Monte Carlo calculations of dose distributions around P-32 and (198)AU stents for intravascular brachytherapy

3D dose distributions are calculated for a P-32 impregnated stent and a Au- 198 Stent fur intravascular brachytherapy with the EGS4 Monte Carlo simulat ion code. The stents were modeled as a combination of eight helicoidal stru ts. This allowed investigation of the effect of the stent geometry and the electron absorption in the strut material on the dose distributions. Absorb ed dose to water was calculated at radial distances ranging from 50 mu m to 5 mm from the stent surface. The dose distributions around the stents are compared to the dose distribution around an intravascular brachytherapy Ir- 192 source, also calculated with the EGS4 Monte Carlo code. The dose profil es near the struts show hot spots. At 50 mu m distance a peak to valley rat io of 3 for P-32 and 6 for Au-198 in the dose distribution is obtained. For both the isotopes the inhomogeneities decrease with distance and at a radi al depth of 350 mu m the effect becomes negligible. The calculations showed the importance of the effect of the absorption in the stent material as th is leads to a dose decrease to 67% for the Au-198 Stent and to 77% for P-32 near the stent at a distance of 2 mm from the stent axis. It is concluded that from the dosimetric point of view, the Au-198 Stent is inferior to the P-32 stent and the Ir-192 source. Application of the Au-198 Stent in clini cal practice requires further investigation of the importance of the advent itia in the restenosis process, and the tolerance dose of the intima. (C) 1 999 American Association of Physicists in Medicine. [S0094-2405(99)02108-2] .