RTx is begun after documented elimination of cervical I-131 uptake in a I-131 WBS 3 months after the last fraction of ablative RIT. RT includes the thyroid bed (in unilateral tumors only the affected side) with a dose of 59.4 Gy and 66.6 Gy after R0 and R1 resection, resp., and the regional lymph nodes of the neck and upper mediastinum including the posterior cervical chain from the mandible and mastoid process to the tracheal bifurcation with a dose of 50.4 Gy and 54.0 Gy in pN0 and pN1/x disease, resp. Fractionation is conventional (1.8 Gy/d 5 days a week). 3-D planning according to IRCU 50 is mandatory.