Assessment of therapy response to Regorafenib by 18 F-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 18 F-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 18 F-DOPA PET/CT within 1 week before and at 8-week intervals after REG therapy. 18 F-DOPA PET was analyzed using qualitative and quantitative approaches. For the quantitative analysis, maximum (SUV max ), mean standardized uptake values (SUV mean ) 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 SUV max , SUV mean 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 18 F-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 18 F-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.