Temporal relationship of post-operative radiotherapy with temozolomide and oncologic outcome for glioblastoma.

To determine the impact of delay between surgery and radiotherapy on overall survival (OS) in temozolomide treatmented patients with the incorporation of O6-methylguanine-DNA methyltransferase (MGMT). From 2000 to 2012, 345 consecutive glioblastoma patients were treated with surgery, radiotherapy, and temozolomide at our institution. A Cox-regression model was constructed using significant univariate parameters, known prognostic factors including MGMT, and the interval from surgery to radiotherapy (≤ 2, 2-5, and ≥ 6 weeks). Survival rates were calculated by Kaplan-Meier methods. Cox-regression was utilized to calculate adjusted hazard ratios (HR). The median survival for the entire cohort was 12.2 months. The 1 year actuarial OS was 43.1 %, 53.3 %, and 64.3 % (p = 0.11), for intervals from surgery to radiotherapy of ≤ 2, 2-5, and ≥ 6 weeks, respectively. Patients radiated within 2 weeks post-surgery were more likely to have older age (p = 0.03), treated with 2D techniques (p < 0.001) and dose <36 Gy (p < 0.001), undergo a biopsy only (p < 0.001), KPS of <70 (p < 0.001), severe pre-radiotherapy neurologic symptoms (p = 0.04), and bilateral disease (p = 0.02). Multivariate analysis including MGMT status demonstrated a significant detriment in delaying radiotherapy (≤ 2 weeks as reference); 3-5 weeks (HR 2.80 [0.72-10.89], p = 0.14), and >6 weeks (HR 3.76 [1.01-14.57], p = 0.05). We report the first analysis on the survival impact of delaying post-operative radiotherapy for temozolomide treated glioblastoma patients with MGMT information. Our data does not support the OS benefit previously seen in delayed RT when correcting for important covariates. We demonstrate a survival detriment with delaying RT post-surgery greater than 6 weeks on multivariate analysis.