Dosimetric effect of source centering and residual plaque for beta-emitting catheter based intravascular brachytherapy sources

Catheter-based radiation delivery systems employing both beta -particle and gamma -ray emitters are currently being investigated for their efficacy in addressing restenosis following percutaneous coronary intervention (PCI). The dosimetric consequences of source centering within the arterial lumen a nd presence of residual plaque are potentially important issues for the uni form delivery of dose to the arterial tissue. In this study, we have examin ed the effect of source centering on the resulting dose to the arterial wal l from clinical intravascular brachytherapy sources containing P-32 and Sr- 90/Y-90. Monte Carlo simulations using the MCNP code were performed for the se catheter-based sources with offsets of 0.5 mm and I mm from the center o f the arterial lumen in homogenous water medium as well as in the presence of residual plaque. Three different positions were modeled and the resultin g dose values were analyzed to assess their impact on the resulting dose di stribution. The results indicate a variation ranging from -40% to +70% for P-32 source and -30% to +50% for Sr-90/Y-90 at a radial distance of 2 mm fr om the center of the coronary artery, relative to the dose from a centered source, for a 0.5 rum offset. The variation for a I mm offset ranges from - 65% to +182% for P-32 source and to -50% to + 140% for Sr-90/Y-90. A concen tric residual plaque layer was also modeled so as to assess the combined in fluence of offset and residual plaque on the dosimetry. Finally the effect of cardiac motion and its potential impact on catheter position and hence t he dose distribution is also examined by considering two separate cases of catheter displacement. The results indicate that dose variations range betw een -28% to +91% when it is assumed that cardiac motion causes catheter mov ement during coronary lesion irradiation. (C) 2001 American Association of Physicists in Medicine.