Patient follow-up includes, as a minimum, out-patient appointments with cervical ultrasound and measurement of serum TSH, hTG, anti-Tg antibodies and a blood count 2 and 8 months after each RIT or WBS, and a WBS (with at least 200 MBq over at least 48 h) under endogenous TSH-stimulation 3 and 12 months after ablative RIT and then at 24-month intervals. FDG-PET and other imaging modalities can be performed if needed. At each follow-up appointment, RTx toxicity is recorded according to RTOG criteria and quality of life by the QLQ-C30 questionnaire (v. 3.0 German) of the EORTC.