Interventions: A [18F]dabrafenib PET/CT scan and an MRI scan of the brain will be performed at baseline, 7 days or less before the start of treatment with oral dabrafenib. CT and MRI are part of the regular care. The PET procedure commence with the injection of approximately 200 MBq [18F]dabrafenib, which is followed by a 60 minutes dynamic PET scan of the brain and thereafter a total-body PET scan (toe to head). During the dynamic PET scan of the brain, arterial blood sampling and analysis of plasma metabolites will be performed. Treatment response will be monitored as part of the regular treatment (CT for thorax/abdomen and MRI for brain) after 4 weeks. In addition, a single venous blood sample will be collected for isolation of circulating tumor DNA. Immunohistochemical staining for mutated B-raf protein will be performed on tumor tissue, either derived from a fresh biopsy or from a preexisting tumor specimen.