Self-absorption correction for (32)p, (198) Au and Re-118 stents: Dose point kernel calculations versus Monte Carlo

Monte Carlo simulations of dose distributions around radioactive stents are very time intensive. Thus, in order to calculate the dose distribution aro und a Re-188 stent, we chose to test a point kernel method, a method which is known to be faster but the accuracy of which has not been established fo r this application. The dose point kernel method, which takes into account absorption in the strut material (=self-absorption). was based on different beta-emitting point source distributions in water by itself and surrounded by steel spheres of different thicknesses. This information was input into an integration routine that modeled either a Palmaz-Schatz or Multilink st ent. The dose distributions around Au-198 and P-32 stents calculated with t he dose point kernel method were compared to those calculated using EGS4 an d MCNP 4B Monte Carlo methods. The resulting correction for self-absorption in steel was distance dependent and averaged 1.12 for P-32 and 1.25 for Au -198 stents. The dose point kernel method gave nearly identical results to these full Monte Carlo simulations and was thus used to calculate the dose distributions around a (188) Re stent. Although Re-188 has a half-life of o nly 17 hours, it is posited to be useful for radioactive restenosis prevent ion, given that a recently developed rapid electrodeposition procedure allo ws stents to be made radioactive, at predetermined activities. within 15 mi nutes. The dose point kernel calculations of a Re-188-coated Multilink sten t were compared to its radiochromic film measurements. The dose fall-off ag reed with the calculations within 5% over 0.4 to 3.5 nim from the stent sur face. The dose point kernel method is a valuable too] to determine depth do se distributions around activated stents taking into account the detailed g eometry and the self-absorption in the struts. It not only requires much le ss processing time than Monte Carlo methods, but also allows the use of hig her resolutions in modeling the geometry, which leads to more accurate self -absorption correction factors. (C) 2001 American Association of Physicists in Medicine.