Efficacy of Low-dose and High-dose Radioactive Iodine Ablation With rhTSH in Korean Patients With Differentiated Thyroid Carcinoma: The First Report in Nonwestern Countries.

OBJECTIVE: The aim of this study was to confirm the equivalent efficacy of recombinant human TSH (rhTSH) and thyroid hormone withdrawal (THW) as used in the preparation for low-dose and high-dose radioactive iodine (RAI) ablation in Korean patients with differentiated thyroid carcinoma. SUBJECTS AND METHODS: This retrospective study was designed to compare the efficacy of rhTSH and THW when used before ablation with low-dose (30 mCi) and high-dose (100 mCi) RAI, respectively. The study group included 570 patients with DTC with tumors staged T1 to T3, N0 to N1, and M0. Before RAI ablation, 190 patients used rhTSH and 380 patients matched by age, sex, T-stage, and N-stage used THW. The success of ablation was evaluated in each group based on 4 criteria: (1) stimulated thyroglobulin (sTg) <2 ng/mL, (2) sTg<2 ng/mL and negative diagnostic whole-body scan (DxWBS), (3) sTg<1 ng/mL, and (4) sTg<1 ng/mL and negative DxWBS. RESULTS: When both sTg<2 ng/mL and negative DxWBS were selected as criteria for success in patients treated with low-dose RAI, the success rates were 80.5% and 77.0% with rhTSH and THW, respectively (95% confidence interval, 5.9-12.8). Using both sTg<1 ng/mL and negative DxWBS as criteria, success rates were 78.2% and 71.8% with rhTSH and THW, respectively (95% confidence interval, 3.6-16.2). Using any criteria for success, low-dose RAI ablation with rhTSH was as effective as THW. Similar results were found for high-dose RAI ablation in patients using either rhTSH or THW. CONCLUSIONS: Low-dose and high-dose RAI ablation were equally effective using either rhTSH or THW before ablation in Korean patients with DTC, respectively.

The impact of iodinated contrast agent administered during preoperative computed tomography scan on body iodine pool in patients with differentiated thyroid cancer preparing for radioactive iodine treatment.

BACKGROUND: Iodine in iodinated contrast agents (ICAs) interferes with radioactive iodine treatment (RAIT) and diagnostic scans in patients with differentiated thyroid carcinoma (DTC) because it can compete with ¹³¹I. Published guidelines recommend delaying RAIT for three to four months in patients who have been exposed to ICA. Spot urinary iodine concentration is a useful marker to reflect the body iodine pool. We investigated the impact of ICAs administered at preoperative computed tomography (CT) scan on the body iodine pool to determine the proper time interval between preoperative CT and RAIT in DTC patients. METHODS: We performed a retrospective review of 1023 patients with DTC who underwent a preoperative CT scan with ICA, total thyroidectomy, and one week of low-iodine diet in preparation for RAIT. Urine iodine excretion (UIE) was measured in spot urine by inductively coupled plasma mass spectrometry and reported both in simple concentration (µg/L) and divided by gram creatinine (µg/gCr). Patients were divided into five groups by time interval in days between preoperative CT scan and spot urine iodine measurement (A, 31-60 [n=29]; B, 61-90 [n=155]; C, 91-120 [n=546]; D, 121-150 [n=226]; E, 151-180 [n=67]). RESULTS: The median (interquartile range) of UIE (µg/gCr) in each group was 44.4 (27.7-73.2) in group A, 33.3 (22.8-64.7) in group B, 32.7 (20.8-63.0) in group C, 32.0 (20.6-67.0) in group D, and 30.4 (19.6-70.8) in group E. There was no significant difference between group A and the remaining groups (p>0.05) Also, the proportion of patients who achieved the appropriate UIE for RAIT according to our hospital's cutoff (≤66.2 µg/gCr) was not different between groups (A, 72.4%; B, 76.1%; C, 77.5%; D, 74.8%; E, 74.6%) (p=0.78). CONCLUSION: This study shows that a UIE of one month after preoperative CT scan with ICA was not higher than that of six months after CT scan in patients who underwent total thyroidectomy for DTC. Thus, current guidelines that recommend delay of RAIT for three to four months after CT scan with ICA should be revisited and future studies to clarify the appropriate time interval between CT scan with ICA and RAIT are warranted.