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 thyroidectomy 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 successful only if no conceivable radioactivity was detected in the thyroidectomy bed. The χ2 test and multi-variance 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 and 9. 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 residual thyroid weight and the therapeutic 131I dose. The other 7 factors included in this study were not found to be statistically significant. (authors)