Radiation therapy is a treatment used for cancer and, less commonly, thyroid disease, blood disorders, and noncancerous growths.
It can have a targeted, powerful effect on tumors that are confined to a specific area.
Radiation can form part of curative or palliative treatments against tumors. This MNT Knowledge Center article provides easy-to-follow information about radiation therapy.
Although radiation therapy is also sometimes used for nonmalignant disease, including benign tumors and inflammatory conditions, this page focuses on its main medical application in treating cancer.
Fast facts on radiation therapy
Radiation therapy involves delivering powerful waves of energy to disrupt the ability of cancer cells to grow and divide, killing cancer cells, slowing their growth, and shrinking tumors to enable surgery.
The side effects of radiation therapy occur because healthy tissue near the tumor is affected as well as the cancerous tissue. Most side effects are localized to the area treated and usually short-term, although some effects, such as fatigue, can occur body-wide.
To ensure accurate placement of radiation therapy, the treatment is often simulated during planning before the real treatment is administered.
What is radiation therapy?
External beam radiation therapy is typically administered using a linear accelerator.
Radiation therapy uses waves of radiation to treat cancers and tumors, as well as other conditions.
As a general term, radiation means waves of energy, such as light or heat.
The form of radiation used in cancer therapy is a high-energy type known as ionizing radiation.
Exactly how radiation works as a treatment for cancer is complex and still being researched, but on a simple level it breaks up the DNA of cancer cells in a way that disrupts their growth and division and can even kill them.
Radiation therapy will sometimes be used on its own, and in some cases will be used alongside other cancer treatments, such as chemotherapy, if a cancer specialist decides that this will enhance the effect of the treatment.
Approximately 60 percent of people being treated for cancer in the United States will receive radiation treatment.
The side effects of radiation therapy occur when non-cancerous cells are also affected by the treatment.
Radiation therapy reacts in the same way with cancer cells and non-cancerous cells. However, cancer cells are more vulnerable to the effects of treatment, due to cancer cells tendency to copy themselves at a faster rate and repair more slowly.
Some non-cancerous cells are also affected by radiation therapy, however, leading to potentially severe side effects.
Side effects vary based on the part of the body being treated, the overall health of the person receiving radiation therapy, and the type and dose of radiation used.
Short-term side effects
Short-term effects of radiation treatment can include the following:
fatigue or lethargy
skin irritation, including swelling, blisters, and a sunburned or tanned appearance
effects specific to the area of treatment, such as hair loss, urinary problems, nausea, vomiting, and diarrhea
tissue inflammation, such as esophagitis, pneumonitis, and hepatitis
rarely, a drop in the number of white blood cells or platelets
Long-term side effects
Long-term effects also depend on the site of treatment and can include:
Stiffening and restricted movement: After neck therapy, for example, the jaw can stiffen. This can occur as a result of tissue scarring. Exercises may be advised after cancer surgery and radiation therapy to help loosen movement.
Skin effects: These include delayed wound healing and a spidery red or purple appearance caused by dilated capillary blood vessels.
Diarrhea and bleeding: These can occur as a result of bowel damage when the abdomen receives radiation therapy.
Hormone problems: These can include hypopituitarism or hypothyroidism, dry mouth, memory loss, and infertility.
A second cancer caused by radiation exposure: Although rare, soft-tissue sarcoma, for example, can be caused by high doses of radiation. The risk of recurrence of the cancer being treated is higher than the risk of a new cancer being caused by radiation therapy.
Not all of the above examples are likely or even possible with all types of radiation therapy. The likelihood of getting any one of the longer-term side effects depends largely on the individual.
People opting for radiation therapy should, therefore, receive guidance from their healthcare team about the balance of risks and benefits.
Radiation used in medicine is dangerous only when precautions are not taken – if health workers do not shield themselves from repeated exposure, for example.
Radiation therapy and chemotherapy are different cancer treatments. They might be used together, or a doctor may select one or the other depending on the required treatment.
Chemotherapy involves the infusion of cancer-killing substances into the blood using a drip or prescribed medications. Radiation therapy, on the other hand, targets a specific area or tumor.
Before radiation therapy, chemotherapy can help to reduce the size of a tumor, making the targeted radiation therapy treatment more effective.
When it is applied after radiation therapy, it can help to prevent the return of tumors that have been removed. Chemotherapy achieves this by killing cancer cells that have split from the original tumor.
When an oncologist, or cancer specialist, prescribes both radiation therapy and chemotherapy at the same time, it is known as chemoradiation. This can increase the impact of radiation therapy on cancer. However, the side effects can be severe when receiving chemoradiation.
Unlike chemotherapy, radiation is not effective against cancers that have spread to other parts of the body. However, it is more powerful and can have a greater effect when shrinking tumors.
What you need to know about chemotherapy
Find out more about chemotherapy by clicking here.
There are two forms of radiation therapy:
external beam radiation therapy, in which the beam of radiation is focused onto the treatment area by an external machine
internal radiation therapy, such as brachytherapy, in which a radioactive substance is placed in or close to the cancerous tissue in a temporary or permanent implant