Radiation therapy treats cancer by using high doses of radiation to kill cancer cells and shrink tumors. These high-energy rays are targeted toward the location of tumors in an effort to localize its effects. Though radiation is rarely used to treat colorectal cancer by itself, it is sometimes used simultaneously with chemotherapy. When radiation and chemotherapy are used in conjunction with each other, this is typically called chemoradiation or chemoradiotherapy.

Radiation works by killing cancer cells by damaging their DNA, rendering them unable to continue dividing indefinitely. Once these damaged cancer cells die, the immune system can then break down the cells.

When radiation is used in the treatment of colorectal cancer, it is typically used in conjunction with other treatment methods. When used with surgery, radiation therapy is typically used to shrink tumors to make them easier to remove, or to kill lingering cancer cells during or after surgery. Radiation is used alongside chemotherapy when a patient isn’t healthy enough for surgery, to treat cancer that has spread to other areas of the body, or palliatively,  to ease symptoms of advanced stage cancer.

Radiation Therapy for Colon Cancer 

Radiation therapy is not often used to treat colon cancer unless it is in the treatment of tumors that have grown next to or into other organs, to improve your quality of life, or to improve outcomes of surgery. Uses of radiation therapy to treat colon cancer include:

• Shrink tumors before surgery to make it easier to remove
• Intraoperative Radiation Therapy (IORT): Kill lingering cancer cells during surgery
• Kill lingering cancer cells after surgery
• Treat a person who is not healthy enough for surgery, along with chemo
• Treat cancer that has metastasized to other areas of the body
• Improve the quality of life of patients with advanced stage cancer causing intestinal blockages, bleeding, or pain

Radiation Therapy for Rectal Cancer 

Radiation therapy is more often used to treat rectal cancer in comparison to colon cancer, and it is used in similar ways – to treat tumors that have grown next to or into other organs, to improve your quality of life, or to improve outcomes of surgery. Uses of radiation therapy to treat rectal cancer include:

• Shrink tumors before surgery to make it easier to remove, especially if tumors are located in an area that is difficult to operate
• Intraoperative Radiation Therapy (IORT): Kill lingering cancer cells during surgery
• Kill lingering cancer cells after surgery
• Treat a person who is not healthy enough for surgery, along with chemo
• Treat cancer that has metastasized to other areas of the body
• To treat recurring tumors in the pelvis after radiation has been used
• Improve the quality of life of patients with advanced stage cancer causing intestinal blockages, bleeding, or pain

Advantages & Disadvantages of Radiation Therapy

Advantages

• Decreases the chance of tumor recurrence in the pelvis or near the rectum and adjacent lymph nodes by 50%
• Decreases the chance of an operation causing permanent colostomy
• Less toxicity from chemoradiation if done prior to surgery
• Effective, non-invasive, and well-tolerated for treating metastatic colorectal cancer

Disadvantages

• Can cause new mutations to be created or new antigens to be expressed
• Dying tumor cells release antigens and pro-inflammatory cytokines
• Removes immunosuppressive immune cells
• Inconvenience (e.g. in some cases radiation must be delivered daily)
• Can cause poor wound healing if surgery is performed after radiation therapy

Types of Radiation Therapy

The two main types of radiation therapy are defined by the method that radiation is delivered – externally or internally. External-beam radiation therapy is delivered by a machine aimed at the location of your tumor. Internal radiation therapy is delivered by a radiation source that is put inside the body in solid or liquid form.

External-beam Radiation Therapy (EBRT)

External-beam radiation therapy uses a machine to deliver radiation to where the cancer is located. Radiation treatment is usually given five days a week for several weeks. It may be given in the doctor’s office or at the hospital.

Stereotactic Radiation Therapy

Stereotactic radiation therapy is a type of external-beam radiation therapy that may be used if a tumor has spread to the liver or lungs. This type of radiation therapy delivers a large, precise radiation dose to a small area. This technique can help save parts of the liver and lung tissue that might otherwise have to be removed during surgery. However, not all cancers that have spread to the liver or lungs can be treated in this way.

Intraoperative Radiation Therapy

Intraoperative radiation therapy uses a single, high dose of radiation therapy given during surgery.

Brachytherapy

Brachytherapy is the use of radioactive “seeds” placed inside the body. In one type of brachytherapy with a product called SIR-Spheres, tiny amounts of a radioactive substance called yttrium-90 are injected into the liver to treat colorectal cancer that has spread to the liver when surgery is not an option. Limited information is available about how effective this approach is, but some studies suggest that it may help slow the growth of cancer cells.

Radiation Therapy for Rectal Cancer

For rectal cancer, radiation therapy may be used before surgery, called neoadjuvant therapy, to shrink the tumor so that it is easier to remove. It may also be used after surgery to destroy any remaining cancer cells. Both approaches have worked to treat this disease. Chemotherapy is often given at the same time as radiation therapy, called chemoradiation therapy, to increase the effectiveness of the radiation therapy.

Chemoradiation therapy is often used in rectal cancer before surgery to avoid colostomy or reduce the chance that the cancer will recur. One study found that chemoradiation therapy before surgery worked better and caused fewer side effects than the same radiation therapy and chemotherapy given after surgery. The main benefits included a lower rate of the cancer coming back in the area where it started, fewer patients who needed permanent colostomies, and fewer problems with scarring of the bowel where the radiation therapy was given.

Radiation therapy is typically given in the United States for rectal cancer more than five weeks before surgery. However, for certain patients (and in certain countries), a shorter course of five days of radiation therapy before surgery is appropriate and/or preferred.

A newer approach to rectal cancer is currently being used for certain people, called total neoadjuvant therapy (TNT). TNT is a novel approach for locally advanced rectal cancer (LARC), which attempts to deliver both systemic chemotherapy and neoadjuvant chemoradiotherapy prior to surgery. With TNT, both chemotherapy and chemoradiation therapy are given for about six months before surgery. This approach is still being studied to determine which patients will benefit most.

It is important to remember that all people are different, and while the treatments listed here are the standard of care, doctors will monitor and work as partners with their patients toward the best outcome. If you have any questions or concerns, always be sure to speak with your doctor.

What to Expect from Radiation Therapy

Your ability to carry on normal activities depends on the type of radiation therapy being administered and its frequency. Depending on the schedule of your radiation therapy, you may be required to stay at the hospital. Some patients may be able to perform normal daily activities, like working full-time or part-time, without much interruption, while others may be too fatigued. Side effects from radiation therapy typically go away after treatment in a few weeks or a few months.

Over the course of your lifetime, there is a limit to the amount of radiation you can be exposed to. If you have had radiation therapy in the past, you may not be eligible to receive radiation to the same area of your body if you’ve reached your safe lifetime dose of radiation. However, if you have already reached your lifetime limit in one are of your body, you may be eligible to receive radiation therapy again targeted toward another area.

Radiation Therapy Side Effects

Radiation only affects the area of the body where it is administered (except in the case of systemic radiation therapy). Thus, radiation therapy for colorectal cancer should not cause hair loss, unless radiation is administered to the scalp. However, when given locally, radiation can also damage or kill nearby healthy cells that can cause negative side effects. Most side effects disappear after treatment

• Skin irritation at the site of radiation exposure (redness, blistering, or peeling)
• Nausea
• Fatigue
• Hindered wound healing if administered before surgery
• Rectal irritation (diarrhea, painful bowel movements, or blood in the stool)
• Bowel incontinence
• Bladder irritation (frequent urination, burning or pain, blood in the urine)
• Sexual problems (such as erectile dysfunction or vaginal irritation)
• Changes in menstruation
• Infertility
• Scarring or fibrosis that cause tissues to stick together

More Treatment Resources

Radiation therapy is only used to treat colon and rectal tumors under certain circumstances, and usually used in conjunction with other colorectal cancer treatments. Find out more about colorectal cancer chemotherapy and colorectal cancer surgery. 

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