Dynamic Dose Validation Study Of CT-guided Radioactive Iodine 125 Seeds Implantation For Mediastinal Lymph Node Metastases

Objective: The BTPS system was used to validate the feasibility and accuracy of seeds implantation in mediastinal lymph node metastases and to investigate the relationship between the volume of the target area and the dose parameters over time after seeds implantation by simulating changes in the tumour target area.The use of the BTPS system to validate the accuracy of seeds implantation therapy and to simulate the effect of the change in target area over time on the actual dose after particle implantation may better address the uncertainty of the dose change after seeds implantation.Methods: In the first part,the BTPS system was used to simulate the target volume shrinkage over time in 3D space,and groups A～K were divided according to different volume change rates.The BCCA seeds implantation quality standard was used to evaluate the dynamic dose parameters and to initially determine the optimal target volume reduction rate after seeds implantation and the effect on dose.In the second part,the feasibility and accuracy of the technique was firstly verified by comparing the preoperative planning and postoperative dose parameters of 36 cases of mediastinal lymph node metastases implanted with seeds,and further analysing the dynamic dose validation at three months postoperatively to preliminarily analyse the interaction between target area changes and time on dose.The chi-square test and ANOVA statistical methods were applied to compare the clinical efficacy of the groups with different changes in target volume and the doses received by the organs at risk around the target area.RESULTS: 1.BTPS simulated dynamic dose validation of tumour target volumes in different shrinkage speed groups from 1 to 6 months,with a linear relationship between time and dose(D90)for each group.Linear regression analysis of viability and dose assessment parameters showed a statistically significant effect of viability on CI,CI=0.75+(0.305×viability),F = 9.461,p < 0.05.Different shrinkage rate groups were significant for EI and HI.ei was positively correlated with simulated target volume shrinkage rate(B= 251.323,p < 0.005).hi was negatively correlated with simulated target volume shrinkage rate(B =-355.296,p < 0.001)was negatively correlated.A 30%-35% reduction in tumour target volume was optimal,with the seeds dose better encapsulating the target volume over a 6-month period.2.36 patients with mediastinal lymph node metastases were collected and successfully treated with CT-guided implantation of iodine-125 seeds without serious intraoperative injury to vital vessels,organs and vital organs such as the oesophagus.The differences were not statistically significant(p > 0.05)when comparing the postoperative verification with each dose parameter of the preoperative plan.3.Repeated-measures ANOVA of dynamic dose validation parameters at four time points over three months postoperatively in 36 patients suggested an interaction between time and dose in the target volume reduction <30%,30%-35%,and >35% groups of patients with seeds implantation.The interaction between the different target volume reduction rate groups and time had a statistically significant effect on D90 values,F(1,11)= 53.147,p < 0.001.The effect of the time factor on D90 values was statistically significant,F(3,33)= 5.266,p = 0.004.In a twoby-two comparison of measurements at four time points in the 30%-35% group,the effect of the time factor on dose The difference was not statistically significant,p > 0.05.4.Local control rates in the three different groups were 50%,83.3% and 91.7%,respectively,p =0.018,a statistically significant difference.The effective rates in the three different groups were 25%,50% and 83.3% respectively,p = 0.016,a statistically significant difference.5.Using a one-way ANOVA,the difference in mean dose received by the oesophagus between the different target volume groups was statistically significant,F = 21.503,p < 0.001.Conclusion: CT-guided radioactive iodine 125 seeds implantation in mediastinal lymph node metastases did not differ from the preoperative dose indexes,which could better implement the preoperative planning protocol and avoid important organ damage,and was a safe and effective treatment method,which may become a standard procedure with good reproducibility.Post-operative dynamic dose validation of patients can effectively monitor changes in tumour target area and dose,and there is a significant interaction between implantation time and tumour target area reduction on dose.Initially,the dose parameters can be maintained at the desired level when the target volume is reduced in the range of30%-35%.