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.
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
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
Palliative radiation therapy
In addition to the main use of radiation therapy to help stop or cure cancer, it can also be used to treat symptoms. This is known as palliative radiation therapy, which can help to reduce tumor size and lessen the pain caused by tumors, for example.7
Quality of life may also be improved by radiation therapy for someone who has developed, for example, bone cancer secondary to another form of cancer that has spread, such as bowel, breast or prostate cancer.7
While the cancer will not be cured by the radiation treatment, it can help to stop the formation of further painful bone cancers, and help to reduce the pain caused by weakened bone (by strengthening it and preventing further weakening).7
Radiation therapy is not always suitable for palliative use, and when it is used, it is often accompanied by other forms of cancer treatment and palliative care.7
Other examples of palliative radiation therapy include the following (see Cancer Research UK for even more detailed information):7
- Relieving pressure or blockage by reducing tumor size
- Treating symptoms of brain cancer, such as headaches, nausea and dizziness
- Reducing symptoms of lung cancer, such as chest pain and breathlessness
- Controlling ulcerating tumors - the therapy can reduce or even help to heal wounds caused by tumors, while also helping to control bleeding and infections
- Shrink a specific obstruction caused by a tumor, known as a superior vena cava obstruction (SVCO); head and neck tumors can cause a blockage, affecting the return of blood to the heart.
Side effects of radiation therapy
Radiation therapy does not discriminate between cancer cells and healthy cells, although cancer cells are more vulnerable to the effects of treatment.6,8
Radiation therapy affects cancer cells more than healthy ones because of a higher rate of cell replication and a poorer capacity for self-repair in cancer cells. Some healthy cells are also affected by radiotherapy, however, leading to the side effects of radiation therapy.6,8
Side effects differ according to the part of the body treated and the type and dose of radiation therapy used, among other factors such as the patient's general level of health.3,4,6,8-10
Short-term side effects of radiation therapy
Short-term or acute adverse effects of radiation treatment can include the following:3,4,6,8-10
- Fatigue or lethargy - feeling tired or lacking energy
- Local irritation to the skin, causing it to look red, swollen, blistered, sunburned or tanned
- Other effects specific to the treated location, such as hair loss, urinary problems or gastrointestinal symptoms, including nausea, vomiting and diarrhea
- Also depending on location, tissue inflammation such as esophagitis (inflammation of the food pipe), pneumonitis (lungs) and hepatitis (liver)
- A drop in the number of white blood cells or platelets, although this is uncommon.
Long-term side effects of radiation therapy
Just as the possible short-term side effects listed above depend on various factors such as the treatment site and the dose given, the possible long-term side effects of radiation therapy also depend on these factors. These long-term effects can include:4,8,10-13
A possible side effect of radiation therapy to the neck is a stiff jaw.
- Stiffening and restricted movement as a result of tissue scarring (fibrosis) - after neck therapy, for example, when the jaw can stiffen. Exercises may be advised after cancer surgery and radiation therapy
- Skin effects - such as delayed wound healing and a spidery red or purple appearance (similar to telangiectasias) caused by dilated capillary blood vessels
- Diarrhea and bleeding as a result of bowel damage when the abdomen is irradiated
- Hormone problems (endocrinopathies) - such as hypopituitarism or hypothyroidism, dry mouth (xerostomia), memory loss, sterility
- 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, however, than the risk of a new cancer caused by radiation therapy.
Again, the particular risks are related to the area treated, so not all of the above examples are likely or even possible with every mode of radiation therapy. The likelihood of getting any one of the longer-term side effects is highly dependent on the individual. Patients should, therefore, receive guidance from their health care team about the balance of risks and benefits when considering radiation therapy.
Radiation dose, monitoring and protection
Doses of radiation are measured in terms of the amount of energy absorbed per kilogram of body mass exposed - 1 joule of energy deposited in 1 kilogram of mass amounts to 1 international unit of energy absorbed, or 1 gray (Gy).2
Doctors giving radiation therapy keep a record of the amount of radiation administered and the area of the body exposed.3
Both the individual doses and the cumulative dose affect the risk of long-term side effects, and different cancers and areas of the body respond in different ways.3
Health professionals delivering radiation or working in the vicinity of treatment are required to take steps to keep their exposure to a minimum and to measure how much they receive.
Like any medical treatment, a patient makes the decision to go ahead with the care team's recommendation for radiation therapy having determined for themselves that the potential benefits outweigh the potential risks.3
Radiation treatment planning
Radiation treatment planning is designed to ensure that the radiation therapy will have maximum benefits with minimal potential risk. This involves working out an exact site, angle of radiation, dose, and so on.4
Radiographers are just one of the many health care professionals involved in the planning of radiation therapy.
For example, in radiation therapy planning for breast cancer, patients undergo simulation sessions during which a tumor is scanned and analyzed, and marks are made on the skin with ink or tattoo - all contributing to the best delivery of the real therapy later on.7,14
Radiation planning can be a detailed process involving a number of health care workers, including doctors (oncologists and specialist radiologists), nurses, radiographers and other technicians.
Just as side effects depend on the individual patient's circumstances, so too do the exact form of radiation therapy and the planning for it. The planning will:7,14
- Reflect the type, position and size of the cancer, and whether the tumor is close to radiation-sensitive tissues or organs
- Take into account the depth to which the radiation will need to penetrate to reach the target, and consider the patient's general health and clinical history.
- Usually involve CT scanning, but sometimes make of less sophisticated X-ray imaging, or MRI and PET scans.
- Occasionally involve the use of contrast mediums or other markers that help to define tumors, and inks or tattoos and molds or masks that help to pinpoint the radiation target.
Modern radiation planning is usually computer-assisted and sophisticated and powerful enough to produce 3D images of tumors.7,13
In an effort to further minimize potential risks of radiotherapy by making treatment even more targeted and effective, researchers are investigating the possibility of harnessing the immune system to fight cancer cells. By combining radiation treatment with medications that prompt immune system activity, it may be possible to induce anti-tumor immunity.14