To investigate the influential factors for the outcome of the first ¹³¹I therapy in patients with PTC after total thyroidectomy.

One hundred and fifty-nine patients (45 males, 114 females, average age (43.4±12.2) years) with PTC after total thyroidectomy who underwent ¹³¹I therapy from July 2014 to December 2015 were retrospectively analyzed. Curative efficacy was evaluated 6 months after ¹³¹I therapy. Therapeutic outcome was evaluated according to TSH stimulated Tg (sTg) level, Dx-WBS and evidences of other imaging modalities. Twelve possible factors affecting therapeutic outcome of ¹³¹I therapy, including patients′ age, gender, time interval between thyroidectomy and ¹³¹I therapy, primary tumors size and extrathyroidal extension, number and range of primary tumor lesions, lymph node metastases in surgery, status of thyroid remnant in ⁹⁹Tc^mO₄^- imaging, pre-treatment laboratory measurements (TSH, sTg and TgAb), ¹³¹I therapeutic dose, results of Rx-WBS and SPECT after ¹³¹I therapy, were analyzed with univariate and multivariate logistic regression. ROC curve and diagnostic critical point were analyzed to evaluate the predictive value of influential factors for the outcome of ¹³¹I therapy.

The cure rate of the first ¹³¹I therapy was 64.2%(102/159). Univariate logistic regression analysis showed that age, gender, lymph node metastases, sTg and ¹³¹I therapeutic dose (all P<0.01) were the influential factors for the outcome of ¹³¹I therapy. Multivariate logistic regression analysis showed that lymph node metastases (regression coefficient: 1.118) and sTg (regression coefficient: 0.314) were influential factors (both P<0.05). The regression equation was: Logit P=-4.155+ 1.118×lymph node metastases+ 0.314×sTg (χ²=93.7, P<0.001). Taking sTg as a predictive factor for the outcome of ¹³¹I therapy, the AUC of ROC curve was 0.926 (95% CI: 0.888-0.963). The cut-off value of sTg was 2.97 μg/L with a sensitivity of 94.7%(54/57) and a specificity of 76.5%(78/102).

PTC patients with low sTg levels and few lymph node metastases after total thyroidectomy are more likely to be cured in the first ¹³¹I therapy.

Thyroid neoplasms; Radiotherapy; Iodine radioisotopes; Treatment outcome