Dose effects of stents in intravascular brachytherapy for in-stent restenosis: a Monte Carlo calculation

Abstract

Purpose: Intravascular brachytherapy (IVBT) has been recognized as a preferred treatment for coronary in-stent restenosis (ISR) in routine practice. Stents made of high-Z materials will inevitably perturb the dose distribution of IVBT. In this work, we have conducted a systematic study on these dose perturbations for three commercially available IVBT sources. Methods and Materials: The EGSnrc Monte Carlo codes were used to calculate the dose distributions for the 90Sr, 32P, and 192Ir IVBT sources with and without a metallic stent in place. The ring stent type made of different material and with different strut size, metallic surface area (MSA), and radius was studied. Results: Calculations show that dose enhancement of 5% to 20% occurs inside stent in the region close to the stent struts (luminal side) for all three sources. In the region outside stent (adventitial side), dose reduction of 5% to 20% is observed for a beta source, whereas the dose effect is negligible for the gamma source. For a given stent design, the tantalum stent yields a larger dose effect than other stents made of steel, Ti, Ni, or nitinol. It is found that the dose effect significantly depends on strut thickness, and it is strongly correlated to MSA. The MSA may be used to characterize the dose effect of a stent. Sample empiric equations to relate the dose perturbations to MSA for a given source, a stent material, and a strut thickness were derived. Conclusions: The dose perturbations due to the presence of metallic stents were found to be significant in IVBT for ISR. The dose effects of a stent can be estimated from its MSA based on derived empiric equations. The data presented are practically useful to consider the dose effects of stents in dose evaluation/treatment planning for using IVBT to treat ISR.