[18F]FET PET Imaging for Early Response Assessment of Bevacizumab in Recurrent Glioblastoma
Shivani Chiranth, Otto Mølby Henriksen, Benedikte Hasselbalch, Kirsten Grunnet, Jonathan Frederik Carlsen, Hans Skovgaard Poulsen, Ian Law, Karine Madsen, Thomas UrupAbstract
Background
Bevacizumab combination therapy has shown response in approximately 25% of recurrent Glioblastoma (GBM) patients. This study aimed to investigate the value of O-(2-18F-fluoroethyl)-L-tyrosine positron emission tomography ([18F]FET PET) imaging and the relevance of the PET-based response assessment criteria for diffuse gliomas (PET RANO) criteria in assessing response to bevacizumab combination therapy in recurrent GBM.
Material and methods
All recurrent GBM IDH-wildtype patients treated with bevacizumab plus irinotecan at Rigshospitalet (year 2018-2022) and evaluated with consecutive [18F]FET PET imaging at baseline and after 2 cycles of treatment were included. Metabolic tumour volumes (MTV), maximum tumour-to-background ratios (TBRmax), mean tumour-to-background ratios (TBRmean) and associated changes were determined. Cox regression and receiver operating characteristic analyses were used to identify predictors of survival beyond the median overall survival (OS).
Results
82 patients (median OS 9.3 months, 95% Confidence interval: 8.3–10.4) were included. Tumours were smaller and less metabolically active at follow-up. PET RANO showed a 68% response rate and was independently associated with a longer OS (p < 0.001). Analysis of individual PET parameters identified three thresholds that independently predicted longer OS with response rates of 35–40%: i) more than 76% reduction in MTV, ii) more than 21% reduction in TBRmax iii) follow-up MTV under 3.5 cm3.
Conclusion
On using [18F]FET PET for response assessment during bevacizumab treatment, the proposed response criteria improved identification of responders when compared with the PET RANO criteria. Nevertheless, further refinement and validation is needed to enhance PET-based response assessment.