真实胆管弧度下胆道支架联合125I粒子条治疗恶性梗阻性黄疸的剂量学研究

Biliary stent combined with 125I seed strand implantation under real biliary radian guidance in the treatment of malignant obstructive jaundice: a dosimetric study

目的 比较胆道支架联合I粒子条在胆管弧度下和直线排列下的剂量学差异,评估粒子条在胆管弧度下危及器官(organ at risk, OAR)的受量情况,为胆道支架联合粒子条治疗恶性梗阻性黄疸疾病(malignant obstructive jaundice,MOJ)的有效性及安全性提供剂量学参考。方法 收集行术后验证的18例患者的CT图像导入治疗计划系统(treatment planning system,TPS),靶区及OAR进行勾画,同时制作出治疗计划,并定义为真实胆管组。直线模型组为按照每例患者植入支架的尺寸、粒子条的粒子数及梗阻段的长度在TPS上制作出直线模型并制作计划。统计分析两组靶区在剂量体积参数、适形指数(conformity index,CI)、靶区外体积指数(external index,EI)及均匀指数(homogeneity index,HI)上的差异,并且评估粒子条处于真实胆管弧度状态时,OAR在各粒子活度下的受量情况。结果 与直线模型组相比,真实胆管弧度会降低两靶区的D、D、D,且下降幅度与粒子活度成正比,也会降低两靶区的V、V、V、V。其中,当使用粒子活度为0.8 mCi的粒子条时,真实胆管组靶区一的D、V、V分别为70.98 Gy、93.81%、43.48%;当使用粒子活度为1.0 mCi的粒子条时,真实胆管组靶区二的D、V、V分别为59.95 Gy、84.45%、31.88%。两靶区的CI、EI、HI均较差,与直线模型组相比,真实胆管弧度会降低CI,而在一定程度上改善EI及HI。串行器官中除肝动脉及肝门静脉的照射受量较高,最大剂量(maximum dose,D)分别为105.28~210.56 Gy、257.53~515.05 Gy,其他组织照射受量均较低。并行器官中胃的D为80.25~160.50 Gy,十二指肠的V30 Gy、V50 Gy分别为5.29~13.81 cm^(3)、2.11~7.09 cm^(3),胰腺的D为9.00~17.99 Gy,肝肾的照射受量较低。结论 与直线模型相比,胆管弧度会降低肿瘤靶区的剂量体积参数及适形度,但能改善靶区的均匀度及靶区外的受照体积。对于胆管壁无明显增厚的MOJ,植入粒子活度为0.8 mCi的粒子条,胆管EQD2可达到60 Gy。

Objective To compare the dosimetric differences of biliary stent combined withI seed strand implantation between real biliary radian guidance and linear arrangement guidance, and to evaluate the radiation dose of organ at risk(OAR) when the seed strand is in real biliary radian, so as to provide a dosimetric reference for the assessment of efficacy and safety of biliary stent combined with seed strand implantation in treating malignant obstructive jaundice(MOJ). Methods The computed tomography(CT) images of 18 patients who underwent postoperative validation were imported into treatment planning system(TPS), and then the target area and OAR were outlined. At the same time, the treatment plan was formulated, which was employed in patients of real bile duct group. According to the size of stent, the number of seeds and the length of obstructed segment, the linear model was made on the TPS, the treatment plan was formulated, which was employed in patients of linear model group. The dose volume parameters, conformity index(CI), external index(EI) and homogeneity index(HI) of the target area were compared between the two groups, and the dose of OAR at each seed activity was evaluated when the seed strand was in real biliary radian state. Results Compared with the linear model group, the real biliary radian could decrease D, Dand Dof the two target areas, and the decline magnitude was proportional to the particle activity, and the V, V, Vand Vof the two target areas were also decreased. In real bile duct group, the D, Vand Vof target area Ⅰ were 70.98 Gy, 93.81% and 43.48% respectively when the seed activity was 0.8mCi;the D, Vand Vof target area Ⅱ in real bile duct group were 59.95 Gy, 84.45% and 31.88% respectively when the particle activity was 1.0mCi. The CI, EI and HI of the two target areas were poor. Compared with the linear model group, the real biliary radian could decrease CI while improve EI and HI to a certain extent. Among the serial organs,the radiation dose of the hepatic artery and the hepatic portal vein was much high, the maximum dose(D) of hepatic artery and hepatic portal vein were 105.28-210.56 Gy and 257.53-515.05 Gy respectively, and radiation dose of other organs was low. Among the parallel organs, the Dof stomach was 80.25-160.50 Gy,the Vand Vof duodenum were 5.29-13.81 cm^(3) and 2.11-7.09 cm^(3) respectively, and the Dof pancreas was 9.00-17.99 Gy. The radiation dose of the liver and kidney was low. Conclusions Compared with the linear model group, biliary radian can reduce the dose volume parameters and conformal degree of the tumor target areas, but it can improve the uniformity of the target area and the irradiation volume outside the target area. For the treatment of MOJ with no obvious thickening of bile duct wall, the use of seed strand with the activity of 0.8 mCi can enable the equivalent dose(EQD2) of bile duct to reach 60 Gy level.