title: Minimizing the uncertainties regarding the effects of delaying radiotherapy for Glioblastoma: A systematic review and meta-analysis.
abstract: OBJECTIVE
  Previous studies have provided no clear conclusions regarding the effects of delaying radiotherapy (RT) in GBM patients. We present a systematic review and meta-analysis to address the effect of delayed RT on the overall survival (OS) of GBM patients.
  
  
  METHODS
  A systematic search retrieved 19 retrospective studies published between 1975 and 2014 reporting on the waiting time (WT) to RT for GBM patients. The meta-analysis was performed by converting WT to RT studies intervals into a regression coefficient (β) and standard error expressing the effect size on OS per week of delay.
  
  
  RESULTS
  Data required to calculate the effect size on OS per week of delay were available for 12 studies (5212 patients). A non-adjusted model and a meta-regression model based on well-recognized prognostic factors were performed. No association between WT to RT, per week of delay, and OS was found (HR=0.98; 95% CI 0.90-1.08; p=0.70). The meta-regression adjusted for prognostic factors weighted by the inverse-variance (1/SE(2)) showed no clear evidence of the effect of WT to RT, per week of delay, on OS.
  
  
  CONCLUSIONS
  This meta-analysis, despite limitations, provided no evidence of a true effect on OS by delaying RT in GBM patients.
authors.affiliation: Hospital Israelita Albert Einstein, São Paulo, Brazil; Universidade Federal de São Paulo (UNIFESP) - Escola Paulista de Medicina - Pós-graduação de Neurologia e Neurociências, São Paulo, Brazil. Electronic address: lvmaia@gmail.com.
authors.forename: Luiz Victor Maia
authors.initials: LV
authors.lastname: Loureiro
authors.affiliation: Hospital Israelita Albert Einstein, São Paulo, Brazil.
authors.forename: Elivane da Silva
authors.initials: Eda S
authors.lastname: Victor
authors.affiliation: Hospital Israelita Albert Einstein, São Paulo, Brazil.
authors.forename: Donato
authors.initials: D
authors.lastname: Callegaro-Filho
authors.affiliation: Hospital Israelita Albert Einstein, São Paulo, Brazil.
authors.forename: Ludmila de Oliveira
authors.initials: Lde O
authors.lastname: Koch
authors.affiliation: Hcor Hospital do Coração Oncologia, São Paulo, Brazil.
authors.forename: Lucíola de Barros
authors.initials: Lde B
authors.lastname: Pontes
authors.affiliation: Hospital Israelita Albert Einstein, São Paulo, Brazil; Faculdade de Medicina da Universidade de São Paulo, Brazil.
authors.forename: Eduardo
authors.initials: E
authors.lastname: Weltman
authors.affiliation: Hospital Israelita Albert Einstein, São Paulo, Brazil.
authors.forename: Edna Terezinha
authors.initials: ET
authors.lastname: Rother
authors.affiliation: Hospital Israelita Albert Einstein, São Paulo, Brazil; Universidade Federal de São Paulo (UNIFESP) - Escola Paulista de Medicina - Pós-graduação de Neurologia e Neurociências, São Paulo, Brazil.
authors.forename: Suzana Maria Fleury
authors.initials: SM
authors.lastname: Malheiros
mesh_terms: D001932:Brain Neoplasms / Q000532:radiotherapy*; D005909:Glioblastoma / Q000532:radiotherapy*; D006801:Humans; D012189:Retrospective Studies; D016019:Survival Analysis; D013995:Time; D035501:Uncertainty
keywords: Delay; Glioblastoma; Prognosis; Radiotherapy; Survival; Waiting time