The purpose of this study is to see what amount of radiation is safe to give to rectal or anal cancer patients who are being treated with a procedure called brachytherapy.

Inclusion Criteria:

• Histologically or cytologically confirmed locally residual or recurrent cancer of the rectum or anus

• Prior pelvic EBRT

• Age > or = to 18 years

• ECOG performance status 0, 1, or 2

• At least 4 weeks from prior major surgery or radiotherapy

• Have undergone Surgical, Medical and Radiation Oncology evaluations to confirm :

  • Eligible for infusional 5-FU or capecitabine
  • Will not undergo surgery for the study disease
  • Able to receive HDR brachytherapy ANC ≥ 1.5 cells/mm3 and PLT ≥100,000/mm3

• Adequate Renal function: Creatinine <1.5 x the upper limit of normal (ULN) or calculated creatinine clearance of ≥ 50cc/min

• Adequate Hepatic functions: Bilirubin less than 1.5 mg/dL; (except in patients with Gilbert's Syndrome, who must have a total bilirubin less than 3.0 mg/dL)

• AST or ALT <3xULN, or <5x ULN if known liver metastases

• Normal Cardiac function:

  • No active coronary artery disease;
  • No New York Heart Association class II, III or IV disease;
  • No arrhythmia requiring treatment
  • Maximum tumor length of 7 cm at time of brachytherapy treatment start

Exclusion Criteria:

• Women who are pregnant.
• Women of childbearing potential who are unwilling or unable to use an acceptable method to avoid pregnancy for the entire treatment period and after receipt of brachytherapy. Male subjects must also agree to use effective contraception during the treatment period and until 1 year after the completion of brachytherapy.
• Patients with any other concurrent medical or psychiatric condition or disease which, in the investigator's judgment, would make them inappropriate candidates for entry into this study.
• Patients on concurrent anti-cancer therapy other than that allowed in the study.
• Contraindications to general anesthesia