Effect of interrupted time during intensity modulated radiation therapy on survival outcomes in patients with nasopharyngeal cancer

Objective: To evaluate the influence of interrupted time (IT) during intensity-modulated radiotherapy (IMRT) on survival outcomes in patients with nasopharyngeal cancer (NPC). Materials and methods: 515 NPC patients receiving IMRT between January 2007 and December 2011 were retrospectively reviewed. The association of IT with locoregional failure-free survival (LRFS), progression free survival (PFS) and overall survival (OS) was assessed by univariate and multivariate analysis. The Kaplan-Meier methodology was used for survival analyses and the differences among groups were assessed by the log-rank test. The Cox model was used for evaluating the prognostic factors for LRFS, PFS, and OS. Results: The 3-year PFS and OS analysis revealed significant difference between patients with a IT >4 days and those with a IT <= 4 days (72.1% vs 81.9%, p < 0.05; 80.8% vs 87.9%, p < 0.05). Age (>= 44 years vs <44 years), T classification, N classification, and IT (>4 days vs <= 4 days) were independent prognostic factors for PFS and OS, respectively (p < 0.05). Only N classification acted as the prognostic factor for LRFS (p < 0.05). Conclusion: The IT of more than 4 days during IMRT may affect survival outcomes of NPC patients. We should minimize the interruption of radiotherapy caused by any reason as much as possible.