Radiation Dose Boosts Efficacy of Radioactive Iodine in Graves Disease

The application of a high absorbed dose of 250 grays (Gy) in patients with Graves disease resulted in high efficacy of radioactive iodine (RAI) therapy at 1-year follow-up, according to a study published in Advances in Clinical and Experimental Medicine.

The results of RAI treatment for Graves disease are related to the choice of diagnostic and dosimetry protocols, the steroid protection used, and subsequent doses, the researchers explained, but the effect of a high tissue-absorbed dose on the level of antithyriod antibodies (ATA) “has rarely been considered.”

The prospective study was based on data collected in 2010 and included 46 consecutive patients (mean age, 47.4±13 years; range, 17-72 years; 38 women) with Graves disease and an increased serum concentration of antithyroid stimulating hormone (TSH) receptor thyrotropin receptor antibody (TRAb). Eight patients (17.4%) received 30 mg oral prednisone, starting 1 day before RAI therapy, which was continued for 56 consecutive days with tapering by 5 mg every 4 to 5 days.

The radioimmunoassay was used as a first-line therapy in 2 (4.3%) patients, a second-line therapy in 42 patients (91.4%), and a third-line therapy in 2 patients (4.3%). Antithyroid drugs were administered in pretreatment of 44 patients (95.7%).

The participants received a dose of 463.6±188.3 megabecquerel (MBq) (median, 400.3 [326.7-588.3] MBq; range:177.6-969.4 MBq). Successful RAI therapy outcome was defined as normal thyroid function or hypothyroidism.

The treatment was successful in 42 of the 46 patients (91.3%). Hypothyroidism occurred in 35 patients (76.1%), and normal thyroid function occurred in 7 patients (15.2%). Persistent hyperthyroidism occurred in 4 participants (8.7%).The rate of average reduction of thyroid volume after RAI therapy was 34.9%. For 7 patients (15.2%), no reduction occurred.

The researchers also found that a shorter effective half-life correlated with a higher baseline TRAb concentration and lower final anti-thyroid peroxidase (TPO) serum concentration (P =.03 and P =.01, respectively). Patients with steroid protection had lower final TRAb (P =.049), and those without steroid protection had significantly higher final anti-TPO concentration (P =.02), according to an intergroup comparison. Additionally, patients taking thyroid replacement therapy (TRT) showed significantly higher final anti-TPO concentration (P =.04) in an intergroup comparison.

The investigators noted the small sample size in their study and that their analysis lacked data on patients’ smoking habits before and after RAI as limitations to the study.

However, even with these limitations, researchers stated several conclusions. “The application of a high absorbed dose of 250 Gy in Graves disease resulted in high efficacy of RAI therapy at 1-year follow-up. An increased antithyroid antibody level and its relationships with effective half-life and thyroid volume reduction were [also] observed at 1-year follow-up, [and] there is a possible relationship between steroid protection and anti-TPO concentration.”

Reference

Listewnik MH, Piwowarska-Bilska H, Jasiakiewicz K, Birkenfeld B. Influence of high tissue-absorbed dose on antithyroid antibodies in radioiodine therapy of Graves’ disease patients. Adv Clin Exp Med. 2021;30(9):913-921.doi:10.17219/acem/137779