Dosimetry comparison of esophageal stents carrying different diameters of radioactive 125I seeds / 介入放射学杂志

ABSTRACT

Objective To investigate the dose distribution of esophageal stents carrying different diameters of radioactive 125I seeds in tumor target area. Methods A laser scanner was used to scan a piece of blank paper on which circles of 12 mm, 14 mm and 16 mm diameter and a 5 cm scale were drawn. The data were stored in JPEF format on the computer desktop. According to the circular diameter, simulations of the corresponding esophageal stents were established, which were divided into group A, group B and group C. By using image conversion program, 17 images with 5 mm slice-distance were created for each group; the images were transmitted to the computer treatment planning system (TPS) to simulate the 8 cm long esophageal stents of different diameters. TPS was used to sketch the gross tumor volume (GTV) in order to simulate the esophageal stent border that was used as the inner boundary of GTV, which was expanded 0.5 cm outward to be used as the external boundary of GTV. Beginning from the fifth level, the 4 cm-long GTV was drawn with circles. Setting the same prescription dose, from the fifth level to the thirteenth level the 125I seeds with 0.3, 0.4, 0.5, 0.6, 0.7, 0.8 and 0.9 mCi were successively loaded on the simulation of the esophageal stents. The distance between 125I seed layers was 1 cm; the average number of seeds distributed on each layer was 4 particles. The dose volume histogram (DVH) was obtained. The D90 (the dose received by 90% of the target) and V90 (the percentage of the GTV volume receiving 90% the prescription dose) were recorded.Result s The arithmetic mean D90 of group A, B and C was (77.24 ±19.92) Gy, (69.56 ±25.27) Gy and (56.38±20.08) Gy respectively, and no statistically significant differences existed between each other among the three groups (F=0.84,P=0.44). The V90 of group A, B and C was (77.76±30.73)%,(76.79±25.92)%and (64.10 ±32.49)% respectively, and no statistically significant differences existed between each other among the three groups (F=0.46,P=0.64). Conclusion When the diameter of radioactive esophageal stent is 12 mm, the activity of 125I seed of 0.6 mCi is recommended. When the diameter of radioactive esophageal stent is 14 mm or 16 mm, the activity of 125I seed of 0.7 mCi is recommended. Nevertheless, when the diameter of radioactive esophageal stent is 16 mm, distribution of every five 125I seeds on each layer is strongly recommended. These three kinds of esophageal stent diameter have no significant effect on the dosimetric parameters.