Endocrine Abstracts

In PTC, radioiodine required dose for thyroid remnant ablation is uncertain. Recent works show that low doses may be sufficient for low risk patients.

Aim: To evaluate the efficacy and safety of thyroid remnant ablation in patients with low-risk PTC by using 1100 MBq (30 mCi) outpatient doses.

Materials and methods: Twenty-five patients (24 women, 55 years-old mean age, range 34–77) referred for ablation of postsurgical thyroid remnants diagnosed with low-risk PTC (pT1-T2, N0, M0) were studied. After total thyroidectomy, an outpatient ablation was performed with 1100 MBq of ¹³¹I under rhTSH stimulation with strict radiation protection measurements and dosimetry control at home environment. Whole body scan (WBS) and SPECT-CT were performed on the fifth day. Control of therapeutic efficacy was performed at 6 months, using WBS and SPECT-CT with ¹²³I after stimulation with rhTSH. Basal and post-stimulated thyroglobulin levels were determined in both studies. Ablation was considered successful when no abnormal activity was observed in WBS and SPECT-CTs and when basal/stimulated thyroglobulin levels were under 1 and 2 ng/ml, respectively.

Results: All 25 patients showed thyroid uptake without uptaking adenopathies in the WBS and SPECT-CTs performed on the fifth day after administration of ¹³¹I. In 23/25 patients (92%) a successful ablation at 6-month efficacy control was achieved. One patient (5.1 ng/ml stimulated Tg) was re-treated with a new dose of 30 mCi and a second patient (2.3 ng/ml stimulated Tg) spontaneously normalised her basal and stimulated Tg levels at the 18-month control. Dosimetry on family members showed exposure levels of <0.2 mSv.

Conclusion: The postsurgical outpatient treatment with an activity of 1100 MBq is safe for the family environment and cost-effective in a great majority of patients with low-risk PTC.