What is radiation therapy?

Radiation therapy, also known as radiotherapy, is a common treatment for cancer where radiation is used to destroy or shrink a tumor. It is often combined with other therapies, such as chemotherapy, surgery, targeted therapy or hormone therapy.

During radiation therapy, high-energy radiation from X-rays, gamma rays, protons or electron beams is used to precisely target tumors. The radiation damages the DNA inside cancer cells, causing them to stop dividing and die. The goal of radiation therapy is to treat a specific part of the body to reduce damage to normal cells.

More than half of people in the United States diagnosed with cancer will have some form of radiation therapy.

female patient receiving radiation therapy

Types of radiation therapy

Your doctor might recommend different types of radiation therapy depending on your cancer diagnosis, what stage it is and your overall health. Radiation therapy can be external, where a machine outside your body targets the tumor with high-energy rays, or internal, where a radioactive source is put inside your body.

External beam radiation therapy (EBRT)

During EBRT, a machine aims radiation at a specific part of your body to target the tumor. Most machines use photon beams, which can target tumors deep inside your body. Proton beams, which are made up of electrons (particles with a positive charge), can also be used.

A computer analyzes images of your body to calculate the precise dose and treatment path for the radiation, minimizing damage to nearby healthy cells. There are several different types of external beam radiation therapy:

  • 3D conformal radiation therapy: MRI and CT images allow doctors to design radiation beams that conform to the size and shape of the tumor. Beams are delivered from many directions, allowing the machine to use high doses of radiation without harming nearby healthy tissue.
  • Intensity-modulated radiation therapy (IMRT): IMRT is a type of 3D conformal radiation therapy that uses smaller beams of radiation. Their strength can be varied to give higher doses to parts of the tumor.
  • Image-guided radiation therapy (IGRT): This is a type of IMRT where images are taken during treatment to detect changes in the tumor’s size and location. The radiation dose can be adjusted to improve accuracy.
  • Stereotactic radiosurgery: This is often used to treat small tumors in your brain or spinal cord when surgery is not an option. Small beams aimed at the tumor from different directions deliver a precisely targeted dose of radiation to the tumor with less damage to nearby areas. 
  • Stereotactic body radiation therapy (SBRT): Similar to stereotactic radiosurgery, radiation beams are used to target small tumors outside the brain, such as those in the liver and lungs.

How to prepare for radiation therapy

Your care team, including your radiation oncologist (a cancer doctor who specializes in radiation therapy) and other healthcare professionals, will plan your treatment. Your doctor will explain what to expect from treatment, your treatment schedule and possible side effects. You will have a chance to ask questions and raise any concerns.

Your doctor will tell you if you need to do anything, such as stop taking other medicines or follow a special diet. You might also need to talk to your employer about taking time off and ask a family member or friend to drive you to appointments.

It is normal to feel anxious and overwhelmed following a cancer diagnosis. Your nurse navigator can connect you with cancer support services that may help you manage the emotional and physical aspects of your care.

What to expect

Your radiation treatment will take place at an outpatient center or hospital. Before your first appointment, you will have a planning appointment with your care team. You will have a physical exam and, in some cases, imaging tests. 

On the day of the appointment, you should arrive on time and wear comfortable, loose-fitting clothes that are easy to take off if required. Follow any instructions from your doctor about what to eat. If you are having internal radiation therapy, you may need to prepare to stay overnight in the hospital.

Before treatment

Your doctor will examine you, review your medical history and test results, and identify the area to treat.

If you are having external beam radiation therapy, you will be asked to take part in a simulation. A radiation therapist will use imaging scans to identify the exact places on your body where the beams will be aimed. They might use a mold or mask to make sure you are in the same position for treatment and mark the treatment areas using semi-permanent ink. Your care team will calculate the exact dose of radiation required.

Radiation therapy side effects

Radiation can damage healthy cells as well as cancer cells, leading to side effects. These can depend on the type of cancer, treatment and radiation dose. Some people experience many side effects, while others are not affected.

Common side effects are fatigue and changes to your skin after treatment. You might also experience: 

  • Changes in taste
  • Diarrhea
  • Hair loss
  • Headache
  • Fertility problems
  • Mouth problems
  • Nausea and vomiting
  • Sexual problems
  • Skin changes
  • Swelling
  • Throat problems, such as difficulty swallowing
  • Thyroid issues
  • Urinary and bladder problems

Long-term side effects

Most side effects go away a few months after treatment, but some people have late side effects, which are side effects that develop months or years after treatment. Late side effects of radiation therapy include joint problems, mouth problems and infertility. Although rare, radiation therapy can increase your chances of getting another type of cancer later in life.

Talk to your doctor or nurse before or after treatment about side effects and how you can manage them. If you are concerned about your ability to have children in the future, your doctor can recommend fertility preservation options before treatment.

Frequently asked questions

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