Preliminary Results of Gamma-I Trial, Multi-institution Double Blind Prospective Randomized Study Evaluating the Efficacy of IR-192 to Reduce Coronary In-stent Restenosis

Theodore Robnett, MD
OncoLink Assistant Editor
Last Modified: November 1, 1999

Presenter: Prabhakar Tripuraneni, M.D.
Affiliation: Scripps Clinic

Summary:
One of the major disadvantages of coronary angioplasty is the high rate of re-stenosis in the months following the procedure. Single arm endovascular brachytherapy trials have yielded encouraging results suggesting decreased re-stenosis with minimal toxicity after this treatment.

Methods:
This study enrolled 252 patients from 12 centers in a randomized trial comparing Ir-192 seed ribbons versus placebo in patients with in-stent re-stenotic lesions of native coronary arteries. Lesion diameter was 2.75 to 4.0 mm and up to 45 mm in length. The minimum dose to the farthest external elastic membrane (EEM) was 800 cGy, while the maximum to the closest EEM was less than 3000 cGy. Average vessel diameter and lesion length in both arms were similar. Eighty-six per cent of patients underwent angiogram at 6 months from treatment.

Results:

There was a 41% decrease in restenosis in the Ir-192 arm (p < 0.003), and a 36% decrease in major adverse cardiac event (death, myocardial infarction, or need for re-vascularization) in the IR-192 arm (p < 0.01) at 6 months follow up.
Those who underwent angiogram at 6 months post-treatment in the Ir-192 arm had a re-stenosis rate at the reference diameter which was decreased by 59% compared with patients in the placebo arm (p < 0.001).
A dose-response relationship was also observed, with patients receiving 8 Gy at 2 mm having a 60% chance of re-stenosis, and patients receiving >14 Gy at 2 mm having a 20% chance of re-stenosis.

Clinical/Scientific Implications:

This is the first multi-center randomized trial to verify statistically significant reduction in patients at risk for restenosis.
These results verify previous single institution randomized series and show promise for this therapeutic modality.
Short term feasibility and efficacy were demonstrated, although long term follow-up is necessary before making definitive conclusions regarding overall re-stenosis rate and toxicity of coronary endovascular brachytherapy.

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