RESUMO
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.
RESUMO
Objective To study the dose distribution in tumor target of radioactive esophageal stent covered with 125I seeds which are arranged at different distance. Methods According to the longitudinal and horizontal distance between the 125I seeds, the experiment was divided into group A (0.5 cm), group B (1.0 cm) and group C (1.5 cm). A sheet of white paper, on which a 2cm diameter circle was drawn and was marked with a 5 cm scale, was scanned with a laser scanner, and the scanning data were saved in JPEG format on the computer desktop. By using image conversion program, pictures of 17 layers with the layer space of 5 mm were created. The picture was transmitted to the computer treatment planning system (TPS) to simulate a 2 cm diameter and 8 cm length esophageal stent. Using TPS to delineate the tumor target area (gross tumor volume, GTV), which was used as the simulation of the inner boundary of the tumor target area, outward expansion of 0.5 cm being regarded as the outside border. An annular and 6cm length tube was delineated and it was used as the target area, and the same prescription dose was set, and in each group 125I seeds of 0.3, 0.4, 0.5, 0.6, 0.7, 0.8 and 0.9 mCi were successively loaded on the simulation of esophageal stent. With the help of TPS the DVH graph was obtained, and the D90 (the dose received by 90% of the target) and V90 (the percentage of the GTV receiving 90% the prescription dose) of the three groups were determined. The results were statistically analyzed. Results The arithmetic mean values of D90 of group A, B and C were (217.15± 19.92), (89.16±32.44) and (31.68±11.52) Gy respectively (F=159.18, P<0.05); and the arithmetic mean values of V90 of group A, B and C were (100.00±0.00)%, (86.47±21.36)%and (29.33±21.54)%respectively (F=32.11, P<0.05). Conclusion The 2 cm-diameter radioactive esophageal stent covered with 125I seeds, which have o.6mci activity and are arranged at 1.0cm distance in both longitudinal and horizontal directions, should be recommended in clinical practice.
