Abstract
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Objectives The purpose of this study is to evaluate whether immediate change of serum thyroglobulin (Tg) level after radioiodine therapy can be a predictive factor for ablation of residual thyroid or metastatic lesion.
Methods 29 patients performed radioiodine therapy, and measured serum Tg level immediately (post 4 days) after (RAI) therapy and following treatment (after 6-12 months). Thyroid function test parameters, Tg and TgAb were measured by radioimmunoassay kits. rTg (Immediate Tg/1st time stimulation Tg), dTg (Immediate Tg - 1st time stimulation Tg), rTgAb (Immediate TgAb/1st time stimulation TgAb) and dTgAb (Immediate TgAb - 1st time stimulation TgAb) were calculated. I-131 whole body scan parameters were rUptake (1-(2nd time therapy uptake ratio/1st time therapy uptake ratio)) and dUptake (1st time therapy uptake ratio - 2nd time therapy uptake ratio). Uptake (Lesion ROI uptake/Brain ROI uptake) was calculated according to geometric average of lesion in anterior and posterior images of I-131 whole body scan.
Results Positive correlation between rTg and rUptake was checked by Pearson’s correlation (correlation coefficient = 0.382, P=0.041). In subgroup analysis, rTg more than 1.5 reveals significantly high rUptake and dUptake (rUptake: 0.74±0.25 vs. 0.45±0.31, P=0.01). Moreover, rUptake more than 0.7 revealed high rTg with significance (rTg: 8.80±9.50 vs. 1.31±0.81, P=0.003).
Conclusions High ratio between immediate Tg and 1st time stimulation Tg reflects high ablation rate of residual or metastatic lesion after radioiodine therapy