title: The relationship between waiting time for radiotherapy and clinical outcomes: a systematic review of the literature.
abstract: OBJECTIVE
  To synthesize the direct clinical evidence relating waiting times (WTs) for radiotherapy (RT) to the outcomes of RT.
  
  
  METHODS
  We did a systematic review of the literature between 1975 and 2005 to identify clinical studies describing the relationship between WTs and outcomes of RT. Only high quality (HQ) studies that had adequately controlled for confounding factors were included in the primary analysis. WTs that had originally been reported as a categorical variable were converted to a continuous variable based on the distribution of WTs in each category. Meta-analyses were done using a fixed-effect model.
  
  
  RESULTS
  The systematic review identified 44 relevant studies. Meta-analyses of 20 HQ studies of local control demonstrated a significant increase in the risk of local failure with increasing WT, RRlocal recurrence/month =1.14, 95% Confidence Intervals (CI): 1.09-1.21. For post-operative RT for breast cancer; RRlocal recurrence/month =1.11, 95%CI: 1.04-1.19. For post-operative RT for head and neck cancer, RRlocal recurrenc/month =1.28, 95%CI: 1.08-1.52. For definitive RT for head and neck cancer, RRlocal recurrence/month =1.15, 95%CI: 1.02-1.29. There was little evidence of any association between WTs and the risk of distant metastasis. Meta-analyses of the 6 HQ studies of breast cancer showed RRmetastasis/month =1.04, 95%CI: 0.98-1.09. Meta-analyses of 4 HQ studies of breast cancer showed no significant decrease in survival with increasing WT, RRdeath/month =1.06, 95%CI: 0.97-1.16, but there was a marginally significant decrease in survival in 4 HQ studies of head and neck cancer, RRdeath/month =1.16, 95%CI: 1.02-1.32.
  
  
  CONCLUSIONS
  The risk of local recurrence increases with increasing WTs for RT. The increase in local recurrence rate may translate into decreased survival in some clinical situations. WTs for RT should be as short as reasonably achievable.
authors.affiliation: Queen's Cancer Research Institute, Queen's University, Kingston, Ontario, Canada.
authors.forename: Zheng
authors.initials: Z
authors.lastname: Chen
authors.forename: Will
authors.initials: W
authors.lastname: King
authors.forename: Robert
authors.initials: R
authors.lastname: Pearcey
authors.forename: Marc
authors.initials: M
authors.lastname: Kerba
authors.forename: William J
authors.initials: WJ
authors.lastname: Mackillop
mesh_terms: D016009:Chi-Square Distribution; D019583:Dose Fractionation, Radiation; D006801:Humans; D009362:Neoplasm Metastasis; D009364:Neoplasm Recurrence, Local; D009369:Neoplasms / Q000473:pathology / Q000532:radiotherapy*; D011878:Radiotherapy; D012307:Risk Factors; D013534:Survival; D013997:Time Factors; D016896:Treatment Outcome; D014850:Waiting Lists