Short-Term Effectiveness of Low-Dose Radioiodine Ablative Treatment of Thyroid Remnants After Thyroidectomy for Differentiated Thyroid Cancer

Abstract

Twenty-five patients from a marginally iodine-deficient area with differentiated thyroid cancer who were referred to our unit between 1991 and 1997 had a residual thyroid uptake (RTU) at 24 hours of 5% or more after surgery. None of them underwent reoperation: 8 of 25 had RTU between 5% and 10% and were considered at low risk for both local recurrences and/or distant metastases; 17 of 25 had RTU greater than 10% and up to 30% and refused re-intervention. After detection of their cervical uptake by using a ¹³¹I tracer dose of 3.7 MBq (100 μCi), all 25 were treated with 1110 MBq (30 mCi) of ¹³¹I. A whole-body scan (WBS) performed 5 days later revealed ¹³¹I uptake corresponding to metastatic lymph nodes in the anterior part of the neck in 1 patient and the persistence of only RTU in 24 of 25 patients. RTU and thyroglobulin (Tg) levels were reevaluated 6 months later in all patients and compared to preradioiodine treatment values. RTU, ranging at presentation between 5% and 30%, decreased to below 1% in all but one patient. Serum Tg values, ranging between 1.6 and 108 ng/mL before radioiodine treatment, decreased to below 1.6 ng/mL in all but 4 of them (whose serum Tg was between 2 and 3.4 ng/mL). Our data indicate that 1,110 MBq of ¹³¹I can permit complete ablation of 80% of thyroid remnants concentrating up to 30% of radioiodine activity. A relation between this high success rate and iodine deficiency can be hypothesized because an increasing uptake of radioiodine by thyroid remnants could result in overestimation of their size. Therefore, our observations suggest that in iodine deficient areas, a hasty decision to carry out complete thyroidectomy should be avoided, even in the case of thyroid remnants with RTU up to 30%.