About Radiation Therapy

Radiation therapy uses controlled high-energy rays to treat tumors and other diseases of the body. Radiation works by damaging the DNA inside cells, making them unable to divide and reproduce. Abnormal cancer cells are more sensitive to radiation because they divide more quickly than normal cells.

Over time, the abnormal cells die and the tumor shrinks. Normal cells can also be damaged by radiation, but they can repair themselves more effectively, as when your skin heals itself after sunburn (a mild form of radiation exposure).

The goal of radiation therapy is to maximize the dose to abnormal cells while minimizing exposure to normal cells. The effects of radiation are not immediate; the treatment benefit occurs over time. Typically, more aggressive tumors, whose cells divide rapidly, respond more quickly to radiation. Radiation therapy is painless and will not make you radioactive.

Radiation is often given with the intent of destroying the tumor and curing the disease (curative treatment). However, not all disease or cancer can be cured with radiation. Sometimes radiation is used to relieve symptoms, such as pain or seizures (palliative treatment). Sometimes it is used to prevent tumors from developing or spreading (prophylactic treatment).

There are two ways to deliver radiation:

  • External beam radiation is delivered from outside the body by using a machine to aim high-energy rays (X-rays, gamma rays or photons) at the tumor. Learn more about External Beam Radiation Therapy.
  • Internal radiation (brachytherapy) is delivered from inside the body by surgically placing radioactive material, sealed in catheters or seeds, directly into the tumor. Learn more about Internal Radiation Therapy.


Radiation may be used alone or in combination with other treatments such as surgery, chemotherapy or immunotherapy. If used before surgery, radiation will shrink the tumor to make it easier to remove. If used after surgery, radiation will destroy tumor cells that may have been left behind.

More Information

Need more information about patient care?

Contact UC Health University of Cincinnati Physicians at (513) 475-8400 or visit uchealth.com.

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