The Role of ¹²³I in the Management of Differentiated Thyroid Cancer: A Comprehensive Narrative Review.

Differentiated thyroid carcinoma (DTC) is the most common malignant endocrine tumor, with a generally favorable prognosis. Imaging, including iodine radioactive isotope scintigraphy (IRIS), is crucial for diagnosis and follow-up. While ¹³¹I has long been used for both therapeutic and diagnostic purposes, ¹²³I is reserved for diagnostic imaging due to its shorter half-life and γ emissions. This review highlights the utility of ¹²³I scintigraphy, especially in pre-treatment assessment and dosimetry for DTC. It is particularly valuable before radioiodine (RAI) ablation, providing accurate imaging in patients with iodine-refractory (IR) or biochemically incomplete response (BIR) DTC. When compared to post-therapeutic ¹³¹I scans, ¹²³I scintigraphy appears to have a lower sensitivity for detecting metastatic lesions, particularly in lymph nodes and lungs. However, its diagnostic performance compared to low-dose diagnostic ¹³¹I is more variable, with some studies suggesting superiority due to the absence of stunning. Further research is needed to standardize its use and optimize its role in guiding DTC management.