<qa>  What is a common clinical condition caused by various malignancies?Malignant biliary obstruction is a common clinical condition caused by various malignancies. Currently,biliary stent implantation guided either by fluoroscopy or endoscopy has become the most important methods for relieving malignant biliary obstruction. However, the benefit for the survival of the patients with palliation of the stent treatment is limited because no therapeutic effects on process of the tumor itself by a stent implantation. Encouraged by the success of 125I esophageal stent in esophageal carcinoma, a novel biliary stent loaded with 125I radioactive seeds has been developed in our institute. After ex vivo and in vivo evaluations for the delivery system, the investigators prospectively compare the responses to treatment with this radiation biliary stent, versus the conventional biliary SEMS in patient with malignant biliary obstruction. 