Brachytherapy might be used to treat some rectal cancers, but more research is needed to understand how to best use and when to use brachytherapy.
For this treatment, a radioactive source is put inside your rectum next to or into the tumor. This allows the radiation to reach the rectum without passing through the skin and other tissues of the belly (abdomen), so it's less likely to damage nearby tissues.
Endocavitary radiation therapy: For this treatment, a small balloon-like device is placed into the rectum to deliver high-intensity radiation for a few minutes. This is typically done in 4 treatments (or less), with about 2 weeks between each treatment. This can let some patients, particularly elderly patients, avoid major surgery and a colostomy. This type of treatment is used for some small rectal cancers or in cases where radiation was already given in the pelvic area and the rectal cancer has come back. Sometimes external-beam radiation therapy is also given.
Interstitial brachytherapy: For this treatment, a tube is placed into the rectum and right into the tumor. Small pellets of radioactive material are then put into the tube for several minutes. The radiation travels only a short distance, limiting the harmful effects on nearby healthy tissues. It's sometimes used to treat people with rectal cancer who are not healthy enough for surgery or have cancer that has come back in the rectum. This can be done a few times a week for a couple of weeks, but it can also be just a one-time procedure.
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From the Daily Mail: The Bowel Cancer Operation that means you DON'T need a Colostomy Bag