Residual plaque burden, delivered dose, and tissue composition predict 6-month outcome after balloon angioplasty and β-radiation therapy

Background-Inhomogeneity of dose distribution and anatomic aspects of the atherosclerotic plaque may influence the outcome of irradiated lesions after balloon angioplasty (BA). We evaluated the influence of delivered dose and morphological characteristics of coronary stenoses treated with beta-radiation after BA. Methods and Results-Eighteen consecutive patients treated according to the Beta Energy Restenosis Trial 1.5 were included in the study. The site of angioplasty was irradiated with the use of a beta-emitting Sr-90/Y-90 source. With the side branches used as anatomic landmarks, the irradiated area was identified and volumetric assessment was performed by 3D intracoronary ultrasound imaging after treatment and at 6 months. The type of tissue, the presence of dissection, and the vessel volumes were assessed every 2 mm within the irradiated area. The minimal dose absorbed by 90% of the adventitial volume (D(v90)Adv) was calculated in each 2-mm segment. Diffuse calcified subsegments and those containing side branches were excluded. Two hundred six coronary subsegments were studied. Or those, 55 were defined as soft, 129 as hard, and 22 as normal/intimal thickening. Plaque volume showed less increase in hard segments as compared with soft and normal/intimal thickening segments (P<0.0001). D(v90)Adv was associated with plaque volume at follow-up after a polynomial equation with linear and nonlinear components (r=0.71; P=0.0001). The multivariate regression analysis identified the independent predictors of the plaque volume at follow-up: plaque volume after treatment, D(v90)Adv, and type of plaque. Conclusions-Residual plaque burden, delivered dose, and tissue composition play a fundamental role in the volumetric outcome at 6-month follow-up after beta-radiation therapy and BA.