Pretreatment T2-Weighted Fluid Attenuated Inversion Recovery (T2-FLAIRpre) MRI May Improve Gross Tumor Volume Delineation for Recurrent Glioblastoma Treated with Salvage Hypofractionated Stereotactic Radiation Therapy

Abstract

Few treatment options exist for recurrent GBM. HFSRT has been used as a salvage treatment strategy. Gross tumor volume (GTV) is usually based on pretreatment contrast enhanced T1-weighted (T1-contrastpre) MR image. T2-FLAIRpremay detect additional subtle signal of tumor infiltration. This study aimed to investigate the patterns of recurrence following salvage HFSRT using T2-FLAIR image in addition to T1-contrast in target delineation for HFSRT. We retrospectively examined 13 patients with recurrent GBM treated with HFSRT from 2015 to 2017 who had local recurrence following HFSRT. A median dose of 30 (25-35) Gy in 5 to 10 fractions was delivered. The median time between HFSRT and recurrence after HFSRT was 178 (48-259) days. Diagnostic MRI was performed before and 4 weeks after HFSRT, and then every 4 - 8 weeks. Separate GTVs using T1-contrastpre only, T2-FLAIRpre only, or T1pre+T2pre, were contoured blindly by a single radiation oncology physician. Recurrence volume was delineated on the post-treatment T1-contrast (T1-contrastpost) MRI at the time of progression. The volume overlapping between pretreatment GTV and recurrence volume was calculated. The centroid distance between pre- and post-treatment volumes was measured as well. Wilcoxon test was used to assess the statistical significance of differences. The median volumes overlapping between T1-contrastpre, T2-FLAIRpre, T1pre+T2pre and T1-contrastpost were 18% (range: 0-100%, Q1: 12%, Q3: 40%), 52% (range: 0-90%, Q1: 24%, Q3: 59%) and 53% (range: 0-100%, Q1: 26%, Q3: 77%), respectively. The recurrent volume overlapping with T1pre+T2pre was significantly larger than the overlap with T1-contrastpre (p=0.003). The median volume difference between T1-contrastpre and T2-FLAIRpre volumes resided in the recurrence volume was 3.9 cm3 (range: 0-11.5 cm3, Q1: 0.2 cm3, Q3 5.6 cm3). The centroid distance between volumes did not show significant difference. The median centroid distances between recurrence volume and T1-contrastpre volume, T2-FLAIRpre volume, and T1pre+T2prevolume were 1.3 cm (range: 0.3-4.9 cm, Q1: 0.8, Q3: 2.00), 1.3 cm (range: 0.3-4.7 cm, Q1: 0.8 cm, Q3: 2 cm) and 1.2 cm (range: 0.2-1.2 cm, Q1: 0.7 cm, Q3: 2.1 cm), respectively. A significant volume of recurrence occurred in the T1pre+T2pre region beyond the T1-contrastpre region. Further studies to investigate techniques incorporating T2-FLAIRpreregion may improve GTV delineation for salvage HFSRT.Abstract 3551; TableT1-contrastpreT2-FLAIRpreT1pre+T2preTarget overlappingDistance (cm)Target overlappingDistance (cm)Target overlappingDistance (cm)Maximum99%4.9100%4.7100%4.6Q340%2.059%2.077%2.1Median18%1.352%1.353%1.2Q112%0.824%0.826%0.7Minimum0%0.30%0.30%0.2 Open table in a new tab