This phase I trial studies the side effects and best dose of radiosurgery boost following chemoradiation in treating patients with locally advanced pancreatic cancer that may or may not be removed by surgery. Drugs used in chemotherapy work in different ways to stop the growth of tumor cells, either by killing the cells or by stopping them from dividing. Radiation therapy uses high-energy x-rays to kill tumor cells. Radiosurgery can send x-rays directly to the tumor and cause less damage to normal tissue. Giving chemotherapy and radiation therapy together with radiosurgery may kill more tumor cells and allow doctors to save the part of the body where the cancer started