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Types of Radiation Therapy

Radiation therapy uses high-energy radiation to shrink tumors and kill cancer cells. X-rays, gamma rays, and charged particles are types of radiation used for cancer treatment. About half of all cancer patients receive some type of radiation therapy sometime during the course of their treatment.

Radiation therapy kills cancer cells by damaging their DNA (the molecules inside cells that carry genetic information and pass it from one generation to the next).  Radiation therapy can also damage normal cells, leading to side effects. Doctors take potential damage to normal cells into account when planning a course of radiation therapy. The amount of radiation that normal tissue can safely receive is known for all parts of the body. Doctors use this information to help them decide where to aim radiation during treatment.

The radiation may be delivered by a machine outside the body (external-beam radiation therapy), or it may come from radioactive material placed in the body near cancer cells (internal radiation therapy, also called brachytherapy).

External Beam Radiation Therapy

Patients usually receive external-beam radiation therapy in daily treatment sessions (10-15 minutes each) over the course of several weeks. The number of treatment sessions depends on many factors, including the total radiation dose that will be given. There are a few different techniques that may be used in the delivery of external-beam radiation therapy:

  1. One of the most common types of external-beam radiation therapy is called 3-dimensional conformal radiation therapy (3D-CRT). 3D-CRT uses very sophisticated computer software and advanced treatment machines to deliver radiation to very precisely shaped target areas.
  2. Some patients benefit from a more highly focused external beam therapy called Intensity Modulated Radiation Therapy (IMRT).  The goal of IMRT is to increase the radiation dose to the areas that need it and reduce radiation exposure to specific sensitive areas of surrounding normal tissue.  Your Radiation Oncologist will determine if IMRT is appropriate for you.
  3. Image-guided radiation therapy (IGRT). In IGRT, X-ray images are taken immediately before each daily treatment is delivered. These images are used by the therapists (the staff that actually delivers your treatment each day) to adjust your position so you receive precisely the treatment your doctor has ordered.


Internal radiation therapy (brachytherapy) is radiation delivered from radiation sources (radioactive materials) placed inside or on the body. Permanent interstitial brachytherapy uses radiation sources about the thickness of a pencil lead placed within tumor tissue, such as within a prostate tumor.  The sources are surgically sealed within the body and left there, even after all of the radiation has been given off. The remaining material (in which the radioactive isotopes were sealed) does not cause any discomfort or harm to the patient.



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