Radiation therapy is a treatment for cancer and, less commonly, thyroid disease, blood disorders, and noncancerous growths.

A doctor may recommend radiation for cancer at different stages. In the early stages, radiation therapy can help reduce the size of a tumor before surgery or kill remaining cancer cells afterward. In the later stages, it may help relieve pain as part of palliative care.

One form of radiation treatment involves using a machine that produces a beam of radiation. The beam targets a specific area of the body. Another type involves putting a radioactive substance inside the body, either permanently or temporarily.

In this article, we focus mainly on radiation therapy as a cancer treatment.

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Technicians administer external beam radiation therapy using a linear accelerator.

Radiation therapy uses waves of energy, such as light or heat, to treat cancers and other tumors and conditions. The form of radiation used in cancer therapy is a high-energy type known as ionizing radiation.

Scientists still do not know exactly how radiation works as a treatment for cancer.

They do know, however, that it breaks up the DNA of cancer cells in a way that disrupts their growth and division. In this way, radiation can kill cancer cells, preventing or slowing the spread of the disease.

Sometimes a doctor prescribes radiation therapy alone, but usually, they recommend it in combination with other treatments, such as chemotherapy, surgery, or both.

There are many types of cancer. Learn more here.

Radiation can affect healthy cells as well as cancerous ones. When this happens, a person experiences side effects.

Specific side effects depend on factors such as:

  • the area receiving treatment
  • the person’s overall health
  • the type and doses of radiation

Short term side effects

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Short term side effects radiation therapy include fatigue, skin changes, and nausea.

Short term side effects vary, depending on the part of the body receiving radiation.

They can include:

A 2018 study published in BMJ Open recommends screening for anxiety and depression in people undergoing radiation therapy and offering counseling services to those who may benefit from them.

Long term side effects

Long term side effects also depend on the treatment site.

They include:

  • heart or lung problems, if radiation affects the chest
  • thyroid problems, leading to hormonal changes, if radiation affects the neck area
  • lymphedema, which involves lymph fluid building up and causing pain
  • hormonal changes, including a possibility of early menopause, from radiation in the pelvic area

There is a slight chance that high doses of radiation in certain areas can increase the risk of another form of cancer developing. A doctor will provide more specific information and help with weighing the risks and benefits.

Not everyone who has radiation therapy experiences long term side effects. The risk depends on the doses, the area of treatment, and other individual factors.

Radiation therapy is one of several cancer treatments. A doctor may prescribe these separately or in combination.

As well as radiation, a person may have:

  • surgery
  • chemotherapy
  • hormone therapy
  • targeted therapy

The treatment plan will depend on the type of cancer, among other factors.

When a person receives radiation therapy and chemotherapy at the same time, the doctor may call this “chemoradiation.” It can lead to severe adverse effects.

When cancer is at an early stage, a person may have radiation therapy before surgery, to reduce the size of a tumor. Or, they may have it after surgery to help remove any remaining cancerous cells.

Radiation is only effective in targeted areas. It is less effective when cancer has spread to distant parts of the body.

How effective is chemotherapy? Find out here.

There are two forms of radiation therapy.

External beam radiation therapy

This is the most common type. It involves an external machine emitting a beam of radiation that targets the treatment area.

Different forms are available, depending on the need. High-energy beams, for example, can target cancer that is deeper within the body.

Internal radiation therapy

There are different types of internal radiation therapy. Both involve implanting or introducing a radioactive substance into the body.

Brachytherapy involves inserting a radioactive implant in or close to the cancerous tissue. The implant may be temporary or permanent. Another type of internal radiation therapy involves drinking or receiving an injection of radioactive liquid.

The goal is to limit the extent to which healthy tissue around the cancer is exposed to the radiation. Doctors may recommend this treatment for prostate or ovarian cancer, for example.

A doctor may recommend undergoing both main types of radiation therapy. The decision will depend on:

  • the type of cancer
  • the size of the tumor
  • the tumor’s location, including the types of tissue nearby
  • the person’s age and overall health
  • other treatments

Scientists continue to explore ways of improving radiation techniques to achieve more effective outcomes with the least possible risk.

The doctor will discuss radiation therapy and other options and help weigh the pros and cons. Before treatment starts, they will determine the right type and dosage of radiation.

A person receiving external beam radiation may undergo a CT or MRI scan before treatment. This is to pinpoint the exact location and size of the tumor. A doctor may make a permanent but small mark on the skin to ensure that the radiation therapist will target the beam correctly.

A person may need to wear a plaster cast or use a headrest or another device to ensure that they stay still during treatment. The first session may be a simulation, in which the team runs through the procedure.

Many people have five sessions per week for 3–9 weeks, but this depends on specific factors. Each session lasts for around 15 minutes. Radiation therapy is painless, but there will be damage to surrounding tissue. This is why the treatment occurs on only 5 days per week. The 2-day break allows for some healing.

A person who has internal radiation therapy may require an anesthetic before the doctor can implant the radioactive substance. Overall, several sessions and some time in the hospital may be necessary.

The details of the process depend on the type of radiation therapy and the type and location of the cancer.


After receiving external treatment, a person can go home and continue with their daily routine.

However, they may experience:

  • tiredness
  • sensitivity around the treatment site
  • emotional distress

To help manage these effects, it is important to:

  • get plenty of rest
  • eat healthfully
  • talk to friends and family about any side effects
  • follow instructions, which may involve skin care, from the treatment team
  • avoid spending time in the sun, due to a risk of photosensitivity

Also, monitor for adverse effects and tell the doctor if they occur. The doctor may recommend additional treatments aimed at relieving these.

People may need to speak to their employers about adjusting work schedules or taking medical leave.

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A doctor may recommend radiation therapy to kill cancerous cells.

Radiation therapy can help shrink tumors and kill cancerous cells in the early stages.

This kind of treatment, in combination with other appropriate therapies, can cause cancer to go into remission. In many cases, it does not come back again.

Radiation therapy can also help treat symptoms when cancer has spread widely. At this point, the radiation is part of palliative care, which aims to relieve a person’s symptoms and improve their quality of life. It may also extend a person’s life, in some cases.

Palliative radiation treatment usually involves lower doses and fewer treatment sessions than curative treatment.

In some people with bone cancer, for example, palliative radiation treatment can help stop painful tumors from developing.

Other ways that palliative radiation treatment can help include:

  • relieving pressure or a 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, bleeding, and infections

In people with head and neck cancers, an obstruction in the superior vena cava can affect the return of blood to the heart. Radiation therapy can help relieve this.

Cancer is metastatic when it has spread to other parts of the body. Here, learn about metastatic breast cancer.

Some people feel anxiety and concern about radiation therapy. It has various uses in treating cancer, and it can help achieve complete remission, in some cases.

The National Cancer Institute (NCI) point out that radiation can be costly.

People with health insurance should speak with their provider about coverage. Also, some organizations provide financial support and other help to people who need treatment. The NCI provide a list of options.

Discuss any concerns with the doctor and ask as many questions as possible. Knowing what to expect can help.


Will my hair grow back after radiation therapy?


Radiation therapy only causes hair loss at the site receiving the therapy. Hair loss may be temporary or permanent, depending on the site and the doses. Higher doses of radiation may be more likely to result in permanent hair loss.

Seunggu Han, MD Answers represent the opinions of our medical experts. All content is strictly informational and should not be considered medical advice.