Radiation Therapies for Cancer Treatments

Radiation therapy uses high-energy X-rays, gamma rays, and charged particles to damage the DNA of cancer cells, stop cell division, and cause cell death. Since radiation therapy will damage normal cells, use of radiation treatments must be carefully planned and controlled to minimize side effects. Planning includes the choice of radiation source, target area(s), and dosages.


Radiation sources include external radiation from a machine outside the body or from a radioactive source inside the body. For internal radiation or brachytherapy, the source consists of a radioactive material placed inside the body near the tumor. External radiation and internal radiation methods allow doctors a wide choice of approaches for safe and effective cancer treatments.


A patient may receive radiation therapy before or after surgery. Radiation treatment before surgery serves to shrink tumors. Radiation treatment after surgery serves to destroy any remaining cancerous cells and prevent recurrences. When surgery is not an option, patients receive radiation therapy alone or in combination with chemotherapy.

The total dose of radiation that normal tissues can receive without causing serious damage is well documented. This knowledge is of great value to the radiation oncologist when planning treatment. For example, radiation therapy to pelvis region cancers must be carefully controlled because of the presence of reproductive organs.

Planning radiation therapy requires a thorough knowledge of the location and size of the tumor. Detailed imaging scans are obtained before any treatment plan is formulated. These imaging scans include computed tomography (CT), magnetic resonance imaging (MRI), positron emission tomography (PET), and ultrasounds. The radiation oncologist's first decision will be the radiation source.

External Radiation Therapy

External beam radiation therapy consists of a stream of X-ray or gamma-ray photons. A common treatment is termed 3-dimensional conformal radiation therapy (3D-CRT). Computer software controls specially designed 3D-CRT machines to scan precisely shaped areas containing the tumor and a small fraction of surrounding normal tissue.

A newer treatment is termed intensity-modulated radiation therapy (IMRT) that employs hundreds of small collimators to shape and modulate the radiation beam. IMRT is used to deliver different doses of radiation to different areas of a tumor and nearby tissues in a single dose. A form of IMRT called Tomotherapy has shown promise for radiation therapy to the pelvis region and use as part of uterine cancer treatments.

Internal Radiation Therapy - Brachytherapy

Brachytherapy uses radiation from radioactive materials delivered to a tumor. Several therapy techniques are used. Interstitial therapy surgically places the source in the tumor tissue. Alternatively, radioactive isotopes are periodically delivered as small pellets through needles or catheters. Another therapy chemically directs radioactive material to a tumor with tumor antibodies. This technique has been tested in uterine cancer treatments.