Radiation Therapy for Colorectal Cancer

What is radiation therapy?  

Radiation therapy is a cancer treatment that uses high doses of radiation (high-energy particles or waves, similar to x-rays) to kill cancer cells.  

How is radiation therapy used to treat colorectal cancer (bowel cancer)?  

Radiation is a localized treatment, meaning it is directed at a specific area containing a tumor (tumour) or cancer cells and not at all parts of the body. Radiation therapy is used more often in the treatment of rectal cancer but is also used to treat colon cancer.

The goals of radiation treatment can be different from patient to patient. The aim may be to shrink the cancer to make surgical resection (removal) more effective or to kill remaining cancer cells to prevent recurrence or metastasis (spreading of cancer). In the case of palliative radiotherapy, the goal is to shrink tumors to reduce symptoms and improve quality of life.

When radiation is given before surgery, it is called neoadjuvant radiotherapy. When given after surgical removal (resection) of the tumor, it is called adjuvant radiotherapy. When chemotherapy and radiation therapy are combined, it is called chemoradiation and it can be neoadjuvant or adjuvant.

Radiation therapy can also be used during surgery; this is called intraoperative radiotherapy. Intraoperative radiation therapy (IORT) is aimed at the site where the colon or rectal tumor has been removed and is used to kill any remaining cancer cells. IORT allows direct targeting of radiation beams with less radiation exposure to nearby organs.

Radiotherapy may also be a treatment option for metastatic colorectal cancer (mCRC) tumors in bone, lung, brain, and sometimes liver.  

Radiation therapy is planned and managed by specialists trained in radiation oncology. Before treatment begins, you may have imaging such as a CT scan or MRI scan to map out your tumor location, and a simulated radiation session to determine the best body positioning for your treatment plan.

How is radiation used to treat colon cancer?  

Radiotherapy is less common for the treatment of colon cancer than for rectal cancer. It is used in treating advanced colon cancer, like stage III or stage IV. It can be used before surgery to reduce the size of a colon tumor to make it easier to remove. Intraoperative radiation treatment can be used during surgery to kill remaining cancer cells directly at the tumor site. After surgery, radiation is used when the surgeon cannot be certain that all the cancer was removed, such as when the margins around the removed tumor are not clear of cancer or the cancer has stuck to other organs in the abdomen. In patients who are not healthy enough to undergo surgery, radiotherapy can be used along with chemotherapy to help control colon cancer. And radiotherapy can be used for symptom relief of pain, colon blockage by the tumor, or tumor bleeding. Radiotherapy can also be used to help treat metastatic colon cancer that has spread to the brain, lungs, or bones.

How is radiation used to treat rectal cancer?  

Radiotherapy is more common in the treatment of rectal cancer, and is used in stage II, stage III, and stage IV cancer. It can be used before surgery to reduce the size of a rectal tumor to make it easier to remove. Intraoperative radiation treatment can be used during surgery to kill remaining cancer cells directly at the tumor site. After surgery, radiation can be used when the surgeon cannot be certain that all the cancer was removed, such as when the margins around the removed tumor are not clear of cancer or the cancer has stuck to other organs in the pelvis. In patients who are not healthy enough to undergo surgery, radiotherapy can be used along with chemotherapy to help control rectal cancer. And radiotherapy can be used for symptom relief of pain, rectal blockage by the tumor, or tumor bleeding. Radiotherapy can also be used to help treat metastatic rectal cancer that has spread to the brain, lungs, or bones.  

What are the types of radiation treatment used for colorectal cancer?

Radiotherapy for CRC is delivered either externally (external beam radiation therapy) or internally (brachytherapy).  

External beam radiation therapy (EBRT) uses a machine called a linear accelerator to aim high-energy beams into the body at the site of the tumor. EBRT is the most common type of radiotherapy for colorectal cancer. There are several subtypes of EBRT used in CRC treatment. Three-dimensional conformal radiation (3D-CRT) allows delivery of radiation from several different angles to match the shape and size of the tumor. Intensity-modulated radiation therapy (IMRT) similarly allows shaping of the radiation dose to match the tumor and has more precision that reduces the radiation exposure to healthy tissue. Stereotactic body radiation therapy (SBRT) offers precision and highly concentrated radiation doses, and can be called stereotactic radiosurgery when it is used in the brain, though it is not actually a surgical procedure.

EBRT is given as an outpatient, usually over a period of weeks, and each session lasts about 30 minutes (though the radiation itself takes just a few minutes). Radiation does not cause pain or burning as it enters the body. Patients receiving EBRT are not radioactive.

Internal radiation therapy, called brachytherapy, is sometimes used to treat rectal cancer. It involves placing a radiation source inside the rectum rather than delivering radiation through the skin and nearby organs. This is done to reduce radiation exposure to healthy tissue, especially if a patient has already had external radiotherapy in the area before. Most rectal cancer radiation treatment is done as an outpatient, and involves placing the radiation source inside the rectum for a few minutes at each treatment session. Sometimes, a very small radioactive implant, about the size of a grain of rice, is placed in the tissue of the rectum and left there for a period of time. This is called interstitial brachytherapy. Patients with radioactive implants may need to take safety precautions at home after implantation to limit radiation exposure to others.

What are the side effects of radiation therapy for colorectal cancer?

The side effects of radiotherapy depend on where the radiation beams are being directed, the type of radiation therapy, and the dose of radiation. Parts of the body that are near the cancer site can have radiation exposure to healthy tissue, causing side effects. However, fatigue (tiredness) can happen with radiotherapy to any area and is a common side effect.  

For radiotherapy to the colon and/or rectum, side effects include digestive system problems like nausea, diarrhea, blood in the stool, painful bowel movements, or bowel incontinence (leakage of stool).

Radiotherapy can affect the skin that is in the path of radiation beams, causing irritation (dermatitis) or hair loss.  

Because the bladder is located near parts of the colon and rectum, it may be affected by radiation, leading to urinary and bladder problems such as urinating more frequently, pain or burning while urinating, or blood in the urine. Again, because the reproductive organs and sexual organs are nearby, fertility problems and sexual problems are possible side effects of radiotherapy, for both men and women.

When radiotherapy is used to treat metastatic tumors in the bone, lung, and brain, side effects depend on the location of the radiation treatment. Radiation therapy for bone metastases can cause fatigue, skin changes, and other side effects related to the body area of the bone, like the spine, hip, or pelvis. Radiotherapy targeting lung tumors in the chest can cause fatigue, skin changes, cough, and shortness of breath. When brain metastatic tumors are the target, possible radiation side effects include fatigue, hair loss, memory or concentration problems, skin changes, nausea and vomiting, and headache.

Be sure to talk to your healthcare team about any side effects you experience.