinical target volume (CTV). METHODS AND MATERIALS: A total of 212 patients with non-metastatic NPC who underwent IMRT were analyzed. Radiation therapy was run at a total dose of 66-74 Gy (2.0-2.2 Gy fractions). The follow-up of local recurrence and the recurrence-related features were analyzed for the original treatment situation. The failures were delimited as "in-field failure" if V-recur within the 95% isodose curve (V95%) was >= 9.5%; "marginal failure" if V95% was less than 95% and not less than 20%; or "out-field failure" if V95% was< 20%. Kaplan-Meier method was used to calculate the survival rates. RESULTS: The median follow-up was 43.4 months. The 5-year local relapse-free survival and overall survival rates were 85.6 and 77.8%, respectively. A total of 18 patients have relapsed. The in-field failure, marginal failure, and out-field failure accounted for 83.3%, 11.1%, and 5.6%, respectively. The site of recurrence was basically in the high dose area. CONCLUSION: These findings suggested that IMRT provide a good local control for patients with NPC, and the in-field failure is the main mode. A wide range of CTV cannot prevent the local recurrence, narrowing the CTV to protect the adjacent organs should be taken into consideration.