Rectal and anal cancers that have come back after external beam radiation therapy are usually treated with a big surgery that involves the creation of a colostomy (bag worn outside the body to collect waste). However, not all patients can have or want this surgery. Brachytherapy (the placement of a radioactive source in or near cancer tissue) is an alternative treatment for these patients. High-dose-rate brachytherapy uses a higher dose of radiation than conventional brachytherapy (which doesn’t always work to prevent cancer recurrence), but doctors are not certain how high a dose can be safely used.
The purpose of this study is to find the highest dose of radiation that can be used in high-dose-rate brachytherapy without causing too many side effects in patients with rectal or anal cancer that has returned after external beam radiation therapy. Patients will also receive chemotherapy (either orally, as capecitabine, or intravenously, as 5-fluorouracil).