Intravascular radiation for the prevention of recurrence of restenosis in coronary arteries

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Abstract
Despite the use of new technology and adjunctive pharmacological therapy, in-stent restenosis continues to hamper the outcome of approximately 150,000 patients who undergo stented coronary angioplasty in the US annually. While coronary stenting eliminates elastic recoil and vessel contracture by acting as a mechanical scaffold within the vessel, it is unable to inhibit excessive neointimal formation and may actually promote it. For years, the growth-inhibiting properties of ionising radiation have been used successfully to control benign proliferative disorders. Based on this experience, vascular brachytherapy, the intravascular delivery of radiation, was viewed as a viable solution to inhibit neointimal hyperplasia. A series of studies performed in animal models identified the mechanisms by which radiation may reduce restenosis. Data from these studies showed that endovascular radiation reduces restenosis by inhibiting cell proliferation and by inducing favourable remodelling. The success of these initial studies led to several double-blind, multicentre, placebo-controlled, randomised, clinical trials evaluating intravascular radiation, with either gamma- or beta-radiation sources, proved to be an effective solution for the prevention of neointimal proliferation and restenosis. However, an increased rate of late thrombosis in patients who had received intracoronary radiation did evolve from the initial use of this therapy. Prolonged antiplatelet therapy and a reduction in the number of new stents placed at the time of radiation has been shown to minimise these complications. Other concerns that still need to be resolved include edge effect and geographical miss. Intravascular brachytherapy is currently the only approved therapy for this complex disease. It is clear that there are still on-going concerns that will eventually be clarified when the long-term results from ongoing clinical trials around the world become available.