FET-PET-Guided Management of Pseudoprogression in Glioblastoma

The goal of this diagnostic randomised clinical trial is to determine, in glioblastoma patients with diagnostic uncertainty between pseudoprogression and tumor progression on follow-up MRI after chemoradiation, the added value of a direct \[¹⁸F\] FET-PET scan for clinical management. The main questions it aims to answer are: * Does the clinical management guided by an additional FET-PET scan leads to fewer unnecessary interventions, compared with management based on MRI only? * Does the clinical management guided by an additional FET-PET scan leads to better health-related quality of life after 12 weeks, compared with management based on MRI only? * Does the clinical management guided by an additional FET-PET scan leads to reduced net healthcare costs, compared with management based on MRI only? Researchers will compare the investigational arm, where clinical management is based on the index MRI scan and an additional FET-PET scan, with the control arm, where clinical management is based solely on the index MRI scan, to investigate the added value of the FET PET scan for clinical management. Participants in the investigational arm will undergo the FET PET scan. All participants will complete health-related quality of life questionnaires at four different timepoints.

Sex

All

Minimum age

18 Years

Inclusion Criteria:

* Patients with a glioblastoma, IDH-wildtype, World Health Organization (WHO) grade 4, according to WHO 2021 criteria.
* Age ≥18 years
* New or increased enhancement within the high-dose radiation field (defined as within the 80% isodose line) on follow-up MRI
* Follow up MRI ≥3 months after the end of the standard-of-care temozolomide-based concomitant chemoradiation (60 Gy/30 fractions or 40 Gy/15 fractions). Of note, very early increase - within 3 months of last radiation - will not be grounds for inclusion because of the high rate of pseudoprogression and slightly lower diagnostic performance of FET-PET compared to the situation of increase beyond 3 months after last radiation. Patients with such very early increase may have subsequent further increase after 3 months post-radiation, causing (further) diagnostic doubt; these may be included at that later timepoint if they meet the other inclusion criteria.
* First moment of clinicoradiological uncertainty regarding the diagnosis (≥3 months after the end of chemoradiation): pseudoprogression or tumor recurrence. The determination of 'uncertainty' is made by the treating physician, preferably in the multidisciplinary tumor board, based on available clinical and standard-of-care MRI-data, which generally includes perfusion-MRI.
* Previous usage of bevacizumab as a symptom treatment is allowed. However, inclusion is only allowed at the first moment of clinical doubt between pseudoprogression and tumor recurrence, not at later timepoints.

Exclusion Criteria:

* Previous treatment for recurrence of disease
* An enhanced lesion size of less than 1 cm on the index MRI. In the newest RANO PET criteria, it is advised to use FET-PET for increasing lesions only in cases with a minimum lesion size.
* Life expectancy of less than 6 months, determined by the treating physician
* Contra-indications for PET (claustrophobia, inability to lay still)
* Women of childbearing potential without adequate contraception
* Any other concomitant disease that may influence PET imaging or clinical outcomes of this study, this includes but is not limited to: cerebral inflammatory diseases and other cancers with brain- or leptomeningeal metastases

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