%0 Journal Article %A Marcus Unterrainer %A Katharina von Rohr %A Lena Kaiser %A Caroline Diekmann %A Viktoria Ruf %A Jochen Herms %A Peter Bartenstein %A Maximilian Niyazi %A Joerg Tonn %A Nathalie Albert %T Biological-tumor-volumes in standard and early summation 18F-FET PET images distinctly exceed contrast-enhancement in patients with IDH-wildtype glioma %D 2019 %J Journal of Nuclear Medicine %P 1504-1504 %V 60 %N supplement 1 %X 1504Background: In patients with IDH-wildtype glioma, the contrast-enhancement (CE) on MRI usually represents the target of local treatments such as resection and radiotherapy. PET using 18F-FET enables detection of metabolically active tumor parts beyond CE on MRI. Especially, even larger metabolically active parts are seen in early 18F-FET PET summation images. However, the spatial correlation of CE and PET-derived tumor volumes in IDH-wildtype gliomas remains unknown and was analysed in this study. Methods: Patients with de-novo IDH-wildtype glioma WHO grade III/IV undergoing 18F-FET PET and MRI prior to any further therapy were included. On 18F-FET PET, the biological-tumor-volume (BTV) was assessed (1.6 x background-activity) within standard (20-40 minutes) and early (5-15 minutes) summation images (eBTV). On MRI, the volume of CE was delineated. The spatial correlation between CE, BTV and eBTV was assessed using the Dice-similarity-coefficient (DSC). The respective DSCs were then correlated with the individual histological and molecular genetic features (i.e. WHO grade, MGMT-methylation and TERT-promoter mutation). Results: 164 patients with IDH-wildtype glioma were included (99/164 (60%) glioblastoma WHO grade IV, 65/164 (40%) anaplastic astrocytoma WHO grade III). Of these, 157/164 (96%) were 18F-FET-positive and 130/164 (79%) showed CE on MRI. 27/34 (79%) patients without CE were 18F-FET-positive; vice versa, 0/7 (0%) 18F-FET-negative patients showed CE on MRI. Overall, CE was significantly smaller than BTV (13.6±18.5 vs. 26.6±24.8 ml, p<0.001) and eBTV (32.1±26.7 ml, p<0.001), whereas eBTV was significantly larger than BTV (32.1±26.7 vs. 26.6±24.8 ml, p=0.001). Hence, there was a poor spatial correlation of CE / BTV (DSC 0.31±0.22) and CE / eBTV (DSC 0.33±0.21), but a moderate spatial correlation of BTV and eBTV (DSC 0.75±0.19). The DSC was significantly lower in WHO grade III compared to WHO grade IV gliomas correlating CE / BTV (DSC 0.22±0.21 vs. 0.34±0.21, p=0.005) and CE / eBTV (DSC 0.26±0.21 vs. 0.36±0.21, p=0.024), whereas the DSC was independent of MGMT and TERT (p>0.05 each). Conclusions: In IDH-wildtype gliomas, the PET-derived BTVs distinctly exceed the CE on MRI in both standard and early summation images with a poor spatial correlation only. Moreover, eBTV also exceeds BTV with a moderate spatial correlation. These vast spatial discrepancies suggest that metabolically active tumor on 18F-FET PET should be implemented into resection and radiotherapy planning, especially in case of IDH-wildtype glioma without CE on MRI. %U