Comparison of two different types of treatment approaches using I131 for benign pathologies of the thyroid

Introduction: The main etiologies of hyperthyroidism are: Graves' disease, toxic nodule and toxic nodular goiter. The management of hyperthyroidism is varied, including synthetic antithyroid drugs, ablative surgery and radioiodine therapy. The incorporation of the radioiodine in the thyroid cells is variable from one patient to the other, for physiological and dietary reasons, but also related to different etiologies of hyperthyroidism. Mainly, two approaches are widely used to treat hyperthyroidism with radioiodine (131I): a- the fixed dose approach and b- Dosimetry based approach.

Aim: To compare the efficacy to control hyperthyroidism of two different radioiodine therapy protocols.

Methods: This retrospective study was approved by the Ethics Committee of our hospital. Were included patients referred for radioiodine therapy at the nuclear medicine department of CHU St Pierre, Brussels from January 1^th 2015 to December 31^th 2017. Two groups of patients were evaluated. Those who were treated with a fixed activity approach group and those who were treated applying a dosimetry based approach group. The administered 131I activity in the group of dosimetry-based group was calculated per the following formula’s: A- For hyperthyroidism related to toxic nodules : Calculated activity = 9250 kBq [asterisk] NW) / 24 hr RAIU (%). (NW: estimated nodule weight in grams. 24 hr RIU: % of 24 hours radioiodine uptake) B- For hyperthyroidism related to Grave’s disease: Calculated activity= x kBq [asterisk] W / 24 hr RIU (%). (x: estimated from a scale based on the weight of the gland. W: estimated thyroid weight in grams. 24 hr RIU: % of 24 hours radioiodine uptake) Success of radioiodine therapy was defined as clinically/biochemically euthyroid/hypothyroid status after 6 months of I131 therapy without the need for other anti-thyroid therapy.

Results: 59 patients received radioiodine therapy for benign pathologies, 32 using fixed I131 activity administration and 27 patients have received I131 activity calculated using a dosimetry-based approach. The median activity was 229.77 ± 95.83 MBq in the fixed activity group and 236.06 ± 80.66 MBq in dosimetry based approach group (p: NS). At 6 months after treatment, in the fixed dose group, 6 patients persisted with low levels of Thyroid Stimulating Hormone (TSH), 18 were euthyroid, and 4 were hypothyroid. Success rate was 69%. In the dosimetry-based approach group, 3 patients persists showing hyperthyroidism, 20 were euthyroid, and 3 were hypothyroid. Success rate was 85%. Concerning the treatment success rate, there was no statistically significant difference (p=0.22) between the two groups (using Fisher’s Exact test). We had performed a subgroup analysis, comparing the two treatment approaches for each different benign thyroid pathologies treated, we did not found neither any statistical significant difference (Toxic nodule p=0.13; Grave’s disease, p=0.33; Toxic nodular goiter, p=0.54.

Conclusions: We found comparable results concerning the success rates of the two treatment approaches. However prospective studies with a longer follow-up and large number of patients are necessary to confirm these results.

• Download figure
• Open in new tab
• Download powerpoint