Indications for Radio-iodine Treatment of Thyroid Carcinoma

Abstract

Certain thyroid carcinomata resemble normal thyroid tissue in having the capacity to concentrate iodine. Since radioactive iodine is chemically indistinguishable from normal iodine, such tumours will selectively con centrate radio-iodine. They may therefore be selec tively irradiated by the intense local beta radiation which is emitted from radio-iodine. If the local con centration and retention of radio-iodine in the tumour is high enough relative to that in other body tissues, the local radiation within the tumour may be great enough to cause its destruction, without causing fatal or toxic effects in the body as a whole. In principle, therefore, the selection of cases for such treatment is simple. Complete surgical excision remains, of course, the treatment of choice if ever it is possible (Dobyns, 1951) ; otherwise, radio-iodine should be used to treat any thyroid carcinoma which can be shown, or can be induced, to take up radio-iodine sufficiently. In practice, this criterion is complicated by several considerations. First, the detection of radio-iodine up take, and the judgment of its adequacy, may be difficult, particularly if the tumour is adjacent to normal thyroid tissue and if repeated biopsies cannot conveniently be made. Secondly, uptake may be demonstrable after total thyroidectomy in a tumour in which no uptake could be detected before the thyroid was removed. It may therefore be necessary to select for thyroid abla tion* those cases in which uptake cannot be shown but is likely to be demonstrable after thyroidectomy. This decision will be based on such indirect evidence as the histological differentiation of the tumour and perhaps its rate of growth. In such cases tests for uptake are repeated after thyroid ablation, and radio iodine treatment is started if adequate retention can be demonstrated.