502 Imaging Timing After Surgery for Glioblastoma: Results From an International, Multi-Center Study (INTERVAL-GB)

INTRODUCTION: Glioblastoma is the most common malignant primary brain tumor in adults. Post-operative MRI is used to assess extent of resection, monitor treatment response and detect progression. However, compliance with accepted guidelines for follow-up MRI, and impact on patient management and outcomes is unclear. METHODS: Multi-center, international, retrospective observational cohort study of patients with confirmed WHO grade 4 glioma (Operated August 2018-February 2019) receiving oncological treatment, with follow-up to May 2022). RESULTS: There were 754 patients from 26 neuro-oncology centers with a median age of 63 years (IQR 54-70), yielding 10,100 (median, 12.5/person, IQR 5.2-19.4) person-months of follow-up. Of patients receiving debulking surgery, most patients had post-operative MRI within 72 hours of surgery (78.0%, N=407/522), and within 48 hours of surgery (64.2%, N=335/522). The median number of subsequent follow-up MRI scans was 1 (IQR 0-4). Compliance with NICE and EANO recommendations for follow-up MRI was 52.8% (N=398/754) and 24.9% (N=188/754), respectively. On multivariable Cox regression analysis, increased time spent in recommended follow-up according to NICE guidelines was associated with longer OS (HR 0.56, 95% CI 0.46-0.66, P<0.001), but not PFS (HR 0.93, 95% CI 0.79-1.10, P=0.349). Increased time spent in recommended follow-up according to EANO guidelines was associated with longer OS (HR 0.54, 95% CI 0.45-0.63, P<0.001) but not PFS (HR 0.99, 95% CI 0.84-1.16, P=0.874). CONCLUSIONS: Regular surveillance follow-up for glioblastoma is associated with longer OS. Prospective trials are needed to determine whether regular or symptom-directed MRI influences survival outcomes, treatment decisions, and quality of life.