A Systematic Review and Meta-Analysis of the Relationship Between the Radiation Absorbed Dose to the Thyroid and Response in Patients Treated with Radioiodine for Graves' Disease

Background: Patients with Graves' disease are commonly treated with radioiodine. There remains controversy over whether the aim of treatment should be to achieve euthyroidism or hypothyroidism, and whether treatments should be administered with standard levels of radioactivity or personalized according to the radiation absorbed doses delivered to the thyroid. The aim of this review was to investigate whether a relationship exists between radiation absorbed dose and treatment outcome. Methods: A systematic review and meta-analysis of all reports published before February 13, 2020, were performed using PubMed, Web of Science, OVID MEDLINE, and Embase. Proportion of patients achieving nonhyperthyroid status was the primary outcome. Secondary outcomes were proportion of patients who were specifically euthyroid or hypothyroid. A random-effects meta-analysis of proportions was performed for primary and secondary outcomes, and the impact of the radiation absorbed dose on treatment outcome was assessed through meta-regression. The study is registered with PROSPERO (CRD42020175010). Results: A total of 1122 studies were identified of which 15, comprising 2303 Graves' disease patients, were eligible for the meta-analysis. A strong association was found between radiation absorbed dose and nonhyperthyroid and hypothyroid outcomes (odds ratio [OR] = 1.11 [95% confidence interval {CI} 1.08–1.14] and OR = 1.09 [CI 1.06–1.12] per 10 Gy increase). Higher rates of euthyroid outcome were found for radiation absorbed doses within the range 120–180 Gy when compared with outside this range (n = 1172, OR = 2.50 [CI 1.17–5.35], p = 0.018). A maximum euthyroid response of 38% was identified at a radiation absorbed dose of 128 Gy. Conclusions: The presented radiation absorbed dose–response relationships can facilitate personalized treatment planning for radioiodine treatment of patients with Graves' disease. Further studies are required to determine how patient-specific covariates can inform personalized treatments.