Endovascular brachytherapy for the prevention of restenosis after angioplasty.

Restenosis is an unsolved clinical and financial limitation of angioplasty. Local irradiation is a new approach for the reduction of restenosis. Several animal studies have demonstrated the effective inhibition of arterial neointimal proliferation by percutaneous or endovascular irradiation. High-dose-rate irradiation from gamma and beta sources can be applied from radioactive wires or seeds and from liquid beta-emitter-filled balloon catheters. Dosimetric calculations have been performed for all relevant radionuclides. An effective dose can be applied within 10 min to the treated arteries. Beta-emitters are characterized by a low tissue penetration, which simplifies radiation protection but complicates the achievement of a homogeneous dose distribution without centering of the irradiation source. Gamma-emitters are characterized by deep tissue penetration and delivery of almost the same dose to all vessel layers; however, considerable care with regard to radiation protection of the environment is required if gamma-emitters are used. The liquid-filled balloon ensures a homogeneous dose delivery due to the self-centring irradiation source but entails the possibility of radioactivity incorporation in the event of balloon rupture. The most attractive radionuclide for this purpose is rhenium-188, which is available from the 188W/188Re generator system. Radiation exposure after accidental incorporation can be limited by chelation with mercaptoacetyltriglycine or by subsequent oral administration of perchlorate. Initial clinical trials have demonstrated the feasibility of the various irradiation techniques and yielded encouraging results. The use of unsealed radioactivity in a balloon catheter involves the nuclear medicine physician in this new field of therapy. This review discusses the concepts, the radiotracers and the results of animal experiments and early clinical trials in the field of endovascular irradiation employed as a possible means to prevent restenosis after angioplasty.