Radiation therapy, also known as radiotherapy, is a treatment used against cancer and, less commonly, thyroid disease, blood disorders and noncancerous growths. The treatment owes its existence to a combination of the scientific disciplines of physics and biology.
Radiation can form part of curative or palliative treatments against tumors. Use this page for easy-to-follow information about radiation therapy.
Contents of this article:
Although radiation therapy is also sometimes used for nonmalignant disease, including benign tumors and inflammatory conditions, this page is devoted to its use in treating cancer, as this is its main medical application.
At the end of some sections there are introductions to recent developments that have been covered by MNT's news stories. Also look out for links to information about related conditions, particularly the specific types of cancer treated with radiation therapy.
Fast facts on radiation therapy
Here are some key points about radiation therapy. More detail and supporting information is in the body of this article.
- An estimated 60% of cancer patients in the US receive radiation therapy treatment at some point.
- Radiation therapy is occasionally used to address nonmalignant disease.
- Radiation therapy involves delivering waves of energy sufficient to disrupt the ability of cancer cells to grow and divide; this can kill cancer cells, slow down their growth and shrink tumors to enable surgery.
- Various forms of radiation are used - high-energy X-rays, for example, are used in some forms of external radiation therapy.
- The source of radiation can also be short-range and delivered internally, such as radioactive metal placed in or near cancerous tissue.
- Radiation therapy for cancer can be used alone or in combination with surgery or chemotherapy.
- Radiation therapy can offer relief from cancer symptoms by shrinking a tumor and relieving pressure on surrounding tissues, for example.
- Side effects of radiation therapy occur because adjacent healthy tissue is affected as well as the cancerous tissue, albeit to a lesser extent.
- Most side effects are localized to the area treated and are usually short-term, although some effects, such as fatigue, can be systemic.
- To ensure accurate placement of radiotherapy, the treatment is often simulated during planning before the real treatment is administered.
What is radiation therapy?
As a general term, radiation means waves of energy, such as light or heat. The form of radiation used in cancer therapy is known as ionizing radiation - a high-energy form of radiation. Scientists have named it ionizing radiation because it has enough energy to remove electrons from atoms, thus forming ions.1,2
Exactly how radiation works as a treatment for cancer is complex and still being researched, but the simple description is that it breaks up the DNA of cancer cells in such a way as to disrupt their growth and division, and even kill them.3,4
External beam radiation therapy is typically administered using a linear accelerator.
There are two forms of radiation therapy:
- External beam radiation therapy - the beam of radiation is focused by an external machine onto the treatment area
- Internal radiation therapy (such as brachytherapy) - a radioactive substance is placed in or close to the cancerous tissue.
A machine called a linear accelerator is usually used in external beam radiation therapy to emit X-rays within a specific energy range. Other machines are also available, with these using other forms of energy, including electrons, protons (as in proton therapy) and gamma rays, or a combination.4-6
The idea is that different forms of external beam radiation therapy have specific effects that best suit the particular tumor. High-energy X-rays, for example, are able to reach deeper neoplasms. Advances are continually being achieved in the way external beams "narrow in" on their target for best effect and least risk.4
External beam radiation therapy is the more commonly used form of radiotherapy, and the main focus of the information on this page. Brachytherapy - introduced in the next section - is a more recent development and is used, for example, in prostate cancer treatment.
Internal radiation therapy
Brachytherapy is a form of internal radiation therapy. It involves introducing low-energy radioactive metal that has a short range. This means it exerts its effects in a localized area to disrupt nearby cancer cells.4-6
Highly radioactive material can be temporarily placed in or near the tissue - held in a tube, for example, and then removed, or less radioactive brachytherapy seeds can be left in place permanently, with their radioactivity gradually dropping off to zero.4,6 Between these two types of brachytherapy, there are also radioactive wires that may be left in place for a number of days.7
Brachytherapy presents a low risk of radiation exposure for people around the patient, although health workers need to be shielded from their repeated exposure to patients and the high concentrations of source material used. The risk from treated patients is not high because the radioactivity has such a short range.4,6
Radiation used in medicine is dangerous only when precautions are not taken - if health workers do not shield themselves from repeated exposure, for example.
The risk is much higher during rapid periods of human development, however. Patients undergoing internal radiation therapy should temporarily avoid contact with children and anyone who is pregnant, which also means that children and pregnant people are nor normally allowed to visit the patient in hospital during treatment.4,6
Radioactive liquid is used in other forms of internal radiation therapy. This liquid is swallowed or received by injection, and these treatments are also administered under carefully controlled conditions for safety.5,7
Radioactive iodine is used as a treatment for thyroid cancer, and bone cancer may be treated with radioactive forms of strontium, phosphorus or radium.7
Side effects of internal radiation therapy can be similar to those of external radiation therapy, as discussed on the next page. There may also be additional specific symptoms related to the location of the therapy and/or the physical trauma and short-term local pain caused by insertion of seeds or wires.7
In prostate cancer brachytherapy, for example, there may be soreness and bruising in the groin following treatment, and for around a month there may be pain or difficulty associated with passing urine.7
Recent developments in radiation therapy from MNT news
Low-dose-rate prostate brachytherapy may improve survival compared with dose-escalated external beam radiotherapy, found a randomized trial presented in April 2015.
Radiation therapy for women with early-stage breast cancer may be less toxic given as a shorter course at higher doses than a longer course at lower doses, suggested studies in JAMA Oncology in August 2015. A quality-of-life advantage was also shown.
A study published in The Lancet in September 2014 found that radiotherapy applied to the chest appears to have benefits for survival and lower recurrence of small cell lung cancer.
Guidelines recommend that older women with early-stage breast cancer should not be given radiation therapy, but an analysis published in the journal Cancer in December 2014 found they were not being followed.
When is radiation therapy used?
The Radiological Society of North America estimates that around 60% of cancer patients receive radiation therapy as part of their treatment at some point.6
Cancers that can be particularly suitable for radiation therapy aimed at curing the disease are those that are well-defined and confined. This allows the whole area of cancerous tissue to be targeted by the radiation.8 In contrast, some forms of cancer - leukemia or lymphoma, say - can be treated with total body irradiation.7
Radiation therapy can also be used to reduce symptoms, caused by tumor growth, for example. In such instances, radiotherapy is termed palliative radiation therapy.
Radiation therapy for cancer may be deployed:5,6,8
- Alone - against prostate cancer or a tumor of the larynx, for example, when radiation may be preferable to surgery
- Alongside surgical treatment - before a cancer operation (to shrink the tumor), during it, or afterward (to reduce the risk of incomplete removal of cancer cells)
- With drug treatment, chemotherapy - a combination that can reduce the need for surgery.
One example of a situation where radiation therapy may be preferable to surgery is early-stage laryngeal tumor. Radiation offers an alternative to the removal of the vocal chords, avoiding surgical damage while having a similar efficacy as surgery.
Radiation therapy can be used alongside both chemotherapy and surgery. Sarcomas, or tumors of the breast, esophagus, lung or rectum may be treated with all three modalities.8
On the next page, we look at when radiation therapy is used for symptoms and give information about the side effects of radiation therapy.