Radioiodine therapy for Graves disease: thyroid absorbed dose of 300 Gy-tuning the target for therapy planning

[Guideline for Radioiodine Therapy for Benign Thyroid Diseases (6/2022 - AWMF No. 031-003)]

This version of the guideline for radioiodine therapy of benign thyroid disorders is an update of the version, which was published by the German Society of Nuclear Medicine (Deutsche Gesellschaft für Nuklearmedizin, DGN) in co-ordination with the German Society of Endocrinology (Deutsche Gesellschaft für Endokrinologie, DGE, Sektion Schilddrüse) and the German Society of General- and Visceral-Surgery (Deutsche Gesellschaft für Allgemein- und Viszeralchirurgie, DGAV) in 2015. This guideline was harmonized with the recommendations of the European Association of Nuclear Medicine (EANM). According to the German "Directive on Radiation Protection in Medicine" the physician specialised in nuclear medicine ("Fachkunde in der Therapie mit offenen radioaktiven Stoffen") is responsible for the justification to treat with radioiodine. Therefore, relevant medical indications for radioiodine therapy and alternative therapeutic options are discussed within the guideline. This procedure guideline is developed in the consensus of an expert group. This fulfils the level S1 (first step) within the German classification of Clinical Practice Guidelines.

The EANM guideline on radioiodine therapy of benign thyroid disease

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.

[Radioiodine therapy for benign thyroid diseases (version 5). German Guideline]

The version 5 of the guideline for radioiodine therapy of benign thyroid disorders is an update of the version 4, which was published by the German Society of Nuclear Medicine (Deutsche Gesellschaft für Nuklearmedizin, DGN) in co-ordination with the German Society of Endocrinology (Deutsche Gesellschaft für Endokrinologie, DGE, Sektion Schilddrüse) and the German Society of General- and Visceral-Surgery (Deutsche Gesellschaft für Allgemein- und Viszeralchirurgie, DGAV) in 2007. This guideline was harmonized with the recommendations of the European Association of Nuclear Medicine (EANM). According to the German "Directive on Radiation Protection in Medicine" the physician specialised in nuclear medicine ("Fachkunde in der Therapie mit offenen radioaktiven Stoffen") is responsible for the justfication to treat with radioiodine. Therefore, relevant medical indications for radioiodine therapy and alternative therapeutic options are discussed within the guideline. This procedure guideline is developed in the consensus of a representative expert group. This fulfils the level S1 (first step) within the German classification of Clinical Practice Guidelines.

Radiation Safety Precautions in (131)I Therapy of Graves' Disease Based on Actual Biokinetic Measurements

CONTEXT

Radiation protection is an integral part of targeted radionuclide therapy. How to offer rational radiation precautions to patients with Graves' disease (GD) undergoing (131)I therapy is still a matter of ongoing discussions.

OBJECTIVE

The objective of the study was to formulate radiation precautions for GD patients undergoing (131)I therapy through actual biokinetic measurements for a particular population of patients.

DESIGN

This was a prospective study.

SETTING

The study was conducted at a university hospital.

PATIENTS

From January 2009 through January 2012, consecutive GD patients prepared for (131)I therapy were prospectively recruited.

MAIN OUTCOME MEASURES

Pretherapy thyroid radioiodine uptake and uptake ratio (4 to 24 h radioiodine uptake) were measured. Serial whole-body dose-rate measurements after therapy were performed to deduce (131)I whole-body retention. Calculations based on deduced whole-body retention and measured thyroid radioiodine biokinetics were derived to determine the thyroidal and extrathyroidal compartment uptake fractions and effective half-lives. Precaution times necessary to avoid close contact with family members and the general public were derived from these parameters and regulatory dose limits.

RESULTS

A total of 72 patients were eligible for the analysis. A high interpatient variability in (131)I biokinetics was observed: the mean peaking (131)I uptake (±1 SD) in the thyroid was 68% (±19%), and the range was 18%-89%; the mean effective (131)I half-life (±1 SD) in the remainder of the body was 5.1 (±0.9) hours (range 3.5-7.2 h). The mean measured initial dose rate (±1 SD) at 1.0 m after (131)I administration was 0.039 (±0.003) μSv·h(-1) · MBq(-1) (range 0.017-0.055 μSv·h(-1) · MBq(-1)). The 0.3:1.0 m initial dose rate ranged from 2.9 to 7.1, which was greatly lower than the projected ratio of 11.1 by the inverse square law approximation. On the basis of the measured radioiodine biokinetics and dose rates, detailed instructions were provided to limit nearby individuals' exposure.

CONCLUSION

The use of actual biokinetic measurements may remove the effect of variability errors associated with general default assumptions about the (131)I biokinetics in GD patients. The marked variability in (131)I biokinetics among GD patients reinforces the need for patient-specific iodine biokinetic measurements for radiation safety precautions.