Radiation therapy uses high-energy beams of subatomic particles to kill cancer cells. According to the American Cancer Society, radiation therapy for colon cancer may be used before or after surgery, and with or without chemotherapy.
How it Works
According to the Radiological Society of North America, radiation therapy destroys the cell's ability to divide, which stops tumors from growing. The body then naturally eliminates the damaged cells, shrinking the tumor.
Types of Radiation
The American Cancer Society says five types of radiation therapy are used for colon and rectal cancers. External beam radiation is delivered by a machine outside the body called a linear accelerator. Internal radiation, called brachytherapy, is delivered by tiny radioactive pellets, or "seeds," that are implanted next to or into the tumor. Cavitary radiation, used for rectal cancer, is delivered by a radiation-emitting probe the doctor inserts into the rectum. Microsphere radiation uses tiny balls coated with radiation about one-third the diameter of a human hair. These spheres are infused into a major artery and are then carried by the blood to the tiny arteries serving the tumor where they lodge, cutting off the blood supply to the tumor and emitting radiation that kills the cells.
Standard Radiation Treatment in Colon Cancer
The National Comprehensive Cancer Network, or NCCN, which develops clinical practice guidelines for standard cancer treatments, says radiation therapy should be considered in conjunction with chemotherapy for advanced stage cancer with a T4 tumor. This means a pathologist has examined the surgically removed tumor and found that it has grown beyond the wall of the colon or rectum and penetrated adjacent tissues. In cases where the tumor has spread to the liver, but not elsewhere, the NCCN says microsphere radiation may be used in patients whose cancer has been shown to be resistant to chemotherapy.
Other Radiation Treatments for Colon Cancer
According to the National Cancer Institute, early stages of colon or rectal cancer are usually not treated with radiation, and patients with moderate to advanced stages of cancer, stages II through IV, may be offered radiation therapy as part of their treatment plan but only through clinical trials. This means there is not yet enough evidence to support the use of radiation therapy as a standard therapy for colorectal cancer. Radiation may be offered when the cancer has not responded to chemotherapy or has recurred but has not previously been treated with radiation.
Palliative Radiation Treatment for Colon Cancer
In patients with advanced colon or rectal cancer where treatment to cure the disease is no longer possible, the American Cancer Society says doctors may give radiation to relieve cancer symptoms. Such use of radiation is called palliative radiation, and it is used when the patient is not healthy enough to undergo surgery or chemotherapy. Radiation in this situation is used to control tumors that may be causing intestinal blockages, bleeding or pain.
Side Effects
According to the American Cancer Institute, side effects of radiation therapy for colon and rectal cancer include: nausea and inflammation of the rectum or colon, which can cause diarrhea or painful bowel movements and blood in the stool. Depending on where the radiation treatment is directed, there can also be bowel incontinence and bladder irritation, which can cause frequent urination, burning sensations or blood in the urine. The skin can also experience irritation at the site where the radiation beam is directed. Some men and women can also experience sexual dysfunction. Side effects usually go away after treatment is completed.
References
- American Cancer Society: Treating Colon/Rectum Cancer Topics Radiation Therapy
- Radiological Society of North America: Introduction to Cancer Therapy
- National Comprehensive Cancer Network Clinical Practice Guidelines in Oncology v.3.2010: Colon Cancer Principals of Radiation pg. 35.
- National Cancer Institute: Colon Cancer Treatment, Treatment Option Overview
