Purpose: To synthesize the direct clinical evidence relating waiting times (WTs) for radiotherapy (RT) to the outcomes of RT.
Methods and materials: 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.