Portal vein tumor thrombosis (PVTT) is a common paraneoplastic condition in advanced primary hepatocellular carcinoma or hepatobiliary tract malignancies. Tumors with PVTT are frequently associated with adverse and aggressive features such as intrahepatic tumor dissemination, early treatment failure, or deterioration of hepatic function. Therefore, the treatment outcomes for PVTT in historical series are often dismal and discouraging. More recently, beneficial effects and excellent outcomes of external beam radiation therapy (EBRT) for treating this disease have been reported, and the use of EBRT is becoming more common because of the non-invasive nature of RT and rapid advances in RT technology. We hope to be able to cure this devastating condition in the near future with more advanced and efficacious disease management strategies. The current status and clinical trial results for EBRT as a promising treatment option for managing PVTT will be discussed here.