In this paper, we present a fast and robust collision detection algorithm for bifurcated stent graft simulation. The algorithm is designed for simulating bifurcations of Y-stents in blood vessels in CT-data. For stent simulation, we use the active contours method (ACM) which realizes internal and external forces acting on the stent. The internal forces are for the elastic and smoothing behavior of the stent surface. The external forces (balloon force and resistance of the vessel wall) pull and push the stent towards the artery wall. In addition to these two forces, another force interacts in the bifurcated part of the stent. For this purpose, the algorithm uses axis aligned bounding boxes (AABB) that are placed along these bifurcated parts. Our simulation and collision detection algorithm is evaluated on computed tomography angiography (CTA) data with variations in anatomy and location of pathology.