Patients who consented to randomization at centers actively taking part in randomization were randomized to treatment arms A (additional adjuvant RTx) and B (no RTx) 3 months after initial RIT after confirmation of the histological diagnosis by the reference pathologist and when distant metastases had been excluded by means of serum thyroglobulin (Tg), WBS (s. a.) and a native thoracic computed tomogram (CCT). Randomization was stratified according to histological type (papillary v. follicular), nodal status (pN0/1/x), and participating center, and performed by an operator-independent randomization routine embedded in the database. The remaining patients were assigned to arms A and B by the participating centers.