Abstract
We investigated the potential of [18F]fluorodeoxyglucose ([18F]FDG) and [18F]Fluoromethylcholine ([18F]FCho) PET, compared to contrast-enhanced MRI, for the early detection of treatment response in F98 glioblastoma (GB) rats. When GB was confirmed on T2- and contrast-enhanced T1-weighted MRI, animals were randomized into a treatment group (n = 5) receiving MRI-guided 3D conformal arc micro-irradiation (20 Gy) with concomitant temozolomide, and a sham group (n = 5). Effect of treatment was evaluated by MRI and [18F]FDG PET on day 2, 5, 9 and 12 post-treatment and [18F]FCho PET on day 1, 6, 8 and 13 post-treatment. The metabolic tumor volume (MTV) was calculated using a semi-automatic thresholding method and the average tracer uptake within the MTV was converted to a standard uptake value (SUV). To detect treatment response, we found that for [18F]FDG PET (SUVmean x MTV) is superior to MTV only. Using (SUVmean x MTV), [18F]FDG PET detects treatment effect starting as soon as day 5 post-therapy, comparable to contrast-enhanced MRI. Importantly, [18F]FDG PET at delayed time intervals (240 min p.i.) was able to detect the treatment effect earlier, starting at day 2 post-irradiation. No significant differences were found at any time point for both the MTV and (SUVmean x MTV) of [18F]FCho PET. Both MRI and particularly delayed [18F]FDG PET were able to detect early treatment responses in GB rats, whereas, in this study this was not possible using [18F]FCho PET. Further comparative studies should corroborate these results and should also include (different) amino acid PET tracers.
Highlights
In the US, 84,170 new cases of primary brain and other central nervous system tumors are estimated to be diagnosed in 2021
We found that for [18F]FDG PET (SUVmean x metabolic tumor volume (MTV)) is superior to MTV only
Because tumor volumes in individual animals were variable, tumor volume after the start of irradiation were normalized to the magnetic resonance imaging (MRI) tumor volume before starting therapy
Summary
In the US, 84,170 new cases of primary brain and other central nervous system tumors are estimated to be diagnosed in 2021. Surgical resection remains the most effective treatment for gliomas. It has been shown that patients who had a gross total resection have a better response to subsequent adjuvant treatments than those who underwent a partial resection or biopsy only [2]. In about half of the newly diagnosed patients, gross total resection is not possible [3]. For newly diagnosed glioblastoma (GB) patients with a good performance status, the standard of care includes maximal surgical resection followed by combined external beam RT (60 Gy in 30 fractions) and TMZ [4,5,6]. The identification of early treatment failure may reduce costs because new systemic treatments (e.g. bevacizumab) are considerably more expensive than conventional alkylating chemotherapy (e.g. lomustine) [7,8,9]
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