Clinical Outcome of Remnant Thyroid Ablation with Low Dose Radioiodine in Korean Patients with Low to Intermediate-risk Thyroid Cancer

Abstract

Radioiodine activity required for remnant thyroid ablation is of great concern, to avoid unnecessary exposure to radiation and minimize adverse effects. We investigated clinical outcomes of remnant thyroid ablation with a low radioiodine activity in Korean patients with low to intermediate-risk thyroid cancer. For remnant thyroid ablation, 176 patients received radioiodine of 1.1 GBq, under a standard thyroid hormone withdrawal and a low iodine diet protocol. Serum levels of thyroid stimulating hormone stimulated thyroglobulin (off-Tg) and thyroglobulin-antibody (Tg-Ab), and a post-therapy whole body scan (RxWBS) were evaluated. Completion of remnant ablation was considered when there was no visible uptake on RxWBS and undetectable off-Tg (<1.0 ng/mL). Various factors including age, off-Tg, and histopathology were analyzed to predict ablation success rates. Of 176 patients, 68.8% (n = 121) who achieved successful remnant ablation were classified into Group A, and the remaining 55 were classified into Group B. Group A presented with significantly lower off-Tg at the first radioiodine administration (pre-ablative Tg) than those of Group B (1.2 ± 2.3 ng/mL vs. 6.2 ± 15.2 ng/mL, P = 0.027). Pre-ablative Tg was the only significant factor related with ablation success rates. Diagnostic performances of pre-ablative Tg < 10.0 ng/mL were sensitivity of 99.1%, specificity of 14.0%, positive predictive value of 71.1%, and negative predictive value of 87.5%, respectively. Single administration of low radioiodine activity could be sufficient for remnant thyroid ablation in patients with low to intermediate-risk thyroid cancer. Pre-ablative Tg with cutoff value of 10.0 ng/mL is a promising factor to predict successful remnant ablation.Graphical Abstract

Efficacy and Affecting Factors of 131I Thyroid Remnant Ablation After Surgical Treatment of Differentiated Thyroid Carcinoma

“…The success rate of the first 131 I ablation after surgical treatment of DTC varies in the published literature, and its affecting factors are not well defined. Previous studies report that the success rates of the first 131 I thyroid remnant ablation range from 43 to 87.2% (13–16), and some factors could possibly affect the therapeutic effectiveness, such as patient gender, surgery type, size of residual thyroid tissue, tumor size, TSH level, and thyroglobulin level (17–19). Considering the age range of this study population (8–79 years), to rule out the effect of age difference on the success rate of 131 I ablation, we compare the success rates between the aged ≤18 years (children and adolescents) group and >18 years old (adults) group and between the group aged <45 years old and ≥45 years old group.…”

Determining patient selection tool and response predictor for outpatient 30 mCi radioiodine ablation dose in non-metastatic differentiated thyroid carcinoma: a Japanese perspective

“…A Canadian study (n = 193, low to intermediate risk patients) revealed that pre-ablation Tg level cut-off of 6 ng/mL was predictive of 30 mCi RAI ablation response [33], while a Brazilian study (n = 237, low to intermediate risk patients) reported 10 ng/mL [34] which later included in their national consensus [35]. A Korean study (n = 176, low to intermediate risk patients), also indicated that 10 ng/mL cut-off was useful to predict response to 30 mCi RAI ablation [36], which was of particular interest since both Korean and Japanese are similar in their iodine-rich the dietary status [37].…”

“…As concluded in many studies, age was not a predictive factor for 30 mCi RAI ablation [33,36]. However, American and European consensus determine 45 years old as the risk limit in a long-term outcome [5,15].…”

Factors Associated with Dose Determination of Radioactive Iodine Therapy for Differentiated Thyroid Cancer

“…Multiple studies showed that postoperative TSH-stimulated Tg is related to risk of recurrence [50,51]. Elevated postoperative Tg levels are also related to ablation failure after 1.1 GBq of RAI administration [60].…”