In France, 3,700 new cases of thyroid cancer are diagnosed each year. Differentiated thyroid carcinoma represents more than 90% of all thyroid cancers; and has a 10-year survival of 90-95% of patients. This favorable prognosis is the result of an effective primary therapy, which consists of a total thyroidectomy that is followed by radio-iodine ablation with 3,7GBq (100mCi) in case of significant risk of persistent disease. Few centers investigated the possibility to administer lower doses of 131I (1GBq, 30 mCi), in order to limit the potential long-term adverse complications for patients and to respond to radioprotection rules for family members and medical staff.

Radio-iodine ablation requires TSH stimulation, which was historically achieved by thyroid hormone withdrawal for 3 to 5 weeks. During this period, patients suffered from symptoms of hypothyroidism. The recombinant human TSH (rhTSH, Thyrogen®, Genzyme Therapeutics, Cambridge, USA) was approved in Europe in 2005 as an alternative stimulation procedure to withdrawal during ablation. It allows patients to remain euthyroid on thyroid hormone therapy (that needs not to be withdrawn). However, this a costly drug (800 € per patient), whose economic efficiency needs to be checked.

This is a multicentric, randomized, controlled, open-label phase III clinical trial involving 26 French centers. It aims at comparing four strategies of management of postoperative radioiodine ablation, each strategy combining a method of TSH stimulation (thyroid hormone withdrawal or rhTSH (Thyrogen®, Genzyme)) and an activity of 131I (low-dose (1GBq, 30 mCi) or high-dose (3,7GBq, 100 mCi)).

Inclusion Criteria:

• 18 year or older
• Newly diagnosed differentiated papillary or follicular thyroid carcinoma who underwent total thyroidectomy between 30 and 60 days before randomization and treated by LT4 for at least one month.
• Patients are all staged pT1<1cm N1 or pT1>1cm N0 N1 Nx or pT2 N0
• The performance status is 0 or 1.
• All patients will provide written consent to participate.

Exclusion Criteria :

• partial thyroidectomy
• patients treated by LT4 less than one month
• time from thyroidectomy superior to 60 days at randomization
• patients with Hurtle cancer or aggressive histology
• Patients staged pT1<1cm N0 or T2 N1 or T3 or T4 or M1
• patients for which the use of rhTSH is required for medical reasons
• patients with major concurrent medical disorder (cardiac, renal, liver, respiratory)
• patients with other malignancies (exception for in situ cervix uterine cancer, baso cellular skin cancer or breast cancer in remission for at least 2 years)
• patients with recent history of drugs affecting thyroid function, including iodine containing medications or radiocontrast agents
• patients with recent history of 131I whole body scan
• pregant women or breast-feeding