Neoadjuvant Accelerated Short Course Radiation Therapy With Proton Beam and Capecitabine for Resectable Pancreatic Cancer

* Not everyone who participates in this research study will receive the same schedule of radiation therapy. The schedule of radiation therapy will depend on the number of participants enrolled on the study and how well they have tolerated their radiation schedule. All patients will receive proton beam therapy. * Here are the proposed schedules of radiation therapy. If at any point too many subjects experience too many unacceptable side effects, no subject will be enrolled to the next level. Dose Level 1: 10 radiation sessions given Monday-Friday for two weeks. Dose Level 2: 5 radiation sessions given Monday, Wednesday and Friday in Week 1 and Tuesday and Thursday in Week 2. Dose Level 3: 5 radiation sessions given Monday, Tuesday, Thursday and Friday in Week 1 and Monday in Week 2. Dose Level 4: 5 Radiation sessions given Monday through Friday in Week 1. * In Dose Levels 2, 3 and 4, there are fewer radiation sessions, but the radiation dose given at each session is slightly higher than the dose given in each of the 10 sessions of Dose Level 1. * Capecitabine will be given orally (pill form) starting on the first day of radiation therapy and will be taken for the two weeks that the participant receives radiation therapy. * On days 1, 8 and 15 of each study cycle, the participant will be seen at the clinic for: physical examination, questions about side effects; and routine blood tests. * After the last day of study treatment there will be up to a six-week rest period before surgery is performed. * About three to six weeks after the participant has finished study treatment, the following procedures will be done: CT or MRI, physical examination; questions about side effects and blood tests.