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

Abstract

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 ≥95%; "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.

Keywords: Clinical target volume; Delineation; Intensity-modulated radiotherapy; Nasopharyngeal carcinoma.

Figure 1

Kaplan-Meier analysis of overall survival (OS) (A) and local relapse-free survival (LRFS) (B) among patients, stratifed by age (C), gender (D), T stage (E), N stage (F), and AJCC stage (G).