What is your approach to determining recurrent versus RAI-refractory differentiated thyroid cancer in patients presenting with metastatic disease several years after surgery?  

It sounds like you already know that there is a non-iodine avid distant disease. A brain MRI is recommended to exclude CNS disease. If insurance allows, go to a PET/CT with a diagnostic CT of the neck and chest. If insurance will not allow PET, then diagnostic CT of the neck, chest, and abdomen with...