By its dual gamma and beta emission, 1311 permits both external detection and selective irradiation of residual or metastatic differentiated thyroid carcinoma. Indications based on the evaluation of prognostic factors and on the quality of surgical excision are more advisable than systematic use. Useless, even harmful after unilateral surgery decided because of a very good prognosis, I-131 is recommended according to several retrosprctive studies for post surgical ablation of the remnants, the detection and the treatment of the recurrences and the distant metastases. The use of therapeutic doses in patients with an isolated elevation of thyroglobuline (Tg) without any clinical or radiological signs favors early diagnosis and cure of metastases must be negative diagnostic scintigraphy. Dosimetric considerations and radioprotection measures must be guided by specific rules concerning radiometric material, adapted rooms and skilful personnel. Scintigraphic detection must be done in the best technical conditions. Protracted follow-up is based on Tg dosages and I-131 whole body scintigraphies. Early diagnosis of metastases and positive response to I-131 irradiation influence favorably remission rates. Even if a complete remission is nor achieved repeated treatments by a specialized team improve the quality of survival for metastatic patients.
