A subgroup analysis of the Scripps Coronary Radiation to Inhibit Proliferation Poststenting Trial

INTRODUCTION: In the Scripps Coronary Radiation to Inhibit Proliferation Poststenting (SCRIPPS) Trial, 192Ir significantly reduced angiographic, ultrasonographic, and clinical endpoints of restenosis. The objective of this analysis was to quantitate the impact of patient, lesion and technical characteristics on late angiographic outcome. METHODS: Patients with restenotic, stented coronary lesions were randomized to receive either 192Ir or placebo sources. Late luminal loss and loss index were calculated for several patient subgroups, including patients with diabetes, in-stent restenosis, multiple previous percutaneous transluminal coronary angioplasty (PTCA) procedures, longer lesion lengths, saphenous vein grafts, small vessel diameters, and minimum dose exposures < 8.00 Gy. Two-factor analysis of variance was used to test for an interaction between patient characteristics and treatment effect. RESULTS: In the treated group, late loss was particularly low in patients with diabetes (0.19 mm), in-stent restenosis (0.17 mm), reference vessel diameters < 3.0 mm (0.07 mm), and patients who received a minimum radiation dose to the entire adventitial border of at least 8.00 Gy. The loss index in each of these subgroups was similarly low at -0.02, 0.03, -0.02, and 0.03, respectively. By 2-factor analysis of variance, a significant interaction between subgroup characteristic and treatment effect (late loss) was found in patients with in-stent restenosis (p = 0.035), and patients receiving a minimum dose of 8.00 Gy to the adventitial border (p = 0.009). CONCLUSION: In this pilot study, patient characteristics associated with a more aggressive proliferative response to injury appeared to confer an enhanced response to radiotherapy. Furthermore, a dose threshold response to 192Ir was found with an enhanced response occurring when the entire circumference of the adventitial border was exposed to at least 8.00 Gy.