The Relationship Between The Different Level Of Preablative TSH And Its Response To ¹³¹I Therapy In Patients With Low To Intermediate Risk Differentiated Thyroid Cancer

Objective:The objective of this study was to investigate the relationship between the different level of preablative TSH after thyroid hormone withdrawl and its response to ¹³¹I therapy in patients with low to intermediate risk DTC after total or subtotal thyroidectomy,and to explore the potential factors that may impact their responses.Methods:A total of 186 low to intermediate risk DTC patients[59 males,127 females,age14-68years,average age（44.97±12.58）years]were retrospectively reviewed in our hospital.The surgical treatment way of all patients is total or near-total thyroidectomy.The pathologic type of all patients are papillary thyroid carcinoma.Serum TSH and thyroglobulin（Tg）levels were measured right before ¹³¹I treatment after thyroxine hormone withdrawal（THW）.Patients were categorized by their preablative TSH level grouping A-F of less than 30（n=9）,30 to less than 60（n=22）,60 to less than 90（n=34）,90 to less than 120（n=43）,120 to less than 150（n=30）,and 150 mU/L or greater（n=48）.All patients have 2 times of ¹³¹I therapy,the first ¹³¹I treatment dose was3700MBq,the second ¹³¹I treatment dose was 3700-5550MBq,followed up for 6-12months,the follow-up contents included serum TSH level and Tg level,cervical ultrasound,chest CT and other examination results.Responses to ¹³¹I therapy were evaluated as excellent,indeterminate,biochemical incomplete,or structural incomplete response（ER,IDR,BIR,or SIR）according to 2015 American ATA guidelines.The treatment efficacy,general clinicopathological features,residual thyroid volume and preablative Tg（ps-tg）were analyzed and compared in different TSH levels group.That is likely to affect the treatment effect of other factors(including age,sex,T stage,N stage,operation method,residual thyroid volume,the time from operation to the first ¹³¹ I treatment and ps-Tg level)on the single factor analysis of the influence on curative effect.The results of single factor analysis showed that there were statistically significant influencing factors and multivariate Logistic regression analysis was performed to analyze its effect on therapeutic effect.Results:1.91 of 186 patients（48.9%,91/186）had achieved ER,45 patients were IDR（24.2%,45/186）,32 patients were BIR（17.2%,32/186）,18 patients were SIR（9.7%,18/186）.136 patients were ER+IDR（73.1%,136/186）,50 patients were BIR+SIR（26.8%,50/186）.2.ER+IDR was observed in 55.5%,68.2%,70.6%,79.1%,73.3%and 75%respectively at A-F groups,BIR+SIR was observed in 44.5%,31.8%,29.4%,20.9%,26.7%and 25.0%respectively.Group 90 to less than 120 mU/L presented the highest rate of ER+IDR and lowest rate of IR,there were statistically significant when compared with other groups（χ²=10.897,P=0.043）.3.Univariate analysis revealed that the sex（χ²=4.761,P=0.029）,the volume of thyroid residue（χ²=9.376,P=0.002）,the preablative level of TSH（U=2614,P=0.015）,and the preablative level of Tg（U=5552,P<0.001）were the important influence factors of response to ¹³¹I therapy.Multivariate logistic regression showed that the preablative level of TSH（Wald=4.508,P=0.034）and preablative Tg（Wald=15.530,P<0.001）as influence factors of response to ¹³¹I therapy.Conclusion:1.The therapeutic effect of ¹³¹I was closely related to the TSH level before ¹³¹I treatment.A preablative TSH level of 90 to less than 120 mU/L might be more appropriate for patients with low to intermediate risk DTC to achieve better response to¹³¹I therapy.2.Postoperative residual thyroid tissue,TSH level,Tg level and gender affected the therapeutic effect of patients with low to intermediate risk DTC,of which ¹³¹ I therapy before TSH level and ps-Tg level are the important factors influencing the effect of ¹³¹ I treatment.