| Objectives:Radioiodine 131 therapy is an essential step in the treatment of differentiated thyroid carcinoma.When patients with differentiated thyroid carcinoma are treated with radioactive iodine 131,the external body dose rate is an important basis for assessing whether the residual activity of radioactive iodine in the patient’s body is within the radiation safety range.However,the factors that influence the rate of decay of the external body dose rate in patients are unclear.Therefore,this study aimed to use clinical data from patients with differentiated thyroid carcinoma before and after iodine administration to explore the pattern of changes in external body dose rate over time and the factors influencing them,as well as to determine the current status of external body dose rate attainment and the influencing factors at different times after iodine administration.The aim is to assist clinicians in assessing the residual activity of radioactive iodine in the patient’s body,predicting the time of discharge,and reducing the harm to the surrounding population from radiation exposure.Methods:The study was based on 1336 patients with differentiated thyroid cancer who had completed total or near-total excision of thyroid tissue and were treated with radioactive iodine 131 for the first time.The research data were obtained from the patient’s clinical data in the hospital’s electronic medical record system and the external body dose rate test results of the patients after iodine administration in the consultation records.An exponential function of the external body dose rate decayed at any time after the patients took iodine was determined by plotting to scatter plots,and an exponential speed index reflecting the overall decay rate of the patient’s external body dose rate was extracted.The effect of each study variable on the exponential speed index was analyzed using single-factor linear regression and multifactor linear regression.Patients were then divided into two groups according to whether the external body dose rate was achieved24 hours,48 hours,and 72 hours after iodine administration,using the cut-off point of≤25μSv/h as specified in the Radiation Protection Requirements for Nuclear Medicine.The factors affecting the reduction of the patient’s external body dose rate to the radiation safety range were determined using univariate logistic regression and multifactor logistic regression models.Results:1.A total of 1336 patients with differentiated thyroid carcinoma were included in this study.88.3%of the patients’age were under 55 years.There was a significant gender difference among the patients,with female patients accounting for 72.4%of the total number of patients.The majority of the patients’pathological type was papillary thyroid cancer（99.5%）.2.When differentiated thyroid carcinoma patients are treated with radioactive iodine 131,the external body dose rate decays exponentially over time.The greater the exponential speed index of the patient,the slower the rate of decay of the patient’s external body dose rate.In this study,19（1.42%）differentiated thyroid cancer patients achieved the radiation dose safety range within 24 hours after iodine administration,633（47.38%）patients achieved the radiation dose safety range within 24 to 48 hours after iodine administration and 1295（96.93%）patients achieved the radiation dose safety range within 48 to 72 hours after iodine administration.3.The results of the multiple linear regression of the study variables on the exponential speed index showed that the higher the body mass index,the history of type2 diabetes,the type of pathology of follicular thyroid cancer,the larger the residual thyroid tissue,and the higher FT3 or FT4,the greater exponential speed index in differentiated thyroid cancer patients（P<0.05）,while the lower the 131I dose and the N0（no lymph node metastasis）in men,the greater the exponential speed index in differentiated thyroid cancer patients（P<0.05）.Logistic regression of the study variables and the achievement of the external body dose rate within 24 hours of iodine administration showed that 131I dose was a risk factor for achieving the safe range within24 hours of iodine administration in differentiated thyroid cancer patients（OR=0.944,95%CI=0.925-0.963）.Logistic regression analysis of the study variables in relation to patients achieved the external dose equivalent rate 24 to 48 hours after iodine administration showed that men（OR=2.605,95%CI:1.934-3.510）,with a history of type 2 diabetes（OR=0.472,95%CI:0.252-0.883）,higher 131I treatment dose（OR=0.958,95%CI:0.952-0.965）,high TSH（OR=0.997,95%CI:0.995-0.999）and higher FT4（OR=0.796,95%CI:0.712-0.891）were risk factors affecting patients’external body dose rate to safe requirements within 24 to 48 hours after iodine administration.Logistic regression analysis of the study variables in relation to patients achieved the external dose equivalent rate 48 to 72 hours after iodine administration showed that a history of type 2 diabetes（OR=0.274,95%CI:0.094-0.800）,higher TSH（OR=0.994,95%CI:0.990-0.999）,higher FT4（OR=0.603,95%CI=0.519-0.702）and follicular thyroid cancer（OR=0.081,95%CI:0.013-0.515）were risk factors for patients to achieve external dose equivalent rates within 48 to 72 hours after iodine administration.Conclusion:1.External body dose rate in differentiated thyroid cancer patients with iodine showed exponential decay over time.Sex,iodine dose,N stage,body mass index,history of type 2 diabetes,residual thyroid tissue size,pathology type,FT3,and FT4were factors that influenced the exponential speed index of external body dose rate during 131I treatment in differentiated thyroid cancer patients.2.The majority of differentiated thyroid cancer patients achieved an external body dose rate within the radiation safety range within 72 hours of iodine administration,although 3.0%of patients failed to achieve this range.131I treatment dose was the main factor influencing the external body dose rate reaching the safe range within 24 hours of iodine administration in patients with differentiated thyroid cancer.Sex,history of type 2 diabetes,131I treatment dose,TSH,and FT4 were factors influencing the external body dose rate to reach the safe range 24 to 48 hours after iodine administration.History of type 2 diabetes,type of pathology,TSH,and FT4 were factors influencing the external body dose rate to reach the safe range 48 to 72 hours after iodine administration. |
