Radioactive iodine in the treatment of thyroid disease.

Since all isotopes of any element have identical chemical behaviour, the radioactive isotopes of iodine are metabolised in the same way as normal iodine, and become highly concentrated in normal or over-active thyroid tissue and, in some circumstances , in thyroid cancer tissue. It may consequently be possible to destroy part or all of such tissues by the effects of the intense local beta radiation emitted by the radioiodine which becomes concentrated in them, and to do so without causing undue radiation damage to other parts of the body, in which the radioiodine is only weakly or transiently concentrated. Normal or over-active thyroid tissue can readily be destroyed in this way without hazardous radiation of bone marrow, gonads or other organs, since iodine is highly concentrated and well retained in such tissues. In thyroid carcinoma, on the other hand, where iodine is less efficiently concentrated and is poorly retained, much larger doses are required and the progress of treatment is often limited by the need to avoid undue marrow depression. Radioiodine Treatment of Thyroid Carcinoma Radioactive iodine has considerable value in the treatment of many cancers of the thyroid 4, 7, 10, 11, 12, 13, 15 and the indications for its use in this disease depend upon a number of factors which are now becoming clearly established. I. The radical removal by surgery of all tumour tissue, where this is practicable, must always be regarded as preferable to radioiodine therapy. 2. Anaplastic thyroid carcinomata are unlikely ever to concentrate radioiodine, whereas a substantial majority of all differentiated tumours, including those of mainly papillary structure, are likely to concentrate radioiodine under suitable conditions of stimulation and may, therefore, become suitable for treatment by this means. 3. Even the histologically differentiated tumours do not usually concentrate radioiodine until the function of all normal thyroid tissue has been abolished, the uptake in the tumour commonly only developing with the advent of myxoedema two or three months after thyroid ablation. 4. The extent to which tumour tissue will be destroyed by the radiations from any radioiodine that is selectively concentrated in it will depend, not only on the efficiency and on the duration of such radioiodine concentration, but also on the radiosensitivity of the tumour. Good clinical results may, therefore, be obtained despite poor concentration, while tumours with good concentration may sometimes only respond slowly, if at all. 5. When the series of large …