Radiation Therapy and Capecitabine With or Without Curcumin Before Surgery in Treating Patients With Rectal Cancer

Inclusion Criteria: * All patients must have clinical stage T3,4 N0,1,2 or T2N1,2 adenocarcinoma of the rectum; patients will be clinically staged using endorectal ultrasound, pelvic computed tomography (CT) or magnetic resonance imaging (MRI), and physical examination * Histology must be confirmed with review by the Department of Pathology at MD Anderson Cancer Center (MDACC) * All patients must have no distant metastatic disease in the liver, peritoneum, lungs, or paraaortic lymph nodes * Patients must have a performance status (Karnofsky scale) of 70% or greater * Absolute neutrophil count (ANC) \> 1200 cells/mm\^3 * Platelets \> 100,000/mm\^3 * Total serum bilirubin \< 2 mg/dl * Blood urea nitrogen (BUN) \< 30 mg/dl * Creatinine \< 1.5 mg/dl or creatinine clearance \> 50cc/min (estimated as calculated with Cockcroft-Gault equation) * 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 also agree to refrain from use of additional herbal supplements during the course of the study * 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 * Postmenopausal woman must have been amenorrheic for at least 12 months to be considered of non-childbearing potential Exclusion Criteria: * Prior complete course up to 5 Gy of radiotherapy to the pelvis * Pregnant or lactating woman; women of childbearing potential who have not undergone a hysterectomy with either a positive or no pregnancy test at baseline; women / men of childbearing potential not using a reliable and appropriate contraceptive method (oral, injectable, or implantable hormonal contraceptive; tubal ligation; intra-uterine device; barrier contraceptive with spermicide; or vasectomized partner) * Treatment for other carcinomas within the last five years, except cured non-melanoma skin and treated in-situ cervical cancer * Patients with uncontrolled intercurrent illness including, but not limited to, ongoing or requiring IV antibiotics, cardiac disease New York Heart Association (NYHA) class III or IV, unstable angina pectoris, unstable cardiac arrhythmia or tachycardia (heart rate \> 100 beats/minute), or psychiatric illness/ social situations that would limit compliance with the study requirements are excluded * Other serious uncontrolled medical conditions that the investigator feels might compromise study participation * Major surgery within 4 weeks of the start of study treatment * Prior unanticipated severe reaction to fluoropyrimidine therapy or known hypersensitivity to 5-fluorouracil or capecitabine or curcumin * Concurrent use of Coumadin other than low dose (1 mg) Coumadin used for line patency; patients on Coumadin must be changed to Lovenox at least 1 week prior to starting capecitabine * Concurrent use of cimetidine, allopurinol, or aluminium hydroxide and magnesium hydroxide-containing antacids such as Maalox * Sorivudine and brivudine use within 4 weeks of the start of study treatment