Critical analysis of locoregional failures following intensity-modulated radiotherapy for nasopharyngeal carcinoma

Aim: To analyze the patterns of locoregional failure following intensity-modulated radiotherapy (IMRT) for nasopharyngeal carcinoma (NPC) at our institution, as part of an internal quality assurance program. We aimed to investigate the potential existence of a correlation between any part of the IMRT process and clinical outcome. Methods & materials: A total of 106 non-metastatic NPC patients consecutively treated with IMRT (with or without chemotherapy) were analyzed. Radiotherapy was administered using a sequential or simultaneous integrated boost approach at the total prescribed dose of 66-70 Gy (2.00-2.12 Gy per fraction). MRI studies of recurrences were recorded with the planning computed tomography studies to identify volume of failure. Recurrence-related characteristics were analyzed with respect to the original treatment. Failures were classified as 'in-field', 'marginal' or 'out-field' if at least 95, 20-95 or less than 20% of the volume of failure, respectively, was within 95% of the total prescription dose. Results: With a median follow-up of 43.4 months, 5-years local control, regional control, locoregional control and overall survival rates were 87.7, 88.0, 83.5 and 81.3% respectively. A total of 21 failures were registered in 15 patients. In particular, ten failures (47.6%) were classified as 'in-field' (seven local failures and three regional failures [RFs]), nine failures (42.9%) as 'marginal' (five local failures and four RFs) and only two failures (9.5%) as 'out-field' (both RFs). The most relevant causes of failures were suboptimal target definition and target coverage as well as a longer than planned overall treatment time. Conclusion: IMRT determines excellent outcome in NPC patients. However, great attention in all IMRT steps is necessary to reduce potential causes of failure.