FET PET reveals considerable spatial differences in tumour burden compared to conventional MRI in newly diagnosed glioblastoma
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Areas of contrast enhancement (CE) on MRI are usually the target for resection or radiotherapy target volume definition in glioblastomas. However, the solid tumour mass may extend beyond areas of CE. Amino acid PET can detect parts of the tumour that show no CE. We systematically investigated tumour volumes delineated by amino acid PET and MRI in patients with newly diagnosed, untreated glioblastoma.
Preoperatively, 50 patients with neuropathologically confirmed glioblastoma underwent O-(2-[18F]-fluoroethyl)-l-tyrosine (FET) PET, and fluid-attenuated inversion recovery (FLAIR) and contrast-enhanced MRI. Areas of CE were manually segmented. FET PET tumour volumes were segmented using a tumour-to-brain ratio of ≥1.6. The percentage overlap volumes, and Dice and Jaccard spatial similarity coefficients (DSC, JSC) were calculated. FLAIR images were evaluated visually.
In 43 patients (86%), the FET tumour volume was significantly larger than the CE volume (21.5 ± 14.3 mL vs. 9.4 ± 11.3 mL; P < 0.001). Forty patients (80%) showed both increased uptake of FET and CE. In these 40 patients, the spatial similarity between FET uptake and CE was low (mean DSC 0.39 ± 0.21, mean JSC 0.26 ± 0.16). Ten patients (20%) showed no CE, and one of these patients showed no FET uptake. In five patients (10%), increased FET uptake was present outside areas of FLAIR hyperintensity.
Our results show that the metabolically active tumour volume delineated by FET PET is significantly larger than tumour volume delineated by CE. Furthermore, the results strongly suggest that the information derived from both imaging modalities should be integrated into the management of patients with newly diagnosed glioblastoma.
KeywordsFET PET tumour volume Volumetry Amino acid PET MRI contrast enhancement FLAIR hyperintensity Target volume definition
The authors thank Suzanne Schaden, Trude Plum, Natalie Judov, Silke Frensch, Kornelia Frey and Lutz Tellmann for assistance with the patient studies, and Johannes Ermert, Silke Grafmüller, Erika Wabbals and Sascha Rehbein for radiosynthesis of FET.
This study was funded by Wilhelm Sander-Stiftung, Munich, Germany (grant number 2016.069.1 to N.G.)
Compliance with ethical standards
Conflicts of interest
All procedures performed in studies involving human participants were in accordance with the ethical standards of the institutional and/or national research committee and with the principles of the 1964 Declaration of Helsinki and its later amendments or comparable ethical standards. For this type of study formal consent is not required.
Informed consent was obtained from all individual participants included in the study.
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