The Impact Of Nickel-titanium Alloy Stent On Radiotherapy Dose Distribution

Objective:The purpose of the study is to investigate the change of dose distribution accepted by the esophageal carcinoma patients with nickel-titanium alloy esophageal stent during a radiotherapy procedure, and to give some reasonable suggestion to make radiotherapy plans.Methods:A nickel-titanium alloy stent was imbedded in the position of esophageal in an anthropomorphic phantom material mimicking, the thermoluminiscent chips (TLD)were set on the surface of stent. At first the target was irradiated with a 15MV-X ray beam and the field was 7 cm×15 cm, the source-skin distance was 100 cm. A contrastive analysis was done to explain the effects for the stent. And then an isocenter irradiation was given with three beams of which incident angles were 0°,135°,230°, sizes were 7 cm×15 cm,5 cm×15 cm,5 cm×15 cm respectively, with the body model,stent and thermoluminiscent chips in the same position, a contrastive analysis was also done. And the results were compared to the calculations by the therapy plan system(TPS).Result:The measurements of the single external beam showed an increase in absorbed dose of up to 9.02% at the anterior surface of the middle of stent(A), While the dose difference was not significant at the other surface of the stent (B,C,D,E,F). Dose change within a range of 2 cm from the surface of stent was not seen in TPS. The increase in absorbed dose of 15.60% and 18.01% were observed respectively at the anterior surface and the posterior surface of the middle of stent (A,C)while using three external beams, there was no dose change within a range of 2 cm from the surface of stent in TPS.Conclusion:For a single external beam, the presence of stent increased the dose of the anterior surface of the middle of stent and of the region of the edge of stent, three external beams made the difference more obvious. If the position of tumor is decentered , it could lead to radiation damage, so the esophageal carcinoma patients with nickel-titanium alloy esophageal stent should not be irradiated with three isocenter external beams. The radiation dose should be amended according to patient conditions,the type of stent and the position of tumor while making radiotherapy plans.