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This document provides the new EANM guideline on radioiodine therapy of benign thyroid disease. Its aim is to guide nuclear medicine physicians, endocrinologists, and practitioners in the selection of patients for radioiodine therapy. Its recommendations on patients' preparation, empiric and dosimetric therapeutic approaches, applied radioiodine activity, radiation protection requirements, and patients follow-up after administration of radioiodine therapy are extensively discussed., (© 2023. The Author(s).)

The EANM Dosimetry Committee Series "Standard Operational Procedures for Pre-Therapeutic Dosimetry" (SOP) provides advice to scientists and clinicians on how to perform patient-specific absorbed dose assessments. This particular SOP describes how to tailor the therapeutic activity to be administered for radioiodine therapy of benign thyroid diseases such as Graves' disease or hyperthyroidism. Pretherapeutic dosimetry is based on the assessment of the individual (131)I kinetics in the target tissue after the administration of a tracer activity. The present SOP makes proposals on the equipment to be used and guides the user through the measurements. Time schedules for the measurement of the fractional (131)I uptake in the diseased tissue are recommended and it is shown how to calculate from these datasets the therapeutic activity necessary to administer a predefined target dose in the subsequent therapy. Potential sources of error are pointed out and the inherent uncertainties of the procedures depending on the number of measurements are discussed. The theoretical background and the derivation of the listed equations from compartment models of the iodine kinetics are explained in a supplementary file published online only.

Purpose: A considerable amount of radioiodine is exhaled after radioiodine therapy leading to unwanted radiation exposure through inhalation. This study focused on the concentration of radioactivity exhaled and its chemical nature., Methods: Air exhaled by 47 patients receiving (131)I-iodine for different thyroid diseases (toxic goitre n = 26, Graves' disease n = 13, thyroid cancer n = 8) was investigated with a portable constant air-flow sampler. Different chemical iodine species were collected separately (organic, elemental and aerosolic) up to 26 h after administration of the radioiodine capsule. The data approximated to a monoexponential time-activity curve when integrated over 100 h. The radioactivity in the filters was measured with a well counter at defined time points after administration., Results: The radioactivity of (131)I in the exhaled air 1 h after administration ranged from 1 to 100 kBq/m(3). Two parameters (half-life of radioiodine exhalation and time-integrated activity over 100 h) were substantially higher in patients with cancer after near-total thyroidectomy (11.8 ± 2.1 h and 535 ± 140 kBq / m(3), respectively) than in patients with hyperfunctioning thyroid tissue due to toxic adenoma (7.6 ± 2.5 h and 115 ± 27 kBq / m(3), respectively) or Graves' disease (6.4 ± 3.6 h and 113 ± 38 kBq / m(3), respectively). The percentage of radioiodine in the exhaled air in relation to radioiodine administered to the patient was between 80 ppm and 150 ppm. The fraction of organically bound radioiodine (mean value) for all time points after administration was 94-99.9%. This percentage did not depend on the type of thyroid disease., Conclusion: The amount of exhaled radioiodine is small but by no means negligible on the first day after administration. This is the first study to provide experimental evidence on a systematic basis that radioiodine becomes exhalable in vivo, i.e. in the patient. The mechanism of organification of orally administered radioiodine remains to be investigated.

The purpose of the present guidelines on the (131)I therapy of benign thyroid disorders formulated by the European Association of Nuclear Medicine (EANM) Therapy Committee is to provide advice to nuclear medicine clinicians on how to treat benign thyroid conditions employing optimal (131)I activities. The recommendations were formulated based on recent literature and expert opinion regarding rationale, indications and contraindications for the use of (131)I procedures, as well as the adequate (131)I activities in different thyroid disorders, and the administration and patient preparation techniques to be used. Recommendations are also provided on history and examinations before (131)I therapy, patient counselling and precautions associated with (131)I therapy. Furthermore, potential side effects and alternative treatment modalities are reviewed. Special attention is paid to these aspects in the treatment of children undergoing this procedure.