Upon joining the study, the patient is required to have undergone a total thyroidectomy, which is the surgical removal of the thyroid gland. This procedure must have been completed within 6 to 14 weeks before the patient is randomized into the trial.

The patient must have a normal post-operative neck ultrasound or, if the ultrasound is doubtful, a negative cytology and normal thyroglobulin (Tg) value in the fine needle aspiration (FNA) washout fluid.

The patient is randomly assigned to one of two groups: one receiving systematic radioiodine (RAI) treatment and the other receiving RAI treatment based on a post-operative work-up.

The post-operative work-up involves assessing serum thyroglobulin (Tg) levels and performing a diagnostic RAI scintigraphy, which is an imaging test to check for remaining thyroid tissue or cancer.

For patients in the systematic RAI treatment group, sodium iodide (131I) is administered orally in the form of hard capsules. The dosage ranges from 37 to 5550 MBq, depending on the specific needs of the patient.

Patients in the guided RAI treatment group receive sodium iodide (131I) only if the post-operative work-up indicates it is necessary.

Patients are monitored for their response to treatment at 1, 3, and 5 years post-randomization. The primary goal is to achieve an excellent response, which includes normal neck ultrasonography and specific thyroglobulin levels.

Additional assessments include evaluating the quality of life, anxiety, and fear of cancer recurrence through questionnaires. Toxicities affecting the lachrymal, nasal, and salivary glands are also assessed.

If necessary, supplemental treatments such as additional surgery or RAI administration may be performed within 5 years post-randomization. The response to these treatments is evaluated according to established guidelines.

The costs associated with these treatments, including consultations, hospitalizations, imaging exams, and transportation, are considered as part of the study.