No adverse affect in clinical outcome using low pre-ablation diagnostic (131)I activity in differentiated thyroid cancer: refuting thyroid stunning effect.

Abstract

Context Published studies of thyroid stunning due to pre-ablation (131)I scanning in the treatment of differentiated thyroid cancer (DTC) following thyroidectomy had shown inconsistent clinical impact. Objective To evaluate the clinical outcome in patients who were given a low diagnostic (131)I activity (1.1mCi or 40MBq) 6 days prior to radioiodine ablation (RAI). Design/setting Two cohorts of patients treated in a cancer referral center in 2004-2011. The eligibility criteria were 1) diagnosis of differentiated thyroid carcinoma (DTC); 2) total or near total thyroidectomy; 3) no distant metastasis; 4) received ≥82.4mCi (3050MBq) therapeutic (131)I activity. Patients/Interventions 305 consecutive patients treated in 2004-2008 (group A) had a diagnostic activity 1.1mCi of (131)I prior to RAI. The second cohort treated in 2009-2011(group B) consisted of 237 patients who did not undergo diagnostic (131)I scanning prior to RAI. Main outcome measures The tumor recurrence rate at 3 years and quantitative assessment using diagnostic radioiodine scans (DxWBS) and TSH-stimulated thyroglobulin (Tg) levels at 3-12 months post RAI. Results The 3-year recurrence free survival rate were 96.4% in both groups with 4.3% in group A and 3.4% in group B had tumor recurrence (p=0.91). The ablation success rates measured by DxWBS were 97.6% and 100% and by stimulated Tg were 85.3% and 85.8% in group A and B respectively (p=0.62). Conclusions The use of low diagnostic (131)I activity (1.1mCi) given 6 days prior to RAI was safe and convenient without adversely affecting the long term clinical outcome.