Cure Rates After a Single Dose of Radioactive Iodine to Treat Hyperthyroidism: The Fixed-Dose Regimen

Abstract

IntroductionRadioactive iodine (RAI) has been used to treat hyperthyroidism for more than 70 years. Cure rates after RAI therapy range between 80% and 100%, with some patients requiring two or more doses. There is continued debate over which dosing regimen is optimal. We evaluated our cure rates after giving a single dose of radioactive iodine to treat hyperthyroidism using the fixed-dose regimen as opposed to the calculated-dose regimen. Materials and methodsWe retrospectively reviewed the clinical records of patients who had received their first single dose of RAI between 2016 and 2021. The patients had clinical and biochemical assessments every six weeks until six months post-RAI therapy, then every three months thereafter, if still not cured. Patients were deemed cured if they developed persistent hypothyroidism or euthyroidism after a single dose of RAI. The data included baseline demographics, adverse events, and cure rates after RAI treatment. ResultsOne hundred and thirty-eight patients received their first dose of RAI during the study period. Their mean ± standard deviation (SD) age was 56.9 ± 15.3 years, and there were 101 women and 37 men. The median duration of hyperthyroidism was 34 months, and 62% of the cases were affected by Graves' disease. A majority of patients (90%) were on an antithyroid drug prior to RAI therapy. The median (interquartile range) dose of RAI received by the group was 559 (546-577) megabecquerels (MBq). Four patients (2.9%) reported adverse events shortly after receiving RAI. Our overall cure rate was 87.7% amongst patients who received a single dose of RAI therapy. This number consisted of 96 patients (69.6%) who developed hypothyroidism and 25 patients (18.1%) who remained euthyroid. Our one-year cure rate was 84.1%. Further analysis revealed that women had a greater cure rate than men over the study period (92% vs 75.7%, p = 0.017). ConclusionWe have evaluated cure rates after a single dose of RAI therapy for the treatment of hyperthyroidism at our center. Our results are comparable to those reported at other centers using a similar dosing regimen.

Factors affecting timing of hypothyroidism following radioactive iodine therapy (RAIT) for patients with Graves’ disease: A 12-month observational study

“…Considering both euthyroidism and hypothyroidism success of RAIT, our study found that we achieved a success rate of 80.5% at 6 months after treatment, which further increased to 87.5% after 12 months. Murthy et al [20], and Madu et al [21], had success rates align closely to our study with 85.3 and 87.5% successfully treated within 6 months and 93.2% within 1 year On Ekkasit et al [22], reported a success rate of only 59.6% after a single radioiodine dose.…”

Use of a dosimetry‐based RAI protocol for treatment of benign hyperthyroidism optimises response while minimising exposure to ionising radiation

“…The dosimetry protocol executed in this study in a busy tertiary centre achieved success rates of 84% for a combined cohort of GD and TMNG, successfully facilitating reduced radiation exposure in 44%. Success rates were not affected by treatment modality used and are comparable to outcomes published in response to higher fixed activities 9,14 …”

“…Success rates were not affected by treatment modality used and are comparable to outcomes published in response to higher fixed activities. 9,14 In GD successful treatment is aligned with a greater absorbed thyroid dose. 30 However, a meta-analysis of the relationship between the radiation absorbed dose to the thyroid and treatment response confirmed this relationship plateaus at an absorbed dose to the thyroid of 300 Gy.…”

“…The European Thyroid Association guideline in 2018 does not specify but comments it remains fully acceptable to offer fixed activities of RAI as 'no dose calculation can secure long‐term euthyroidism' 13 . Therefore activities between 500 and 700 MBq are commonplace in clinical practise with observed success rates post single treatments in the literature between 80 to 95% 4,14 . In our institution an internal review of practise carried out in 2019 demonstrating cure rates of 87.5% for GD and TMNG served as justification for using a lower fixed activity of 200MBq and 400MBq respectively 15 .…”

“…13 Therefore activities between 500 and 700 MBq are commonplace in clinical practise with observed success rates post single treatments in the literature between 80 to 95%. 4,14 In our institution an internal review of practise carried out in 2019 demonstrating cure rates of 87.5% for GD and TMNG served as justification for using a lower fixed activity of 200MBq and 400MBq respectively. 15 Supporting this approach NICE guidelines in 2019 specified that the RAI dose should be minimised, but further research is required comparing dosimetry to fixed activities before specifying how this should be achieved.…”