Colorectal cancers include cancers of the large intestine (colon), rectum and anus.

Over 150,000 people in the US are diagnosed with colon cancer each year. It is the third most common cancer in both men and women.

Patients with colorectal cancers are treated by a team of physicians that may include the following:

A colorectal or general surgeon may perform a biopsy or surgical removal of the cancer. A radiation oncologist is a physician who is trained to use radiation therapy to treat cancer.

A medical oncologist is a physician trained to use chemotherapy to treat cancer.

The treatment of colorectal cancer varies depending on the site, the extent (or stage) and the patient’s overall health.

Colon cancer is usually treated with surgical removal. Depending on the extent of the disease, chemotherapy my be recommended after surgery. Radiation therapy is usually not done.

Rectal cancer is usually treated with a combination of surgery, radiation therapy and chemotherapy. Depending on the findings, surgery may be done first, or after a course of radiation therapy and chemotherapy.

Anal cancer is usually treated with a combination of radiation therapy and chemotherapy. Surgery is not usually done.

Radiation Therapy for Colorectal Cancer

External beam radiation therapy is a series of high energy x-ray treatments delivered on a linear accelerator. The treatments are generally given daily, Monday through Friday, over several weeks. The daily treatments last about 15 to 20 minutes, and are painless.

Prior to beginning treatment, a planning session is done to define the area that needs to be treated. Usually this will involve having a CT scan done in the treatment position. Other studies, such as PET scans, MRIs or CT scans may be used to help the radiation oncologist identify the area of tumor involvement.

3-dimensional conformal radiation therapy and intensity modulated radiation therapy (IMRT) are often used to minimize the radiation dose to normal structures while still targeting the area of tumor involvement with high doses of radiation.

Side Effects of Radiation Therapy

Radiation side effects depend on what part of the body is being treated. For patients with colorectal cancers, the pelvic area is usually treated, but treatment may also involve the groin regions, or the anus.

Radiation side effects are cumulative, that is they slowly increase with each passing week of treatment. Most patients experience some fatigue which begins around the second or third week of treatment, and increases until the radiation therapy is completed. Diarrhea, urinary frequency or burning, vaginal discharge are other common side effects. Skin irritation occurs if the anus or groin regions are treated. Typically these sides effects resolve within a few weeks after treatment ends.

Your doctor will review specific side effects with you depending on your particular situation and the treatment required.