This trial is a prospective, non-interventional, monocentric study aiming to collect standard of care imaging of patients treated with Iodine-131 for the determination of dosimetric studies.

Data from this study will be collected as part of an European research project called MEDIRAD.

The overall objectives of this project are to enhance the scientific bases and clinical practice of radiation protection in the medical field, and more specifically to develop and implement the tools necessary to establish the range of absorbed doses delivered to healthy organs in patients undergoing thyroid ablation and the threshold absorbed dose required for thyroid ablation. This will enable patient specific treatment planning that will minimize risk to the patient while ensuring a successful outcome and will facilitate development of a large scale epidemiological study of the effect of low absorbed doses from irradiation of normal organs with internal sources of radionuclides.

Patients will be followed as part of their standard of care. Imaging (SPECT/CT (Single Photon Emission Computed Tomography-Computerized Tomography) and Whole Body scintigraphy) performed at 48 hours post Iodine-131 treatment will be collected. Measures of external gamma radiation will also be collected in the European database.

Inclusion Criteria:

1. Patient with differentiated thyroid cancer (papillary or follicular) stage T1b, T2, T3A, Nx-N0-N1, M0 (according to AJCC 8th edition, 2017) of intermediate risk of recurrence (according to 2015 ATA Risk Stratification System)
2. Patient is eligible to receive a therapeutic activity of 3.7 GBq of I-131 after total thyroidectomy or completion thyroidectomy
3. Age ≥ 18 years old
4. Patient affiliated to the French social security system
5. Patient who has received an informed consent for the study

Exclusion Criteria:

1. Patient who has received an external radiotherapy within 6 weeks prior to I-131 treatment
2. Patient who has received a systemic chemotherapy within 6 weeks prior to I-131 treatment
3. History of treatment with I-131
4. Pregnant or breastfeeding women
5. Any psychological, familial, geographical or sociological condition potentially preventing the medical follow-up and/or study procedures
6. Patient protected by law

All patients with differentiated thyroid cancer and who are eligible for a Iodine-131 (I-131) treatment after a total thyroidectomy or completion thyroidectomy will be invited to join the study.