Experimental therapeutics and clinical studies in (re)stenosis

Initial studies with gamma radiotherpay to inhibit coronary restenosis

BACKGROUND

Early studies indicate brachytherapy is a potential clinical treamtent for restenosis after coronary angioplasty procedures. The objective of this study was to evaluate the safety and efficacy of gamma radiation plus stenting in patients' previous restenosis.

METHODS

In patients with previous coronary restenosis, balloon dilatation and/or coronary stenting was undertaken and then patients were randomly assigned to receive either Iridium-192 or placebo. Quantitative coronary angiographic, intravascular ultrasonographic, and clinical follow-up was obtained.

RESULTS

Of the 55 patients enrolled, 26 were treated with Iridium-192 and 29 were in the placebo group. Late luminal loss was significantly lower in the treated group compared to the placebo group (0.38 +/- 1.06 mm vs. 1.03 +/- 0.97 mm, p = 0.03). Restenosis (stenosis of > or = 50% at follow-up) was found in 17% of treated patients compared to 54% of placebo patients (p = 0.01). The need for target lesion revascularization was observed in 12% of patients in the treated group compared to 45% in the placebo group (p = 0.01).

CONCLUSIONS

In this initial trial, at 12 months follow-up, patients with previous restenosis were benefited by catheter-based gamma radiation therapy.

[Role of intravascular brachytherapy in the prevention of vascular restenosis after angioplasty]

About 30% of patients who underwent percutaneous transluminal coronary angioplasty show evidence of restenosis, which appears to be independent of the angioplasty method used. The restenosis is due of two factors, firstly migration of smooth vascular muscle cells of the vascular media to the intima and multiplication which lead to the formation of a neo-intima. Irradiation limits the proliferation by acting of the cells in the mitotic stage. The vascular target volume is not very thick and is difficult to define it, that why brachytherapy seems to be the best procedure to prevent restenosis. However, the development of this treatment present many difficulties. Different irradiation techniques have been studied. Such techniques include catheter containing radioactive sealed source, radioactive stent, or balloon containing radioactive liquid inside. Each of these methods have their own advantages, inconveniences, problems and risks. Radioisotope may be either beta or gamma emitters. Gamma emitter presents problems for radioprotection but the satisfactory dose distribution may be difficult to obtain using beta emitter. Choice of dose, dose rate and delay between the end of angioplasty and the beginning of brachytherapy is subject to some discuss. Animal experiments using radioisotope have shown reduction in cell proliferation. Human trials showed feasibility, safety of the method and real impact on restenosis prevention. However, long-term efficacy has not been proved because the follow-up of the patients is too short. A randomized trial of 192Ir brachytherapy for prevention of restenosis has recently shown the efficacy in short and median term. However, long term efficiency and secondary effects have not yet been established as the follow up time of this study is still too short. That is why, collaboration between cardiologists and radiotherapists and physicists is indispensable to enable the development of an optimal technique.

Catheter-based radiotherapy to inhibit restenosis after coronary stenting

BACKGROUND

In animal models of coronary restenosis, intracoronary radiotherapy has been shown to reduce the intimal hyperplasia that is a part of restenosis. We studied the safety and efficacy of catheter-based intracoronary gamma radiation plus stenting to reduce coronary restenosis in patients with previous restenosis.

METHODS

Patients with restenosis underwent coronary stenting, as required, and balloon dilation and were then randomly assigned to receive catheter-based irradiation with iridium-192 or placebo. Clinical follow-up was performed, with quantitative coronary angiographic and intravascular ultrasonographic measurements at six months.

RESULTS

Fifty-five patients were enrolled; 26 were assigned to the iridium-192 group and 29 to the placebo group. Angiographic studies were performed in 53 patients (96 percent) at a mean (+/-SD) of 6.7+/-2.2 months. The mean minimal luminal diameter at follow-up was larger in the iridium-192 group than in the placebo group (2.43+/-0.78 mm vs. 1.85+/-0.89 mm, P=0.02). Late luminal loss was significantly lower in the iridium-192 group than in the placebo group (0.38+/-1.06 mm vs. 1.03+/-0.97 mm, P=0.03). Angiographically identified restenosis (stenosis of 50 percent or more of the luminal diameter at follow-up) occurred in 17 percent of the patients in the iridium-192 group, as compared with 54 percent of those in the placebo group (P= 0.01). There were no apparent complications of the treatment.

CONCLUSIONS

In this preliminary, short-term study of patients with previous coronary restenosis, coronary stenting followed by catheter-based intracoronary radiotherapy substantially reduced the rate of subsequent restenosis.