Analysis Of Influencing Factors For Predicting Individual Thyroid Hormone Withdrawal Time Before Iodine-131 Treatment In Patients With DTC

Objective:Univariate and multivariate analysis were conducted to find out the clinical factors that may affect the time of thyroid hormone withdrawal（THW）before the initial radioiodine treatment（RAIT）in patients with differentiated thyroid cancer（DTC）.These factors can be used to provide the basis for predicting the withdrawal time of patients and individualized withdrawal.Methods:Collect the data of DTC patients who underwent postoperative radioiodine-131(¹³¹I)residual thyroid ablation in Taizhou People’s Hospital from August 2019 to December 2020.The clinical data of patients with complete data were retrospectively analyzed,including gender,age,operation method,gross invasion,pathological type,with or without Hashimoto’s thyroiditis and nodular goiter,TNM stage,recurrence risk stratification,thyroid function index before ablation,thyroid iodine uptake rate,thyroid static imaging and estimated residual thyroid weight,urinary iodine,THW weeks,etc.TSH was measured every week from 2 weeks of THW.When TSH was≥30m U/L,RAIT was arranged.Patients were divided into two groups according to THW 2 weeks and THW more than 2 weeks.（1）Single factor analysis was used to determine the influence of each factor on THW time before the first RAIT.Receiver operating characteristic（ROC）curve was used to analyze the statistically significant measurement data to determine the best cut-off value for predicting THW time.（2）The statistically significant factors in univariate analysis were included in multivariate analysis to determine the independent influencing factors of THW time.（3）Compare the difference of residual thyroid weight between the two surgical methods,and to determine the effect of surgical methods on residual thyroid weight;to analyze the correlation between thyroid iodine uptake rate and residual thyroid weight,so as to determine the feasibility of thyroid iodine uptake rate for evaluating residual thyroid weight.Results:Among 50 patients with DTC who met the inclusion and exclusion criteria,64%（32/50）had TSH of 30 m U/L at 2 weeks and 96%（48/50）had TSH of 30m U/L at3 weeks after THW.32%of the patients were male and 68%were female.The age ranged from 20 to 76 years old,with an average of 49.56±14.222.Total thyroidectomy accounted for 92%,subtotal thyroidectomy only accounted for 8%,intraoperative gross invasion accounted for 32%,and no gross invasion accounted for 68%.The pathological types were all papillary carcinoma.18%of them had Hashimoto’s thyroiditis,82%had no Hashimoto’s thyroiditis,62%had nodular goiter,and 38%had no nodular goiter.Stage T1 36%,T2 8%,T3 30%,T4 26%,N0 16%,N1 84%,M0 94%,M0 6%.The risk of recurrence included 60%moderate-risk and 40%high-risk.The median TSH before THW was 0.61（0.0465～4.64975）m U/L,the median TSH after THW was 44.245（35.45325～61.175）m U/L,the median Tg before THW was 0.3（0.0875～1.335）ng/ml,and the median Tg after THW was 0.3（0.0875～1.335）ng/ml The median thyroid 2-hour iodine uptake rate was 3.85（2.675～5.5）%,the median thyroid 24-hour iodine uptake rate was 2.75（1.3～6.075）%,the median residual thyroid weight was 1.2（0.9～1.925）g,the urinary iodine value of 11 patients was missing,and the median urinary iodine level of the remaining 39 patients was 160（120～191）μg/L.（1）Univariate analysis showed that there were significant differences in TSH level before THW（z=-2.75,P=0.006）,24-hour iodine uptake rate（z=-2.011,P=0.044）and residual thyroid weight（z=-2.671,P=0.008）between the two groups.ROC curve was used to divide the best cut-off value.When TSH level before THW<0.38m U/L,24-hour iodine uptake rate of thyroid≥2.05%,and residual thyroid weight≥1.15g,THW time could be shortened,the area under ROC curve was 0.736（P=0.006）,0.673（P=0.0044）and 0.728（P=0.008）,respectively.According to the best cut-off value,the patients were divided into two groups,namely"≥cut-off value"and"<cut-off value".The difference of THW time between these two groups was statistically significant（P=0.001,P=0.005,P=0.018）.（2）The TSH level before THW,thyroid 24-hour iodine intake rate and residual thyroid weight were included in the multivariate analysis.Binary logistic regression showed that residual thyroid weight was an independent influencing factor of THW time（OR,3.443;95%CI,1.22～9.719,P=0.02）.（3）There was no significant difference in the weight of residual thyroid between total resection and subtotal resection（z=-1.743,P=0.083）;Spearman correlation analysis showed that there was no significant correlation between the weight of residual thyroid and thyroid 2-hour iodine uptake rate（r=0.35,P=0.808）,and there was a significant positive correlation between the weight of residual thyroid and thyroid24-hour iodine uptake rate（r=0.385,P<0.01）,24-hour iodine intake rate can be considered as an alternative of residual thyroid for clinical evaluation.Conclusion:（1）For most patients,2-3 weeks of THW is enough to meet the requirement of TSH≥30mu/L.（2）TSH before drug withdrawal,24-hour iodine intake rate and residual thyroid weight can significantly affect THW time.（3）Only the weight of residual thyroid is the only independent factor.When the weight of residual thyroid is more than 1.15g,the THW time should be extended appropriately.（4）The weight of residual thyroid is less affected by the operation method（total or subtotal resection）;the24-hour iodine uptake rate of thyroid can theoretically partially replace the weight of residual thyroid for clinical evaluation.