Rectal Cancer
For cancers of the rectum and anus, radiation therapy often does more than treat the disease — it can preserve normal bowel function that surgery alone would take.
About rectal cancer
Cancers that begin in the colon, rectum or anus are grouped together as colorectal cancers, and together they are the third most commonly diagnosed cancer among men and women. This page focuses on the rectum and the anal canal — the last few inches of the bowel.
Location changes the treatment. Because the rectum and anus sit low in the pelvis, surrounded by structures that control continence, the goal is to treat the cancer thoroughly while keeping as much normal function as possible. That is where radiation therapy earns its place.
For anal cancers in particular, surgery is less likely to be the main treatment. Radiation therapy combined with chemotherapy can often clear the disease while preserving healthy organs and tissue, so that you continue to have bowel movements normally. Depending on the stage, surgery may still be necessary. Surgery for the anal canal removes the area responsible for bowel movements and usually requires a colostomy, which reroutes bowel movements to a bag outside the body.
Some bowel cancers are hereditary. If you or a family member has been diagnosed with a colorectal cancer — especially before age 50, or alongside several other cancers in the family — other relatives should be screened.
Signs and symptoms
Symptoms in this part of the bowel are easy to mistake for hemorrhoids or a passing stomach problem. If something has changed and has not resolved, have it looked at.
- Bleeding from the rectum, or blood in the stool
- A change in bowel habits that lasts more than a few weeks
- Narrow or ribbon-like stools
- A feeling of fullness or that the bowel does not empty completely
- Pain, itching or a lump around the anus
- Unexplained weight loss or fatigue
When to call
These symptoms have many possible causes, most of them not cancer. But they are worth a conversation. If something has changed and hasn't resolved, contact your primary care physician — early evaluation is what makes treatment straightforward.
How we treat it
Rectal and anal cancers are treated with radiation therapy, chemotherapy and surgery, frequently in combination. Radiation delivers concentrated beams to the rectum, anal canal and pelvis, destroying cancer cells in the treated area. Compared with other approaches it is relatively protective of healthy organs and tissue, because normal cells can repair radiation damage in a way cancer cells cannot. Your physician will evaluate you first and then explain which combination fits your case.
External Beam Radiation Therapy
The main form of radiation used for rectal and anal cancers. A series of daily treatments delivers radiation accurately to the pelvis from a linear accelerator. It may be given before surgery to shrink a tumor, after surgery to clear what remains, or in place of surgery alongside chemotherapy.
Chemoradiation for Organ Preservation
Radiation given together with chemotherapy is the standard approach for most anal cancers and for many rectal cancers. Treating the disease this way can make removing the anus unnecessary, which means keeping normal bowel movements rather than needing a colostomy. Whether this is possible in your case depends on the stage and location of your tumor.
Intensity Modulated Radiation Therapy (IMRT)
IMRT varies the strength of the beam across the treatment field so a high dose reaches the tumor while nearby bladder, bowel and skin receive less. In the pelvis, where sensitive structures sit close together, this precision translates directly into fewer side effects.
Image Guided Radiation Therapy (IGRT)
Images are taken at the treatment machine each day, right before treatment, to confirm the target is where the plan expects it. Organs in the pelvis shift slightly from one day to the next, and IGRT accounts for that shift instead of assuming it away.
3-D Conformal Radiation Therapy (3-D CRT)
Uses CT imaging to build a three-dimensional model of the tumor so the beams can be shaped to its contours. Your radiation oncologist will tell you which of these techniques your plan uses and why.
What treatment involves
Treatment starts with a planning session that maps the area to be treated, usually with a CT scan. Landmarks are placed on your skin, often as tiny tattoos, so the radiation therapists can position you identically at every appointment.
The dose and schedule vary from person to person, but treatment is commonly delivered five days a week, Monday through Friday, over the course of several weeks. Spacing the treatments this way delivers enough radiation to destroy tumor cells while giving healthy cells time to recover between sessions.
Each session takes only a few minutes and is painless. If chemotherapy is part of your plan, your medical oncologist will coordinate its schedule with your radiation appointments so the two work together.
Possible side effects
Side effects are usually temporary and typically resolve shortly after treatment ends. Tell your care team about any discomfort — managing it is part of the treatment, not an interruption to it.
- Fatigue that builds through the weeks of treatment
- Diarrhea, cramping or more frequent bowel movements
- Soreness or irritation of the skin around the anus
- Bladder irritation, or burning with urination
- Nausea or reduced appetite
- Irritation of the vagina or discomfort with intercourse
Caring for yourself during treatment
- Rest when you need to, and don't hesitate to ask for help.
- Follow your care team's advice — and ask when anything is unclear.
- Tell us about every medication, vitamin and supplement you take.
- Eat a balanced diet and drink plenty of fluids.
- Treat skin in the treatment area gently: no sun, no hot or cold packs, and only lotions your team has approved.
- Lean on support groups, family and friends. Coping is part of treatment.
Trusted resources
- Colon Cancer Alliance — www.ccalliance.org
- Fight Colorectal Cancer — www.fightcolorectalcancer.org
- American Cancer Society — www.cancer.org
- RT Answers (American Society for Radiation Oncology) — www.rtanswers.org
Clinical background adapted from materials by the American Society for Radiation Oncology (rtanswers.org) and the American Cancer Society.
Cancers We Treat
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Talk with a board-certified radiation oncologist about whether radiation therapy belongs in your treatment plan.