Analysis on the factors affecting the efficacy of 131Ⅰ remnant ablation in patients after thyroidectomy for differentiated thyroid carcinoma

Objective 131Ⅰ is the most effective treatment for thyroidal remnant ablation after thy-roidectomy in patients with differentiated thyroid carcinoma (DTC). Ways to improve its therapeutic efficacy have been a major clinical concern. This study was designed to assess the efficacy of thyroid ablation by finding out its leading factors. Methods Eighty cases of post-operative DTC patients who had undergone first 131Ⅰ remnant ablation therapy were retrospectively reviewed. The efficacy of the therapy was assessed by a diagnostic 131Ⅰ whole body follow-up scan 3- 6 months later. The ablation therapy was considered to be suc-cessful only if no conceivable radioactivity was detected in the thyroidectomy bed. The χ2 test and multi-vari-ance Binary Logistic regression were used to analyze 9 variances which might affect the therapeutic efficacy, including gender, age (<45 years and ≥45 years), type of pathology (papillary or follicular carcinoma), metastasis, residual thyroid weight (low, median, high), 24 h radioiodine uptake ratio (< 10%, 10%-20%, >20%), thyroglobulin (Tg, negative or positive), thyroid stimulating hormone (TSH, <30 mU/L, 30-60 mU/L, >60 mU/L), and radioiodine dose (<1850 MBq,1850-3700 MBq, >3700 MBq). Results 131Ⅰ remnant ablation therapy was successful in 58 of 80 DTC patients (72.5%). Three variances were found to have affected the therapeutic efficacy: residual thyroid weight, 24 h radioiodine uptake ratio and 131Ⅰ dose. The corresponding intra-groups statistical difference of those 3 variances was significant by χ2 test (χ2 = 8.892, 9.528, 15.085, P = 0.012, 0.009, 0. 001), while the intra-group statistical differences of the remaining variances were insignificant (χ2 =0.486, 0. 051, 0. 322, 0. 010, 0. 006, 2. 575, all P > 0. 05). All 9 variances were analyzed by the multi-variance Binary Logistic regression model through for-ward stepwise. The variance of residual thyroid weight (X1) and 131Ⅰ dose (X2) were finally selected as the 2 key parameters in the formula, P=e(-0.865-0.868X1+1.677X2)/1-e(-0.865-0.868X1+1.677X2)] , by the Binary Logistic regression analysis (Wald values were 3.752 and9. 130, P=0.049, 0.003). Conclusions The efficacy of 131Ⅰ ablation of thyroidal remnant in post-operative DTC patients was mainly determined by the re-sidual thyroid weight and the therapeutic 131Ⅰ dose. The other 7 factors included in this study were not found to be statistically significant.