H I Amols1, F Trichter, J Weinberger. 1. Columbia University, Department of Radiation Oncology, and Departments of Medicine and Pharmacology, New York, NY, USA. amolsh@mskcc.org
Abstract
BACKGROUND: Intravascular irradiation with beta-emitters has been proposed for inhibition of restenosis in coronary arteries after balloon angioplasty or stent implantation. Previous studies have shown the effectiveness of gamma-radiation to prevent recurrent restenosis, even in the presence of an implanted stent. The limited range of beta-particles compared with gamma-radiation, however, opens the question of whether absorption and scattering of beta-particles by stent struts will cause significant perturbations in the uniformity and magnitude of the radiation dose, which may in turn compromise treatment. METHODS AND RESULTS: Nine different stents were deployed with a balloon filled with a beta-emitting radioactive liquid. Dose distributions were measured with Gafchromic film. Stents varied significantly in their absorption of beta-particles. Some stents, constructed of fine meshed wires, produced minimal dose perturbations. Others, with thicker, high-atomic-number struts, induced cold spots in the dose distribution adjacent to the wires of </=35%. Average dose reduction varied from 4% to 14% in the presence of various stents. CONCLUSIONS: Radiation strategy may have to be tailored to stent design. Stents that minimally perturb the dose distribution may be deployed before irradiation. Those that significantly alter the radiation dose might be better deployed after irradiation. Dose prescriptions may require modification if such perturbations prove clinically significant. Observed dose perturbations, however, decreased rapidly with increasing distance from the stent, which may mitigate the clinical impact of these findings. This, as well as the effects of stents on gamma-dose distributions, requires further investigation.
BACKGROUND: Intravascular irradiation with beta-emitters has been proposed for inhibition of restenosis in coronary arteries after balloon angioplasty or stent implantation. Previous studies have shown the effectiveness of gamma-radiation to prevent recurrent restenosis, even in the presence of an implanted stent. The limited range of beta-particles compared with gamma-radiation, however, opens the question of whether absorption and scattering of beta-particles by stent struts will cause significant perturbations in the uniformity and magnitude of the radiation dose, which may in turn compromise treatment. METHODS AND RESULTS: Nine different stents were deployed with a balloon filled with a beta-emitting radioactive liquid. Dose distributions were measured with Gafchromic film. Stents varied significantly in their absorption of beta-particles. Some stents, constructed of fine meshed wires, produced minimal dose perturbations. Others, with thicker, high-atomic-number struts, induced cold spots in the dose distribution adjacent to the wires of </=35%. Average dose reduction varied from 4% to 14% in the presence of various stents. CONCLUSIONS: Radiation strategy may have to be tailored to stent design. Stents that minimally perturb the dose distribution may be deployed before irradiation. Those that significantly alter the radiation dose might be better deployed after irradiation. Dose prescriptions may require modification if such perturbations prove clinically significant. Observed dose perturbations, however, decreased rapidly with increasing distance from the stent, which may mitigate the clinical impact of these findings. This, as well as the effects of stents on gamma-dose distributions, requires further investigation.