| OBJECTVE: As a very important part of the best therapy scheme for differentiated thyroid cancer(DTC), post-surgical radioiodine therapy includes two steps. One is radioiodine ablation of thyroid remnants, the other is radioiodine therapy for metastases of DTC. Ablation of functioning residual thyroid tissue by radioiodine can reduce the long-term risk of recurrence and death of thyroid cancer. It can increase the sensitivity and specificity of serum thyroglobulin(Tg) measurements and diagnostic 131I scanning for the detection of persistent or recurrent disease. It can benefit to thyroid cancer following-up. First ablation of thyroid remnants will be directly affect the scheme for the patients. If first ablation not achieved, it would be more hard for the second ablation. The primary aim of this study was to observe the effect factors of first radioiodine ablation of post-operation thyroid remnants in patients with differentiated thyroid carcinoma.METHODS: For 38 no metastasis of differentiated thyroid cancer patients after surgery , a empirically determined 'fixed'high ablative dose of 131I (80mCi~100mCi) was given. Compared with the low ablative dose of 131I (50mCi~70mCi) group that including 56 patients who accepted radioiodine ablation before. 38 patients was divided into two groups by the ablative results. Group 1 was ablation achieved, group 2 was ablation failed. Observed the difference of age, sex, histological type, operation methods, time from operation to radioiodine ablation, serum TSH levels between group 1 and group 2. operation methods were evaluated by uptake and thyroid remnants volumes measured by ultrasound. Measurement serum Tg before radioiodine treatment administration(Tg1) and 5 days after treatment administration(Tg2). Observe the predicting value of serum Tg changing in first radioiodine ablation. Statistical calculation were performed by using SPSS for windows, Version 11.5.RESULTS: We observed complete ablation 25 of 38 (65.8%) in high dose group. Ablation rate was significantly higher than low dose group(P<0.05). There was no significantly difference in age, sex, histological type between the two groups. Time from operation to radioiodine ablation in group 1 was shorter than group 2, but there was no significant difference(P=0.192>0.05). There was significant difference in operation type and serum TSH levels between the two groups . 24h 131I uptake and residual thyroid volumes in group 1 were significantly lower than group 2 (P<0.05). 24h 131I uptake was correlation with residual thyroid volumes(r=0.691, P=0.001<0.05). Serum TSH levels was significantly in group 1 higher than group 2 (P=0.004<0.05). serum Tg before radioiodine treatment administration(Tg1) was no significant difference between the two groups, but serum Tg 5 days after treatment administration(Tg2) in group 1 was significantly higher than group 2 (P=0.001<0.05), serum Tg changing in group 1 was also higher than group 2 (P=0.019<0.05).CONCLUSIONS: High ablative dose of 131I is better than low dose in first radioiodine ablation post-surgical thyroid remnants. Operation type is more complete, residual thyroid tissue is more less, the result of radioiodine ablation is more better. Serum Tg levels 5 days after treatment administration is more higher, the opportunity of ablation achieved is more larger. Serum Tg levels changing 5 days after treatment administration could be a good predictor of first radioiodine ablation of post-surgical thyroid remnants treatment efficacy.
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