Radionuclides and therapy of thyroid cancer

The majority of thyroid carcinomas are removed surgically. The appropriate surgical technique is still debated. After surgery the amount of residual thyroid or tumour and the presence of local or distant metastases is often in doubt, particularly if it is not detectable clinically. Therefore, methods for determining the presence of disease or the later recurrence of disease are needed. They commonly include serum thyroglobulin and imaging after diagnostic or therapeutic doses of 131I. Other techniques are used such as 131I whole body retention (using a whole body counter), 201Tl and 99Tcm-sestamibi imaging. The place of these diagnostic methods in the management of thyroid cancer is reviewed in this article. Radioiodine would seem an ideal treatment for recurrence of functioning thyroid carcinoma as 131I targets the lesion and has minimal side effects. However, the indolent nature of well-differentiated thyroid carcinomas makes it difficult to assess the benefits of radioiodine therapy both in its ability to ablate the normal thyroid and to treat recurrent and metastatic disease. However, the addition of radioiodine therapy to local surgical removal reduces both the occurrence of metastases and the morbidity with prolonged follow-up. Unresolved issues that remain concern the activities of radioiodine needed to achieve adequate ablation of residual thyroid tissue and to treat residual and recurrent cancer. There is also debate as to exactly which patients require radioiodine therapy. This review also considers radiation protection and the side effects of 131I therapy.