Real-world Data on Intermediate-risk Differentiated Thyroid Cancer Biochemical Response to 3700 or 5550 MBq of [131I]Sodium Iodide

Background: The ideal [131I]Sodium Iodide activity for intermediate-risk thyroid cancer treatment is still uncertaindue to the high heterogeneity of this disease in these patients. Objective: The objective of this study is to compare the biochemical responses to radioiodine therapy (RIT) of intermediate-risk thyroid cancer patients administered [131I]Sodium Iodide at 3700 MBq (100 mCi) and 5550 MBq (150 mCi) activities. Methods: A retrospective study was conducted by reviewing the medical records of intermediate- risk thyroid cancer patients who received RIT between 2016 and 2020 at a reference cancer hospital in Brazil. Sociodemographic and clinical data were evaluated at the time of diagnosis. Clinical data during two years of follow-up were reviewed, and biochemical responses were determined according to the American Thyroid Association (ATA, 2015 version). Responses to 3700 MBq (100 mCi) and 5550 MBq (150 mCi) of [131I]Sodium Iodide were compared. Results: No significant statistical differences were observed concerning the biochemical therapeutic responses of patients treated with 3700 MBq or 5550 MBq (p = 0.088). The presence of nodal metastasis and positive pre-RIT thyroglobulin did not influence biochemical responses to radioiodine. Conclusion: Intermediate risk thyroid-cancer patients presented similar therapeutic responses to 3700 MBq and 5550 MBq [131I]Sodium Iodide activities.