What is radiation therapy?

Radiation therapy is a form of cancer treatment that uses radiation (strong beams of energy) to kill cancer cells or keep them from growing and dividing. Radiation therapy may be used in conjunction with surgery or chemotherapy to treat cancer.

Doctors who specialize in radiation therapy — who are called radiation oncologists— determine the optimum doses for specific types of cancer that maximize effectiveness and minimize any harm to healthy tissues. The radiation oncologist knows what type of therapy is best suited for you and your specific type of cancer.

What are the types of radiation therapy?

External radiation therapy

External beam radiation therapy (EBRT) is the most common form of radiation therapy. Beams of high-energy radiation are directed at the tumor. The position of the machine can be changed to aim the beams at different angles.

External radiation therapy is usually given five days a week for one to eight weeks, depending on the cancer. On occasion, a single treatment may be recommended. The daily treatment usually takes only a few minutes.

Types of external radiotherapy include:

  • 3D conformal radiation therapy: Computed tomography (CT) scans and special computer software help create a three-dimensional computer model of the area to be treated. Treatments are more precisely targeted to the tumor, sparing surrounding normal tissue.
  • Intensity-modulated radiation therapy (IMRT)/volumetric modulated arc therapy (VMAT): Intensity modulated radiotherapy provides even more precise radiation therapy. This multi-beam system varies dose intensity and narrows in on diseased cells. VMAT does this over an arc, which tends to be faster.
  • Image guided radiotherapy (IGRT): Sometimes three dimensional imaging done before treatment can help ensure the best alignment to the target. This is usually done by getting a CT scan prior to each treatment. Other imaging options include X-rays, ultrasound, systems that track internal seeds and cameras that track a surface as it moves.
  • Stereotactic radiosurgery/Gamma Knife radiosurgery: The Gamma Knife is considered the "gold standard" for radiation treatment for brain tumors or lesions. The Gamma Knife provides results comparable to or better than conventional surgery in many cases, without the need for a surgical incision or long recovery in the hospital. Radiosurgery is usually a single treatment, although in some cases you may have treatment broken up into a few treatments over separate days.
  • Stereotactic body radiation therapy (SBRT): This type of treatment focuses high doses of intense radiation to targets outside the head. This type of treatment is usually given in one to five treatments. Sometimes special systems that control or track your breathing are necessary to further minimize radiation to the healthy parts of your body.
  • Intraoperative radiation: Intraoperative radiation therapy (IORT) allows for radiation to be delivered at the time of surgery, which may help avoid the need for external radiation later. The radiation is better focused to areas that have some tumor left behind.

Internal radiation therapy

Brachytherapy and radiopharmaceuticals

In some cases internal radiation therapy is as effective in treating cancer as external. Brachytherapy involves implanting a radioactive source, or "seed," in or around a tumor. The source emits a high dose of radiation to a small area to kill cancer cells. Implants can be temporary or permanent.

  • Examples of temporary brachytherapy implants include gynecologic, esophageal, orbital (eye) and coronary artery implants.
  • An example of permanent brachytherapy implant is a low-dose rate prostate seed implant.

Radiopharmaceuticals are another way of delivering radiotherapy, in the form of a radioisotope bound to a carrier. Examples of radio pharmaceuticals include TheraSphere™, used to treat certain liver tumors, and Zevalin®, used to treat certain lymphomas.

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