title: Effect of interrupted time during intensity modulated radiation therapy on survival outcomes in patients with nasopharyngeal cancer.
abstract: OBJECTIVE
  To evaluate the influence of interrupted time (IT) during intensity-modulated radiotherapy (IMRT) on survival outcomes in patients with nasopharyngeal cancer (NPC).
  
  
  METHODS
  515 NPC patients receiving IMRT between January 2007 and December 2011 were retrospectively reviewed. The association of IT with loco-regional 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).
  
  
  CONCLUSIONS
  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.
authors.affiliation: Department of Radiation Oncology, Cancer Hospital of Guangxi Medical University, Nanning, People's Republic of China.
authors.forename: Guo-Zeng
authors.initials: GZ
authors.lastname: Xu
authors.affiliation: Department of Radiation Oncology, Cancer Hospital of Guangxi Medical University, Nanning, People's Republic of China.
authors.forename: Ling
authors.initials: L
authors.lastname: Li
authors.affiliation: Department of Radiation Oncology, Cancer Hospital of Guangxi Medical University, Nanning, People's Republic of China.
authors.forename: Xiao-Dong
authors.initials: XD
authors.lastname: Zhu
mesh_terms: D000328:Adult; D002277:Carcinoma / Q000401:mortality / Q000473:pathology / Q000532:radiotherapy*; D018572:Disease-Free Survival; D005260:Female; D006801:Humans; D008297:Male; D000077274:Nasopharyngeal Carcinoma; D009303:Nasopharyngeal Neoplasms / Q000401:mortality / Q000473:pathology / Q000532:radiotherapy*; D009367:Neoplasm Staging; D011379:Prognosis; D050397:Radiotherapy, Intensity-Modulated / Q000379:methods*; D016896:Treatment Outcome
keywords: intensity modulated radiotherapy; interrupted time; nasopharyngeal cancer; prognosis; survival outcomes