A standard treatment for pancreatic cancer is radiation therapy plus chemotherapy after surgery. Radiation therapy and chemotherapy are commonly given for up to six weeks. Previous research has suggested that giving the radiation and chemotherapy for a shorter amount of time (accelerated schedule) before surgery may be better tolerated. In this research study, different schedules of proton radiation therapy will be used. Each schedule will give about the same total dose of radiation. However, the total dose will be spread out over different time periods and different numbers of sessions. The purpose is to find the shortest schedule of radiation therapy that can be given without unacceptable side effects. Proton beam radiation is being used because of its unique ability to deposit its energy directly in the tumor, resulting in less radiation to normal tissue. A new type of PET scan is also being studied to see if it can help predict the response to pre-surgery treatment.