A medical system is disclosed that has three basic components； a retractable sheet, a first balloon that has a centrally arranged hollow, and a collapsible/expandable support structure at the hollow. The first balloon is for instance mounted/molded onto the exterior surface of the support structure. The aggregate of support structure and the first balloon is positioned, and once the sheet has been retracted from the first balloon, the first balloon is inflated. The support structure may be self-expandable or expandable by an expansion unit, such as a further balloon arranged at its inside. The lumen of the support structure is chosen to be smaller than that of a main lumen. The outside diameter of the inflated first balloon is chosen to be larger than the interior diameter of the main lumen. This procedure may be done using standard Seldinger technique and fluoroscopy. This makes the system user friendly and increases patient safety, as a well established clinical method may be used with some modifications according to the invention.
