Clinical trial of different doses of 131-I in treatment of thyrotoxicosis.

Abstract

Radioactive iodine, principally 131I, has been widely used for the treatment of thyrotoxicosis for over 15 years. This method has many advantages, particularly that it causes no discomfort to the patient, does not require admission to hospital, and a recurrence of thyrotoxicosis is rare. At first the main concern was that the irradiation might induce malignant disease, but the evidence to date suggests that the hazard is negligible, parti cularly if 131I therapy is confined to the older age groups. The irradiation dose to the bone marrow is low, and the subsequent incidence of leukaemia is not significantly greater than that in the general population (Pochin, 1960, 1964 ; Green et al., 1961). Thyroid neoplasms may follow irradiation of the thyroid in infancy and childhood, and cases have been reported after the use of 131I for the treatment of thyrotoxicosis in children (Sheline et al., 1962 ; Karlan et al., 1964 ; Kogut et al., 1965). Two cases of thyroid carcinoma have been reported after 131I therapy of thyrotoxicosis in adults, but in both instances the carcinoma was probably present when the radioiodine was administered (Kilpatrick et al., 1957 ; Staffurth, 1966). Two definite disadvantages of 131I therapy have emerged? namely, delay in controlling the hyperthyroidism and sub sequently a rising incidence of hypothyroidism. These features have been stressed in several reports (Beling and Einhorn, 1961 ; Green and Wilson, 1964 ; Dunn and Chapman, 1964 ; Nofal et al., 1966 ; Greig et al., 1966). In some retrospective surveys of the results of 131I therapy no relation could be established between the method of determining the dose of radioactive iodine and the subsequent development of hypothyroidism (Macgregor, 1963). However, examination of the results reported by Green and Wilson (1964), and of experiments on thyroid cell survival after irradiation (Al-Hindawi and Wilson, 1965), suggested that the increasing incidence of hypothyroidism with the passage of time was probably related to the dose. In these circumstances it was thought both justifiable and important to carry out a prospective clinical trial to clarify the effects of different doses of 131I in the treatment of thyro toxicosis. A preliminary report of this work has been published (Smith and Wilson, 1965).