Assessment of therapy response to Regorafenib by 18F-DOPA-PET/CT in patients with recurrent high-grade gliomas: a case series

Purpose: Regorafenib (REG) has been recently approved for the treatment of relapsed glioblastoma. Contrast-enhanced (CE) magnetic resonance (MR) imaging represents the gold standard for diagnosis and surveillance of brain tumors. We evaluated the potential role of 18F-DOPA PET/CT in determining the response to REG in a case series of patients with recurrence of high-grade gliomas. Methods: Three patients with recurrence of high-grade gliomas underwent CE-MR and 18F-DOPA PET/CT within 1 week before and at 8-week intervals after REG therapy. 18F-DOPA PET was analyzed using qualitative and quantitative approaches. For the quantitative analysis, maximum (SUVmax), mean standardized uptake values (SUVmean) and metabolic tumor volume (MTV) were obtained. Results: In two patients, an early metabolic response to REG treatment, both visually and in terms of reduction of SUVmax, SUVmean and MTV, was observed. In one subject, no metabolic response was detected. Metabolic PET data were in agreement with morphological and perfusion MRI data in two patients. In one patient, while 18F-DOPA was able to correctly diagnose a metabolic response to REG, MRI had misdiagnosed a pseudo-progression of the disease. Discussion: These preliminary findings suggest that 18F-DOPA PET/CT allows an early and reliable assessment of metabolic response to the REG treatment. A major advantage of PET seems to be obtained in patients in whom MR is unable to differentiate non-response vs tumor pseudo-progression