Timing of adjuvant radiotherapy in glioblastoma patients: A single-institution experience with more than 400 patients

BACKGROUND: The standard of care for patients with newly diagnosed glioblastoma (GBM) is maximal safe resection followed by adjuvant radiation therapy (RT) and temozolomide (TMZ). OBJECTIVE: To investigate whether the timing of adjuvant RT after surgery affected outcome in patients with GBM. METHODS: We retrospectively reviewed all patients with a diagnosis of GBM at our institution. A total of 447 patients were included in our analysis. Patients were divided into 3 equal groups based on the interval between surgery and RT. The primary outcome was overall survival (OS). RESULTS: Patients who began RT less than 21 days after surgery tended to be older, have a lower a Karnofsky Performance Status score, and higher recursive partitioning analysis class. These patients were more likely to have undergone biopsy only and received 3-dimensional conformal RT or 2-dimensional RT. The median OS for patients who started RT less than 21 days after surgery, between 21 and 32 days after surgery, and more than 32 days after surgery was 374, 465, and 478 days, respectively (P .004). On multivariate Cox regression analysis, Karnofsky Performance Status score lower than 70, undergoing biopsy only, recursive partitioning analysis classes IV and V/VI, use of less than 36 Gy RT, and lack of TMZ chemotherapy were predictors of worse OS. The interval between surgery and RT was not significantly associated with OS on multivariate analysis. CONCLUSION: Patients who begin RT less than 21 days after surgery tend to have worse prognostic factors than those who begin RT later. When accounting for significant covariates, the effect of timing between surgery and RT is not significant. ABBREVIATIONS: GBM, glioblastoma GTR, gross total resection IDH1, isocitrate dehydrogenase 1 MGMT, O-6-methylguanine-DNA-methyltransferase OS, overall survival RPA, recursive partitioning analysis RT, radiation therapy STR, subtotal resection TMZ, temozolomide.