组织成分及密度对125I粒子植入剂量分布影响的研究

目的 分析组织成分及密度对¹²⁵I粒子植入剂量分布影响，为临床放射性粒子植入剂量计算和评估提供参考。方法 应用egs_brachy软件建立OncoSeed 6711型¹²⁵I放射性粒子物理模型，计算剂量率常数和水中径向剂量函数g（r），以验证计算模型准确性；根据不同组织的元素组成及密度表，分别计算¹²⁵I粒子在水、前列腺、乳腺、肌肉、骨等不同介质中g（r）和剂量分布。结果 计算得到的剂量率常数为0.950 cGy·h^-1·U^-1、水中g（r）和吸收剂量均与文献数据近似。在同一径向位置，¹²⁵I粒子在前列腺、肌肉中吸收剂量与水中差异<5%；在距源中心0.05 cm处，骨中吸收剂量是水中的6.042倍；在近源1.7 cm内，乳腺与水中吸收剂量差异均>10%。结论 ¹²⁵I粒子在部分介质中的剂量分布与水有着较明显区别，在临床剂量计算中需考虑组织成分及密度对吸收剂量的影响。

Impacts of the composition and density of tissue on the dose distribution of implanted 125I seeds

Objective To investigate the impacts of the composition and physical density of tissue on the dose distribution of implanted ¹²⁵I seeds, in order to provide references for the clinical dose calculation and assessment of implanted radioactive particles. Methods The OncoSeed 6711 physical model of ¹²⁵I seeds was established using thes of twareegs_brachy and was validated through the calculation of dose rate constant and the radial dose function[g(r)] in water. Then, based on the element composition and physical density of different types of tissue, the g(r) and absorbed dose ratein water, prostate, breast, muscle, and bone were calculated. Results The calculated dose rate constant (0.950 cGy·h^-1·U^-1) and g(r)in water approached the values in related literature. The absorbed dose in bone was 6.042 times than that in water at a distance of 0.05 cm from the implanted source. The difference between the absorbed doses in breast and water was more than 10% at a distance of less than 1.7 cm from the implanted source. The difference between the absorbed doses in prostate/muscle and water was less than 5% at the same radial location. Conclusions The dose distribution of ¹²⁵I seeds in some types of human tissue is significantly different from that in water, which should be carefully considered in clinical dose calculation.