Quantification of I-131 thyroid remnant uptake in patients with thyroid cancer.

Radioiodine ablation is commonly performed after thyroidectomy for well-differentiated thyroid cancer (DTC). This study aimed to quantify thyroid remnant uptake in standardized uptake values (SUV) and evaluate its correlation with post-therapy Thyroglobulin (Tg) levels across different risk groups. We retrospectively quantified SUV uptake with attenuation, scatter, and resolution recovery corrections on post-therapy SPECT/CT in thyroid cancer patients referred to our centre between 2015 and 2017. Thyroid remnant was segmented with a maximum SUV of 0.5 as the threshold and total thyroid remnant uptake (SUV) was obtained. Patients were stratified into low-intermediate, high-intermediate, and high-risk groups based on clinical risk and therapeutic dose. The primary outcome was the correlation between SUV and post-therapy Tg levels. The cohort consisted of 174 adults (age: 50.7±16.0 yr, F:M=110:64). Moderate correlations were found between SUV and Tg levels in low-intermediate and high-intermediate groups (Spearman's =0.65, P<0.001; =0.61, P<0.001, respectively). No significant correlation was found in the high-risk group (=0.12, P=0.33). Stimulated Tg levels increased (median Tg: 4, 7, and 13 pmol/L) and thyroid remnant uptake decreased (median SUV: 272, 51, and 33) across the low-intermediate, high-intermediate, and high risk groups. In conclusion, this study shows good correlations between the thyroid remnant uptake and thyroglobulin in subgroups of patients with low-intermediate and high-intermediate risk DTC. The rationales for lack of significant correlation in the high-risk group DTC were discussed. Thyroid uptake quantification may serve as a feasible substitute for Tg measurements in post-ablation follow-up, offering potential for predicting disease recurrence.