Vascular irradiation for the prevention of restenosis after angioplasty: A new application for radiotherapy
Year: 1996
Type: editorial
Abstract: In stark epidemiologic terms, heart disease remains the leading cause of death in the United States, representing the underlying cause of mortality in roughly one third of all deaths. The most recent annual figures available from 1992 indicate 717,706 deaths from heart disease compared to 520,578 deaths from cancer (4). The principal disease process involved in cardiac morbidity and mortality is atherosclerosis resulting in stenotic coronary lesions and ischemic cardiomyopathy. Percutaneous transluminal angioplasty (PTCA) was developed as a less invasive treatment of coronary artery disease as compared to surgical revascularization. In this technique, a balloon is placed within a stenotic lesion and temporarily expanded within the artery. This results in a controlled dissection of the intima and media of the artery as well as compression of the atherosclerotic plaque, yielding an increase in intraluminal cross-sectional area and improved blood flow. With approximately 400,000 angioplasties performed annually in the United States currently, this procedure to a Iarge extent, has supplanted coronary artery bypass grafting. A major limitation of angioplasty is the occurrence of restenosis in 30%-50% of cases over 6 months (5,7). The pathophysiology of restenosis is complex and incompletely understood, but involves inflammatory responses, thrombosis, elastic recoil of the arterial wall, long-term vessel remodeling, and intimal-neointimal hyperplasia. A variety of pharmacologic treatments to prevent restenosis have been disappointing. One somewhat successful strategy to combat restenosis has been postangioplasty intravascular stern placement. Several randomized studies have shown a statistically significant decrease in restenosis rates to 22%-32% (2,6). Other trials of stenting are ongoing, and it remains possible that restenosis rates will be further reduced by improved angioplasty techniques. Despite stenting, neointirual hyperplasia still occurs and may in fact be stimulated by stenting in some circumstances. Moreover, not all coronary lesions are anatomically suitable for stenting (e.g., at a vessel bifurcation). Thus, at the present time restenosis remains a significant medical problem. The economic impact of restenosis in the United States has been estimated at somewhere between 800 million and 2 billion dollars/year. Given this magnitude, it is not surprising that there is tremendous interest within the academic community and the medical marketplace for treatments of restenosis. A novel therapeutic approach to restenosis under active investigation has been to administer radiotherapy to a vascular lesion after angioplasty. Similar to the treatment of keloids, the infiltration of inflammatory cells, myofibroblasts, and fibroblasts into a wound is attenuated. Accumulating experimental evidence using either brachytherapy or external beam radiotherapy suggests that this is a feasible and efficacious approach and that modest doses of radiation on the order of 10-30 Gy (minimal dose) to the target lesion is required (3). Compared to external beam therapy, the dose from brachytherapy is better localized to the intended target and better clinical results have been observed by a number of groups. Two types of brachytherapy techniques have been used: one type using a catheter-based radiation delivery system, the other using radioactive stent implantation. Catheter-based therapy has been employed with either 19’Ir sources, which emit photons; or 90Sr, ‘“Y, or “P sources, which emit p particles. Stents have used radioactive “P. Traditionally, with brachytherapy, the dose to a target is specified at a distance of 1 cm from the source. At this reference distance, the dosimetry of brachytherapy sources is reasonably well established. The intended target for irradiation in intravascular brachytherapy is much smalfer, however, in the range of l-3 mm. At these short distances, the dosimetry is somewhat uncertain because of steep gradients and requires further study. Another potential source for uncertainty is that at short distances, there may be significant contributions from low energy secondary radiations, such as fluorescent X rays, ,8 or N particles, secondary electrons, and so forth, which are absorbed within the first few millimeters of irradiation either in source encapsulation
Authors: Ravinder Nath, Kenneth B. Roberts
Institution: Yale University
Language: English
Subfield: Surgery
Field: Medicine
Domain: Health Sciences
Open Access status: hybrid
Estimated APC paid: $4,130
OpenAlex ID: W2085513177