Which radionuclide is primarily used in the treatment of thyroid cancer?

Iodine-131 (I-131) is primarily used in the treatment of thyroid cancer due to its unique radioactive properties that allow it to be selectively taken up by thyroid tissue. The thyroid gland naturally absorbs iodine from the bloodstream, which facilitates the targeted destruction of cancerous cells. When I-131 is administered, it emits both beta and gamma radiation. The beta particles have a direct therapeutic effect, destroying malignant cells in the thyroid while the gamma radiation can be used for imaging and monitoring the distribution of the radionuclide within the body.

This selectivity makes I-131 particularly effective in treating conditions such as differentiated thyroid carcinoma (DTC), where thyroid cells, including tumor cells, retain the ability to concentrate iodine. Moreover, the ability to use I-131 not only for treatment but also for post-surgical ablation and in diagnostics (such as in the evaluation of thyroid function) adds to its utility in managing thyroid cancer effectively.

In contrast, the other radionuclides listed are not primarily utilized for treating thyroid cancer. I-125 is mainly used in brachytherapy for treating prostate cancer and for some diagnostic purposes. Technetium-99m (Tc99m) is primarily used for imaging studies due to its short half-life