Stereotactic Body Radiation Therapy After Chemotherapy for Unresectable Perihilar Cholangiocarcinoma

This trial is studying whether giving targeted radiation (SBRT) after chemotherapy to people with a bile duct cancer near the liver (perihilar cholangiocarcinoma) that cannot be surgically removed can extend survival. **You may be eligible if...** - You have been diagnosed with perihilar cholangiocarcinoma (a bile duct cancer near the liver) that cannot be removed with surgery - Your diagnosis has been confirmed by biopsy or imaging - You are eligible to receive gemcitabine-based chemotherapy - Your case has been reviewed by a liver tumor specialist team **You may NOT be eligible if...** - Your cancer has spread to distant organs - You are not able to tolerate chemotherapy or radiation - You have serious liver problems beyond what is caused by the tumor - You are pregnant or breastfeeding Talk to your doctor to see if this trial is right for you.