Endocrine Abstracts

Introduction: Radioiodine (RAI) has been used for the treatment of Graves’ hyperthyroidism since 1940s. It is relatively safe and considered as one of the definitive therapies. Achievement of hypothyroidism or euthyroidism is defined as a successful therapy.

Methods: The study was conducted in 366 patients (80.60% of women) with Graves’ disease (GD), aged 46.76±13.52 years. We analyzed retrospectively hormonal and imaging findings (scintigraphy, ultrasonography), including isotopic results in subjects treated at Department of Nuclear Medicine and Endocrinology Department during the eight-year period. The efficacy of RAI therapy has been assessed based on free thyroid hormones levels, measured 12 months after radioiodine administration.

Results: Mean concentrations of thyroid hormones before therapy were: FT4-38.40±22.17 (12.0–22.0 pmol/l) and FT3-21.9±17.11 (3.0–7.0 pmol/l). The thyroid mass was estimated to be 69.67±38.87 g. Mean RAI 24-h uptake was 63.93±16.15% and therapeutic activity of RAI, calculated using Marinelli’s formula, was 544.28±176.35 MBq. The used thyroid-absorbed doses of RAI (Gy) were: ≤120, >120 and ≤150, >150 (49.18% vs 46.99% vs 3.83% of subjects with GD, respectively). After RAI therapy, hypothyroidism was found in 39.34% GD participants (39.34% of F; 39.44% of M), euthyreosis - in 24.32% (25.42% of F; 19.72% of M) and hyperthyroidism – in 36.34% (35.26% of F; 40.84% of M). The efficacy of RAI therapy was achieved in 63.66% of patients (F–64.75%; M-59.15%). An effective cure of hyperthyroidism was significantly correlated with lower: thyroid mass (59.35±33.26g vs 87.75±41.43g; P=0.000), RAI 24-h uptake (62.64±16.54% vs 66.20±15.21%; P=0.042) and, surprisingly, administered dose (519.25±180.16MBq vs 588.12±175.63MBq; P=0.000). No significant associations between successful therapy and patients’ age, levels of free thyroid hormones before therapy and thyroid absorbed dose were found.

Conclusions: RAI therapy was effective in 63.66% of patients with GD. Females responded better to treatment than males. The cure correlated with thyroid mass, RAI 24-h uptake and dose of radioiodine.