Proton Therapy With Capecitabine for Rectal Cancer

Inclusion Criteria:

1. All patients must have clinical stage T4 or recurrent adenocarcinoma of the rectum. Patients will be regarded as having clinical stage T4 if there is evidence of invasion of other structures on one or more of the following: endorectal ultrasound, pelvic CT, and physical examination, including pelvic examination
2. Histology must be confirmed with review by the Department of Pathology at UT MD Anderson Cancer Center.
3. All patients must have no distant metastatic disease in the liver, peritoneum, lungs, or paraaortic lymph nodes.
4. Patients must have a performance status (Karnofsky scale) of 70% or greater, and be able to tolerate the proposed radiation and chemotherapy regimen.
5. There are no age restrictions for this protocol.
6. Patients must have WBC \> 4000 cells/mm\^3, platelets \> 150,000/mm\^3, total serum bilirubin \< 2 mg/dl, BUN \<30 mg/dl, creatinine \< 1.5 mg/dl and creatinine clearance \> 50cc/min (estimated as calculated with Cockcroft-Gault equation).
7. Patients must have signed informed consent indicating that they are aware of the investigational nature of the study, and are aware that participation is voluntary. Patients must sign a study-specific consent form, which is attached to this protocol.

Exclusion Criteria:

1. Prior radiotherapy to the pelvis.
2. Pregnant or lactating woman. Woman of childbearing potential with either a positive or no pregnancy test at baseline. Woman / men of childbearing potential not using a reliable and appropriate contraceptive method. (Postmenopausal woman must have been amenorrheic for at least 12 months to be considered of non-childbearing potential). Patients will agree to continue contraception for 30 days from the date of the last study drug administration. Sexually active males must practice contraception during the study.
3. Treatment for other carcinomas within the last five years, except cured non-melanoma skin and treated in-situ cervical cancer.
4. Patients with uncontrolled intercurrent illness including, but not limited to, ongoing or active infection, cardiac disease NYHA class III or IV, unstable angina pectoris, unstable cardiac arrythmia or tachycardia (heart rate \> 100 beats/minute), poorly controlled hypertension (systolic blood pressure \> 160 mm Hg or diastolic blood pressure \> 100 mm Hg) or psychiatric illness/ social situations that would limit compliance with the study requirements are excluded.
5. Other serious uncontrolled medical conditions that the investigator feels might compromise study participation.
6. Major surgery within 4 weeks of the start of study treatment, without complete recovery.
7. Prior unanticipated severe reaction to fluoropyrimidine therapy or known hypersensitivity to 5-fluorouracil or capecitabine.
8. Patients on coumadin must be changed to Lovenox at least 1 week prior to starting capecitabine. Low dose (1 mg) coumadin is allowed.
9. Aluminium hydroxide and magnesium hydroxide-containing antacids such as Maalox must be stopped during this study.
10. Patients \</= 18 years.