The Prediction Value Of Tavc/Lavc On I-131 Whole Body Scan For Thyroid Remnant Ablation With Low Doses ¹³¹I-iodine In Low Or Intermediate Risk Differentiated Thyroid Carcinoma

Objective:The aim of the paper was to observe the roles of the average pixels of residual thyroid tissue（Tavp）,radioactivity counts ratio of residual thyroid tissue per pixel to liver（Tavc/Lavc）and residual thyroid tissue per pixel to thigh（Tavc/Thavc）on posttreatment ¹³¹I-iodine whole body scan（Rx-WBS）in evaluating the effect of thyroid remnant ablation with low doses ¹³¹I-iodine in low or intermediate risk differentiated thyroid carcinoma（DTC）.Methods:Twenty patients with low or intermediate risk DTC who received total or near total thyroidectomy were enrolled in this study and the mean age was 45.37±10.69years（1M,19F,age range:26-68 years）.There were a total of 31 thyroid remnants in 20patients.All patients received the initial ¹³¹I-iodine dose 1110-1850 MBq（30⁵0 mCi）,The mean dose was 1616.32±353.40MBq（43.68±9.55mCi）.Serum TSH,Tg and TgAb were measured and ^99mTcO₄^-thyroid scan was performed before thyroid remnant ablation with ¹³¹I-iodine.The Rx-WBS were performed on the 7th day after the ablation treatment.The average count per pixel from the standard region of interest analysis of the thyroid bed（Tavc）,liver（Lavc）and thigh（Thavc）were obtained.At the 6th month after the treatment,Rx-WBS were performed to 20 patients to evaluate the success of ablation treatment.According to the second Rx-WBS,thyroid remnant ablation with¹³¹I-iodine were divided into three groups:（1）Completion of ablation:the second Rx-WBS show that the residual thyroid tissue completely disappear;（2）Most part ablation:thesecond Rx-WBS show that the residual thyroid tissue were mostly ablation:the average radioactive count per pixel of remaining residual thyroid tissue is higher than in the background（soft tissue of thighs outside）and lower than in the liver;（3）partly ablation:the second Rx-WBS show that the residual thyroid tissue a little cleared:the average radioactive count per pixel of remaining residual thyroid tissue is higher than in the liver.The above two groups mentioned later are collectively called part radioactive iodine therapy.Results:1.31 thyroid residual tissues in 20 patients after the first thyroid remnant ablation with low dose ¹³¹I-iodine,21thyroid remnants were completely cleared;10 thyroid remnants were partly removal,of which 4 were mostly cleared and 6 were partly cleared.The success rate is 67.7%in complete ablation（21/31）;the effective cleared rate（mostly cleared and partly cleaed）is 80.6%（25/31）.2.In the first Rx-WBS,Tavc/Lavc value in group（1）（51.57±54.01）and group（2）（179.66±154.49）,group（1）and group（3）（155.45±151.81）had statistical differences（Z=-2.246,P=0.025;Z=-2.268,P=0.023）;Tavc/Thavc value in group（1）（140.51±145.08）and group（2）（1006.34±1225.23）,group（1）and group（3）（998.88±1428.15）had statistical differences（Z=-2.298,P=0.022;Z=-2.325,P=0.020）.3.In the first Rx-WBS,Tavp value in group（1）（139.24±49.72）and group（3）（216.33±58.71）,group（2）（127.00±52.25）and group（3）had statistical differences（Z=-2.581,P=0.010;Z=-2.174,P=0.030）;group（1）and group（2）had no statistical differences（Z=-0.382,P=0.703）.4.The serum s-TSH value before thyroid remnant ablation in group（1）（84.40±26.86）and group（3）（56.01±41.34）had statistical differences（Z=-2.390,P=0.017）;group（1）and group（2）（75.09±28.51）,group（2）and group（3）（56.01±41.34）had no statistical differences（Z=-1.058,P=0.290;Z=-0.820,P=0.412）.Conclusion:1.After the first thyroid remnant ablation with low dose ¹³¹I-iodine,the completion of ablation rate is 67.7%（21/31）and the effective of ablation cleared rate is 80.6%（25/31）.2.Tavc/Lavc and Tavc/Thavc value in the first Rx-WBS both were the important index to evaluate the effect of thyroid remnant ablation with low doses ¹³¹I-iodine.3.Tavp value in the first Rx-WBS and the serum s-TSH value before thyroid remnant ablation can be as auxiliary predicting index to evaluate the effect of thyroid remnant ablation with low doses ¹³¹I-iodine.