It is estimated that 135,430 Americans will be diagnosed with colon cancer this year. Colorectal cancer is the third most commonly diagnosed cancer in men and women. Of those, 39,910 will be diagnosed with rectal cancer. Patients with these types of cancer often benefit from radiation therapy as part of treatment. Some cancers involving the bowel happen within families (hereditary colorectal cancers). It is important to discuss your diagnosis with family members so they can decide with their doctors whether they need to be screened for colorectal cancers. This is especially important if you were diagnosed with a colorectal cancer at a young age or if there are several other types of cancers that run in your family.
Radiation therapy is often used in conjunction with surgery and chemotherapy to treat cancers of the colon, rectum and anus. Treatment involves focused radiation to the bowel and pelvis to treat cancer cells in the area.
Surrounding healthy tissue can be affected, but normal cells are often better able to heal from radiation injury, compared to cancer cells, because normal cells have maintained the ability to repair radiation-induced damage.
Surgery often plays a key role in treatment. For colorectal cancers, it is the main curative treatment. The surgeon will determine how much of the large bowel needs to be removed, but often it involves removal of a section of the colon. Because the tumor can spread to lymph nodes nearby, often some lymph nodes are removed at the time of surgery. Depending upon the location of the tumor, surgery may or may not allow normal bowel function afterwards.
For anal cancers, surgery is less frequently used at the time of diagnosis because effective organ-preserving approaches are available. If bowel function is poor, sometimes surgery is used at first, but often it is reserved as a second chance for cure where organ-preserving treatment does not succeed. Because surgery for the anal canal involves removing the area responsible for how you go to the bathroom, a surgery called a colostomy to re-route bowel movements is usually necessary as well.
While surgery and radiation focus directly on treating the bowel or pelvic area, medication is often recommended to improve cure rates. A medical oncologist will evaluate you and determine what medications may be most helpful.
External beam radiation therapy involves a series of daily outpatient treatments that accurately deliver radiation to the area needing therapy. The radiation beam usually comes from a machine called a linear accelerator or linac.
Before beginning treatment, you will be scheduled for a simulation to map out the area to be treated. This will involve having X-rays and/or a CT scan. Landmarks placed on your skin (often tiny tattoos) allow the radiation therapists delivering your treatments to precisely position you each day.
To minimize side effects, the treatments are usually given over about five or six weeks, five days a week (Monday through Friday). This allows your doctors to get enough radiation into your body to kill the tumor cells while giving healthy cells time to recover each day.
Technical terms that may be mentioned for colorectal and anal cancer treatments include 3-dimensional conformal radiation therapy (3-D CRT) and intensity modulated radiation therapy (IMRT). Your radiation oncologist can provide more information about these different techniques.
It is important to care for yourself as well as possible during radiation therapy.
Completing treatment and recovery can be challenging. Seek out help from support groups and friends ahead of time. If you have a support network in place before and during treatment, it will be easier to get through side effects since people you can count on will be around to help you. If you need additional support, let your doctor and nurse know.
© American Society for Radiation Oncology, 2019.