Patterns of local-regional failure after intensity-modulated radiotherapy for nasopharyngeal carcinoma

Objective: To investigate the dosimetric patterns of local-regional failure after intensity-modulated radiotherapy (IMRT) for nasopharyngeal carcinoma (NPC), and to provide a clinical basis for further improvement in the therapeutic effect for NPC. Methods: The patterns of local-regional failure in 364 previously untreated NPC patients without distant metastasis who were admitted to our hospital from December 2007 to April 2012 were analyzed. The failures were classified as 'in-field failure' if V_recur within the 95% isodose curve (V_9.5%) was ≥ 95%, 'marginal failure' if V_9.5% was less than 95% and not less than 20%, or 'out-field failure' if V_9.5% was < 20%. The Kaplan-Meier method was used to calculate survival rates. Results: The median follow-up was 40 months (range 3-84 months). The 3-year local failure-free survival, regional failure-free survival, distant metastasis-free survival, overall survival, and progression-free survival were 94.1%, 95.4%, 86.5%, 90.9%, and 78.7%, respectively. A total of 35 patients experienced local-regional recurrence, and in-field recurrence, marginal recurrence, and out-field failure accounted for 81.1%, 8.1%, and 10.8%, respectively. Conclusions: In-field failures are the main dosimetric patterns of local-regional recurrence after IMRT for NPC, suggesting that radiation resistance of tumor cells is an important reason for local-regional failure. (authors)