Radiation Therapy to Treat Cancer

Radiation therapy (also called radiotherapy) is a cancer treatment that uses high doses of radiation to kill cancer cells and shrink tumors. At low doses, radiation is used in x-rays to see inside your body, as with x-rays of your teeth or broken bones. At high doses, radiation therapy kills cancer cells or slows their growth by damaging their DNA. Cancer cells whose DNA is damaged beyond repair stop dividing or die. When the damaged cells die, they are broken down and removed by the body. Radiation therapy does not kill cancer cells right away. It takes days or weeks of treatment before DNA is damaged enough for cancer cells to die. Then, cancer cells keep dying for weeks or months after radiation therapy ends. 

Types of Radiation Therapy

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.

Side Effects

Radiation therapy is a local treatment. This means that it only affects the area of the body where the tumor is located. For example, people do not usually lose their hair from having radiation therapy. But radiation therapy to the scalp may cause hair loss.

Common side effects of radiation therapy include:

Skin Problems * Fatigue *

Some side effects depend on the type and location of radiation therapy.

Head and neck. Radiation therapy aimed at a person’s head or neck may cause these side effects

Dry mouth * Mouth and gum sores * Difficulty Swallowing * Stiffness in the Jaw * Nausea * Hair Loss * Tooth Decay *

Chest. Radiation therapy aimed at the chest may cause these side effects:

Difficulty Swallowing * Shortness of breath * Breast or nipple soreness * Shoulder stiffness * Cough * fever * fullness of the chest * Radiation fibrosis

Stomach and abdomen. Radiation therapy aimed at the stomach or abdomen may cause these side effects:

Nausea and vomiting * Diarrhea * Perforation

Pelvis. Radiation therapy aimed at the pelvis may cause these side effects:

Diarrhea * Rectal Bleeding * Incontinence * Bladder irritation

Potential side effects for men include: Sexual problems * Lowered sperm counts and reduced sperm activity

For women: Changes in menstruation * Symptoms of menopause * Infertility

Workind During Radiation Therapy

Some people are able to work full-time during radiation therapy. Others can work only part-time or not at all. How much you are able to work depends on how you feel. Ask your doctor what you may expect from the treatment you will have. You are likely to feel well enough to work when you first start your radiation treatments. As time goes on, do not be surprised if you are more tired, have less energy, or feel weak. Once you have finished treatment, it may take just a few weeks for you to feel better—or it could take months.

Special Dietary Needs

Radiation can cause side effects that make it hard to eat, such as nausea, mouth sores, and throat problems called esophagitis. Since your body uses a lot of energy to heal during radiation therapy, it is important that you eat enough calories and protein to maintain your weight during treatment. If you are having trouble eating and maintaining your weight, talk to your doctor. You might also find it helpful to speak with a dietitian.

Lifetime Dose Limits

There is a limit to the amount of radiation an area of your body can safely receive over the course of your lifetime. Depending on how much radiation an area has already been treated with, you may not be able to have radiation therapy to that area a second time. But, if one area of the body has already received the safe lifetime dose of radiation, another area might still be treated if the distance between the two areas is large enough.


If you’re receiving radiation to a tumor, your doctor may have you undergo periodic scans after your treatment to see how your cancer has responded to radiation therapy.

In some cases, your cancer may respond to treatment right away. In other cases, it may take weeks or months for your cancer to respond. Some people aren’t helped by radiation therapy.