The aim of this study is to assess the recurrence-free survival (RFS) rate and recurrence-related factors, especially the relationship between RFS and RAI dose, in patients who received RAI after thyroidectomy.

Thyroid cancer is the most frequent cancer of the endocrine system, and its incidence is constantly rising worldwide. This is mainly because of advances in examination modalities that have made it possible to detect smaller cancers at an early stage.

Owing to advancements in screening techniques and treatment methods, the number of patients who die from thyroid cancer is small compared to the incidence.[1]

The most common type of thyroid cancer is differentiated thyroid cancer (DTC), which includes papillary and follicular carcinomas. Women are three times more likely to develop thyroid cancer than men. [2] Adjuvant RAI131 (AT) is recommended post thyroidectomy, because of its therapeutic impact on micro-invasions or micro-metastases, to reduce the likelihood of recurrence in patients who do not have metastases but have risk of recurrence according to the Japanese guidelines and American Thyroid Association guidelines [3],[4].

AT could prolong the survival of patients with intermediate-risk DTC [5]. Additionally, a meta-analysis has shown that AT is effective in reducing recurrence in some studies but not in others, and the effect of AT on recurrence prevention, especially in high-risk DTC, remains unclear.[6].

Although there are reliable reports discussing the relationship between the success or failure of remnant ablation [7],[8], recurrence after AT is rarely reported and the number of cases is small. In addition, no study has so far discussed the relationship between the success or failure of AT or remnant ablation and recurrence or death [9],[10].

Inclusion Criteria:

• Patients with DTC (differentiated thyroid cancer) who underwent total or subtotal thyroidectomy without distant metastasis and gross residual tumors.
• Followed by ablation with RAI and underwent post RAI whole body scan.
• Having baseline TG (thyroglobulin), Anti-TG antibodies (anti thyroglobulin) and neck US.
• Patients with lymph node metastasis will be included if their lymph nodes had been dissected and no unresectable disease remained.

Exclusion Criteria:

• Patients who received RAI and missed follow-up.
• Patients with no surgical or pathological data.

patients with differentiated thyroid cancer underwent total thyroidectomy.