Recurrent Patterns in Patients With Nasopharyngeal Caricinoma and Risks Leading to Inaccurate Delineation in Marginal Failure in the Era of Intensity-Modulated Radiotherapy.

OBJECTIVE: To investigate the failure patterns of recurrent nasopharyngeal carcinoma (NPC), especially to identify the relationship between the recurrent-prone anatomic structures and the tumor regression sites after the introduction of chemotherapy (IC). METHOD: A cohort of 1121 non-metastatic patients with NPC was retrospectively enrolled. The pretreatment and recurrent images of each patient were registered to the planning CT. Tumor regression sites after IC (Vicr) overlapped with recurrent tumor (rGTV) were evaluated for the delineation accuracy and dose sufficiency in marginal failure patients. RESULTS: A total of 126 (11.24%) experienced tumor recurrence. Re-evaluation of 12 patients with local marginal recurrence, their rGTV within Vicr predominantly located at choanae, sphenoidal sinus, and cavernous sinus. The regression sites did not receive the full 70 Gy but over half receiving with 60Gy. CONCLUSION: Analysis from marginal failure that exempts tumor regression sites from GTV or an insufficient prescription dose of less than 70 Gy may contribute to marginal failure.