ESTRO 2021 Abstract Book

S889

ESTRO 2021

In this prospective, single centre pilot study patients received standard-of-care biopsy or resective surgery followed by concurrent chemoradiotherapy (60 Gy in 30 fractions with concurrent temozolomide). 18 F- fluciclovine PET-CT and multi-parametric MRI (mpMRI) including DCE-MRI were acquired at 3 time points: before, during and after radiotherapy. DCE-MRI data were post-processed generating transfer coefficient (K trans ) and interstitial volume (V e ) maps, and these along with PET and CT images were rigidly co-registered to Gd-T1. PET, DCE-MRI and Gd-T1 volumes were contoured at each scan timepoint. Tumour segmentation on PET was defined using 2, 3 and 4 times maximum standardised uptake value (SUV max ) thresholds. Gd-T1, K trans and V e images were manually contoured. The Gd-T1 volume was subtracted from PET and DCE-MRI volumes to identify areas beyond the Gd-T1 contour boundary. Subtracted contour similarity was evaluated with the Dice similarity coefficient. Results 6 patients (GBM 1 - 6) with glioblastoma were recruited. GBM 1-3 (poor outcome group) had lower overall survival than patients 4-6 (good outcome group) - mean 244 vs 720 days. GBM 1-3 had unmethylated MGMT status whilst GBM 4 and 5 had methylated MGMT status. MGMT status was unknown for GBM 6. In the poor outcome group, PET volumes were larger than DCE-MRI, which, were larger than the Gd-T1. In the good outcome group, the Gd-T1 contour was larger than the PET contour, for 2/3 of the thresholds used and DCE-MRI contours were similar to Gd-T1 ( Table 1 ). Findings were consistent across different PET thresholds.

With the Gd-T1 contour subtracted from PET and DCE-PWI, tracer uptake and DCE-MRI uptake was seen outside of the Gd-T1 contour, across all 3 PET thresholds. Comparing PET and DCE-MRI in the subtracted images, the Dice similarity coefficients were low suggesting distinct areas of fluciclovine and Gd uptake. Visual differences in PET and DCE-MRI contours are illustrated in Figure 1 .

Conclusion 18 F-fluciclovine -PET and DCE-MRI may offer complementary information to conventional Gd-T1 MRI in the monitoring of treatment response to chemoradiotherapy. These preliminary results suggest smaller PET