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

Abstract

A model for the description of the near-field dose deposition from a 32p impregnated 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 consisting of a series of layers of different materials. It is shown that, for each point source originating from the stent surface, the DPK function for water can be scaled consistently along the path through the different layers of material to predict the dose at a given point in the heterogeneous medium. Radiochromic film dosimetry on actual 32p stents is used to test the new model. The experimental setup consists of a water-equivalent phantom in which a stent is deployed and on which a thin layer of polytetrafluoroethylene (PTFE) is deposited to simulate the presence of plaque. Layers of radiochromic films stacked over the phantom are used to measure the dose at distances varying from approximately 0.1 mm to approximately 3 mm from the stent surface with and without PTFE. It is shown that the proposed new DPK model for a heterogeneous medium agrees very well with the experimental data and that it compares favorably to the usual homogeneous DPK model. These results indicate that the new model can be used with confidence to predict the dose in a realistic artery in the presence of plaque.

Off‐label use of medical products in radiation therapy: Summary of the Report of AAPM Task Group No. 121a)

“…The first medical products to show significant results in a clinical trial for the reduction in in-stent restenosis following balloon angioplasty were intravascular brachytherapy sources, although they were eventually superseded to a great extent by drug-eluting stents. During the development stages of IVBT, the radiation sources used in the coronary vessel clinical trials included seed trains ͑with 16,17 and without [18][19][20][21][22] interseed spacing͒, wires, 23-37 radioactive stents, [38][39][40] radioactive liquid filled balloons, 41-43 radioactive gas filled balloons, 44 and balloons impregnated with radioactivity. 45,46 In addition there were peripheral vascular trials 47 using a HDR…”

A dosimetry and radiobiological model for intravascular brachytherapy treatment planning with radioisotope emitting stents

“…Nevertheless, stents have not been entirely successful in eliminating restenosis due to tissue proliferation, and have actually been found to stimulate neointimal hyperplasia in 20-30% of the cases within six to twelve months following angioplasty (Fox, 2002). In-stent restenosis remains problematic, particularly in smaller vessels and longer lesions (Janicki et al, 1999) with rates ranging anywhere from 31-50% as reported by several animal and clinical studies (Fischell et al, 2000).…”

“…The dose distribution generated by the beta particles emitted from the radioisotope was computed at distances ranging from 0.1 to 3 mm from the stent surface. A later study by Janicki et al (1999) introduced a new model taking into account the scaling property of the dose point kernel function which can be extended to a heterogeneous medium with a density different to that of water. Because in a realistic artery the presence of plaque can allow attenuation of the beta particles, incorporating plaque density in a theoretical model has some advantageous effects.…”

“…Several investigators have used the dose point kernel for calculation of 3D dose distribution of radioactive stents (Prestwich, et al., 1995;Duggan et al, 1998;Janicki et al, 1997Janicki et al, , 1999. The dosimetry model is equipped for the calculation of absorbed dose at any specified point defined radially and longitudinally from the surface of the stent.…”

“…With DPK, this becomes much more difficult, as the DPK describes the dose emitted by an isotropic point source in water. However, calculations have been done using a scaling factor of DPK that takes into account different densities such as that of plaque surrounding an artery (Janicki et al, 1999).…”