title: Dose perturbation of a novel cobalt chromium coronary stent on 32P intravascular brachytherapy: a monte carlo study.
abstract: Intravascular brachytherapy has been adopted for the indication of in-stent restenosis on the basis of results of clinical trials using mainly stainless steel stents. Recently, a new stent made of cobalt-chromium L-605 alloy (CoCr, p=9.22 g/cm3) (MULTI-LINK VISION) was introduced as an alternative to the 316L stainless steel stent design (SS, p=7.87 g/cm3) (MULTI-LINK PENTA). In this work, we used the Monte Carlo code MCNPX to compare the dose distribution for the 32P GALILEO source in CoCr and SS 8 mm stent models. The dose perturbation factor (DPF), defined as the ratio of the dose in water with the presence of a stent to the dose without a stent, was used to compare results. Both stent designs were virtually expanded to diameters of 2.0, 3.0, and 4.0 mm using finite element models. The complicated strut shapes of both the CoCr and SS stents were simplified using circular rings with an effective width to yield a metal-to-tissue ratio identical to that of the actual stents. The mean DPF at a 1 mm tissue depth, over the entire stented length of 8 mm, was 0.935 for the CoCr stent and 0.911 for the SS stent. The mean DPF at the intima (0.05 mm radial distance from the strut outer surface), over the entire stented length of 8 mm, was 0.950 for CoCr, and 0.926 for SS. The maximum DPFs directly behind the CoCr and SS struts were 0.689 and 0.644, respectively. All DPF estimates have a standard deviation of +/-0.6%(k=2), approximating the 95% confidence interval. Although the CoCr stent has a higher effective atomic number and greater density than the SS stent, the DPFs for the two stents are similar, probably because the metal-to-tissue ratio and strut thickness of the CoCr stent are lower than those of the SS stent.
authors.affiliation: Department of Radiation Physics, The University of Texas M D Anderson Cancer Center, Houston, Texas 77030, USA. fmourtad@mdanderson.org
authors.forename: Firas
authors.initials: F
authors.lastname: Mourtada
authors.forename: John L
authors.initials: JL
authors.lastname: Horton
mesh_terms: D001918:Brachytherapy / Q000379:methods*; D002857:Chromium / Q000494:pharmacology*; D003035:Cobalt / Q000494:pharmacology*; D003327:Coronary Disease / Q000628:therapy; D023903:Coronary Restenosis / Q000473:pathology; D006801:Humans; D009010:Monte Carlo Method; D010761:Phosphorus Radioisotopes; D011874:Radiometry / Q000379:methods*; D012984:Software; D013997:Time Factors
chemical_list: D010761:Phosphorus Radioisotopes; D002857:Chromium; D003035:Cobalt