Radiation therapy

Radiation therapy, AKA radiotherapy, is one type of cancer treatment used as part of a treatment plan to control or kill malignant cells. The therapy uses ionizing radiation, gamma rays, delivered by a linear accelerator.

Radiation therapy may be administered by a machine outside the body (external beam radiation therapy) delivered in the form of photon beams, or it may be produced from a radioactive material placed in the body close to the cancer cells (internal radiation therapy) delivered as radioactive isotopes sealed in tiny seeds. These seeds are placed into the patient using a needle or catheter.


The purpose of radiation therapy is to kill cancer cells, ultimately by destroying the abnormal cells DNA. The type of therapy is able to damage the cell’s DNA directly, or by creating charged particles (free radicals) from within the cells, which in turn may damage the DNA.

Malignant cells with damaged DNA will ultimately stop dividing, or simply die. When the damaged cells die, they are broken down by the body and eliminated.


A radiation oncologist will tailor a patient’s treatment plan, beginning with simulation. This process involves detailed imaging scans to show the location of a patient’s tumor. The scans may be composed of CT, MRI, PET (positron emission tomography) or ultrasound.

During such scans, detailed images are created via computer linked to an x-ray machine. For imaging, it is essential that the patient remains in the exact same position. Body molds, head masks and other devices aid in insuring this practice.


Subsequent to the simulation process, the oncologist determines the exact area of treatment, the total radiation dose that will be delivered to the patient and the safest path of radiation delivery, ultimately preserving as much healthy tissue around the tumor as possible.

Radiation therapy is principally used to destroy cancer cells whilst preserving as much healthy tissue as possible.

Learn more about radiation for breast cancer, radiation therapists, and radiation masks.

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