[Brachytherapy treatment planning calculation (125)I particle esophageal stent dosimetric study]

Objective: To investigate the dosimetric distribution characteristics of (125)I seed stents with different seed spacing, diameter and length, as well as different (125)I seed activity. The dosimetry table of (125)I seed esophageal stent was derived to provide dosimetry for its clinical application. Methods: The self-expanding coated esophagus stent was designed to carry radioactive (125)I seeds with different length, diameter and seed spacing. A cylindrical organic glass model (Thickness 0.8 cm, diameter 20 cm, height 20 cm) was fixed vertically to a cylindrical organic glass containing a solid paraffin (analytical pure) solution. After paraffin cooling and solidification, CT scan was used to transmit image information to TPS. With the center of the bracket as a dot, the cumulative dose at a distance of 1.5, 2.0, 2.5, 3.0, 3.5, 4.0, 5.0, 6.0 and 8.0 cm away from the dot was simulated respectively in 0° and 9° direction. Results: The radial cumulative dose with the seed spacing which was 1.0 and 1.5 cm were different by 4.8%, 5.8%, 7.2%, 8.0%, 8.6% and 13.3% respectively under the exposure of 18.5, 22.2, 25.9, 29.6, 33.3 and 37.0 MBq. When the seed spacing was the same as the length of the stent, the radial cumulative dose with the stent which diameter was 1.3, 2.0, 2.4 cm were different by 4.9% vs 3.4%, 4.7% vs 3.8%, 5.4% vs 6.6%, 4.5% vs 5.3%, 4.7% vs 4.8%, 4.8% vs 5.4% respectively under the exposure of 18.5, 22.2, 25.9, 29.6, 33.3 and 37.0 MBq. When the seed spacing was the same as the diameter of the stent, the radial cumulative dose with the stent which length was 8, 12, 16 cm were different by 1.9% vs 1.2%, 1.7% vs 0.8%, 1.6% vs 1.3%, 1.9% vs 1.5%, 1.7% vs 1.8%, 1.6% vs 1.3% respectively under the exposure of 18.5, 22.2, 25.9, 29.6, 33.3 and 37.0 MBq. Conclusions: The radial cumulative dose of the (125)I seed stent is positively correlated with the activity of the radioactive seeds, Which means the dose rate of a certain point of the (125)I seed stent increase with the increase of the activity of the radioactive seeds. The stent of the (125)I radioactive seeds is negatively correlated with the distance, the dose rate of the (125)I seed stents decrease rapidly with the increase of distance.