Studies with Radioiodine

Abstract

When tissues have been irradiated with I131 and are subsequently examined, any histologic changes almost inevitably will be considered to be, at least in part, the result of that irradiation. On the other hand, small amounts of radiation may cause no recognizable histologic effects. In the thyroid gland the effects of disease, of aging, and of drugs may be present in the tissues and may be attributed to the radiations from I131 rather than to the true causes. Such errors of interpretation may easily lead to an inaccurate description of the lesions induced by irradiation. This paper, consisting of four parts, presents the results of an investigation intended to detect changes in thyroid tissue due to radiations from I131 and to distinguish them from changes attributable to other causes. The first part is an account of four test-retest studies in which one of us (SL), a pathologist, attempted to distinguish irradiated from non-irradiated tissues by their histologic appearance; the second part is an analysis of the consistency and reliability of these interpretations, undertaken for the purpose of finding those sections of tissue which would show unmistakably the effects of irradiation. These tissues were then studied histologically and are carefully described in the third part. The fourth part considers the differentiation of those histologic characteristics which were attributed to irradiation from those due to other causes. I. Test-Retest Studies Materials and Methods The materials studied consisted of microscopic slides of thyroid tissue from 19 unirradiated patients and from 20 patients who had received radiation from I131.2 The sections of unirradiated tissues showed evidences of various thyroid diseases. Some of the glands had been subjected to the action of propylthiouracil and stable iodine in the form of Lugol's solution. Among the 20 sections of tissues that had been irradiated with I131,3 19 came from patients having toxic diffuse goiter and one came from a normal portion of the gland of a patient who had a thyroid carcinoma. Fifteen of the irradiated tissues had also been subjected to the action of propylthiouracil and/or stable iodine. After examination of the histologic section, the pathologist stated whether or not, in his opinion, the tissue showed evidence of having been irradiated. In studies of this kind, definitions of terms and description of procedures are of great importance. All the tissues showed various degrees of the effect of naturally occurring diseases of the thyroid4, treatment with drugs and agents other than irradiation, or of aging. For the purposes of the test-retest studies, the following meanings were adopted for negative, or non-irradiated (−), and positive, or irradiated (+).