Incidence and Extent of Disease Progression on MRI Between Surgery and Initiation of Radiotherapy in Glioblastoma Patients

Abstract

For patients with glioblastoma (GBM), the post-operative MRI (MRI1) is routinely used for radiation treatment planning, with radiotherapy starting within approximately 6 weeks of surgery. Some patients may also undergo an additional MRI (MRI2) prior to starting radiotherapy due to new symptoms, as a part of radiation therapy planning, or as a requirement of clinical trial enrollment. We sought to retrospectively analyze the incidence and extent of disease progression on MRI between surgery and initiation of radiotherapy in GBM patients.From our institutional oncology database, we identified 137 patients with GBM diagnosed between 2018-2020. Of these patients, 56 had both an MRI1 and a pre-radiotherapy MRI2 available for assessment of disease progression. RANO criteria was utilized to identify patients with disease progression. The resection cavity and enhancing disease on the MRI1 and MRI2 were contoured to create post-operative and pre-radiotherapy GTV2 volumes in order to assess changes in volume between these two time points.Surgery consisted of a gross total resection in 38% (21/56) of patients and a subtotal resection in 62% (35/56) of patients. Median time between MRI1 and MRI2 was 26 days. Indications for MRI2 included new symptoms 11% (6/56), radiotherapy planning 27% (15/56), and clinical trial enrollment 62% (35/56). Disease progression was identified in 70% (39/56) of patients. Patients who had a subtotal resection were more likely to have disease progression (OR 5.3, P = 0.008) while age, performance status, time to MRI2, MGMT methylation status, IDH status, and EGFR amplification were not found to be associated with increased risk of disease progression. The mean and median volume of the MRI2 GTV2 that was not covered by the MRI1 GTV2 volume was 14cc3 (28% of the MRI2 GTV2 volume) and 7cc3 (26% of the MRI2 GTV2 volume), respectively. In 21% (8/39) of patients, disease progression would not have been encompassed by a 2cm expansion on the MRI1 GTV2 volume.This study adds further evidence that a significant number of patients with glioblastoma have disease progression between surgery and initiation of radiotherapy. Additionally, this study provides evidence for the potential impact of using MRI2 for radiation treatment planning given the incidence of disease progression extending outside a standard 2cm CTV expansion. Using a pre-radiotherapy MRI2 for treatment planning may allow for improved coverage of gross disease within radiation treatment fields, particularly in patients who underwent a subtotal resection.R.D. Kraus: None. C.R. Weil: None. F. Su: None. L.M. Burt: ARRO executive committee. J. Mendez: None.