Dose model for a beta-emitting stent in a realistic artery consisting of soft tissue and plaque

A model for the description of the near-field dose deposition from a P-32 i mpregnated stent in an arterial system consisting of soft tissue and dense plaque is presented. The model is based on the scaling property of the dose -point-kernel (DPK) function which is extended to a heterogeneous medium co nsisting of a Series of layers of different materials. It is shown that, fo r each point source originating from the stent surface, the DPK function fo r water can be scaled consistently along the path through the different lay ers of material to predict the dose at a given point in the heterogeneous m edium. Radiochromic film dosimetry on actual P-32 stents is used to test th e new model. The experimental setup consists of a water-equivalent phantom in which a stent is deployed and on which a thin layer of polytetrafluoroet hylene (PTFE) is deposited to simulate the presence of plaque. Layers of ra diochromic films stacked over the phantom are used to measure the dose at d istances varying from similar to 0.1 mm to similar to 3 mm from the stent s urface with and without PTFE. It is shown that the proposed new DPK model f or a heterogeneous medium agrees very well with the experimental data and t hat it compares favorably to the usual homogeneous DPK model. These results indicate that the new model can be used with confidence to predict the dos e in a realistic artery in the presence of prague. (C) 1999 American Associ ation of Physicists in Medicine. [S0094-2405(99)00511-8].