Clinical Experience in Diagnosis and Treatment of Thyroid Disorders with Radioactive Iodine (Eight-Day Half-Life)

IT IS WELL KNOWN that the thyroid gland takes up iodine (1). When radioactive isotopes of this element became available, tracer studies were carried out to discover what portion of an administered amount lodged in the gland, and what became of the remainder (2, 3). In this first work, the radioactive iodine was mixed with a relatively large amount of the stable iodine isotope .(carrier) , which competed with the radioactive form for utilization. It was not possible to administer much radioactive material without at the same time using quantities of stable isotope larger than the individual's normal daily requirement of this element. In this case, thyroid behavior might have been complicated by an iodine effect. Furthermore, with the small amounts of radioactivity used, quantitative measurements in vivo were not entirely satisfactory. Later, carrier-free radioactive iodine became available, and its use circumvented these earlier difficulties. With this material, considerable radioactivity is carried by very minute amounts of iodine, so that the quantity of the element administered is much smaller than the normal daily intake. Tracer studies have been carried out with this material in various institutions, to determine uptake and excretion in normal individuals and those suffering from thyroid disorders (4, 5, 6, 13). These investigations showed that in the normal subjects, within twenty-four hours, about 20 per cent of the administered material is in the gland, and most of the rest has been excreted by the kidneys. In toxic goiter, the glandular uptake is two to four times that in the normal. In view of these findings, it appeared that radioactive iodine might be used to deliver an internal radiation therapy to the hyperactive gland. As the radioactive atoms disintegrate, they emit beta and gamma rays, producing the same type of tissue reaction as x-rays, but with the difference that the irradiation is markedly localized in the gland itself. This is in contrast to the much larger volume of tissue necessarily irradiated when x-rays are used. The amount of radiation delivered into the gland depends on the amount of isotope deposited there, its half-life, and the type of radiation it emits. Two isotopes of iodine are suitable for attempting this type of therapy: I130, with a half-life of 12.6 hours, and p3r, with a half-life of eight days. The latter was not readily produced until recently, but the fomer became available in a few localities about 1943, and two groups in Boston employed it for therapeutic purposes in toxic goiter (7, 8). Results obtained in other clinics have not yet been reported. Since the release of isotopes from the pile at Oak Ridge, it has been possible for suitably equipped institutions to obtain I131.2 Accordingly an appraisal of the treatment of toxic goiter with this agent has been undertaken in several hospitals. The study here reported was begun in October 1946; the material is presented as a preliminary report.