Radiation can be delivered by two different methods: external beam radiation therapy and internal radiation therapy (brachytherapy). In the former, the radiation is delivered from a machine outside the body, while the latter involves inserting the source of radiation directly into the body.

Some patients have a combination of radiation therapies that take place either consecutively or concurrently. Several factors will determine the type of radiation delivery to be used, including:

• Cancer type, stage and location
• How far the radiation needs to penetrate
• Known effectiveness of radiation for the cancer type
• Patient’s general health and medical history
• Other types of cancer treatments for the patient

External beam radiation therapy

This type of radiation is a non-invasive, non-surgical treatment that delivers high energy x-rays or lower energy electrons. It is performed on an outpatient basis, usually five days a week for five to seven weeks. Delivery of external beam radiation is essentially painless and can be delivered in relatively short sessions. It can be used to treat most types of cancers including cancer of the:

• Bladder
• Brain
• Breast
• Cervix
• Head and neck
• Lung
• Prostate
• Vagina

External beam radiation therapy is used primarily to destroy cancer cells in a specific area. It also may be used to relieve pain or other problems associated with cancer that has spread from the primary site to other parts of the body.

External beam radiation therapy varies according to the photon energy produced by the machines, the type of beams that are produced (electrons, x-rays or gamma rays), when the treatment is given and the number of beams used in the procedure.

Other uses of external beam radiation therapy include:

• Intraoperative radiation therapy (IORT). Used to treat localized cancers that cannot be completely removed or those that are at great risk of recurring in nearby tissues. This form of radiation is given in a single, high-intensity dose immediately following surgery to remove a cancer, while the surgical wound is still open. Special shields are used to protect nearby tissues before the radiation is directed at the tumor site. IORT therapy will likely require a hospital stay. It may be used to treat:
  
  
• • Thyroid cancer
  • Colorectal cancer
  • Gynecologic cancers
  • Small intestinal cancer
  • Pancreatic cancer

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    IORT is also being tested in clinical trials on brain tumors and pelvic sarcomas.

   

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  • Prophylactic cranial irradiation (PCI). Radiation directed at the brain when a primary cancer is known to have a high risk of spreading to the brain.

  The energy used in external beam radiation therapy comes from any of the following sources:

  • X-rays. A type of photon (packet of energy) that is widely used in medicine for both diagnosis and treatment. Machines called linear accelerators are used to generate x-rays, with lower-energy beams to destroy cancer cells on the body’s surface and higher-energy beams to kill cancer cells deeper in tissues and organs.
    
    
  • Gamma rays. Gamma rays are produced when certain isotopes (one of two or more atoms that have the same number of protons but different numbers of neutrons in their nuclei) break down and release radiation energy. Individual elements break down at different rates and give off varying amounts of energy. The amount of energy determines how deeply the radiation penetrates the body.
    
    
  • Particle beams. Particle beams consist of fast-moving subatomic particles and are created by linear accelerators, synchrotrons and cyclotrons that produce and accelerate particles. In particle beam therapy, the beam is produced by a variety of methods. Some particle beams penetrate less deeply into tissue than x-rays and gamma rays. As a result, they are often used to treat cancers on the skin surface or just below the skin.
    
    Proton beam therapy is a type of particle beam radiation in which protons are deposited over a small area known as the Bragg peak. This allows physicians to deliver high-dose treatments to the tumor while minimizing damage to the healthy tissue in front of and behind the tumor. This form of therapy is not commonly available in the United States and is reserved for cancers that are difficult or dangerous to treat with surgery. In some cases, it is combined with other forms of radiation.

  Internal radiation therapy (brachytherapy)

  The radiation in this form of therapy is inserted directly into or next to the tumor. The source of the radiation can be injected (housed in special applicators) or implanted. These radiation implants are very small and produce little discomfort. They include:

  • Thin wires
  • Catheters
  • Ribbons
  • Capsules
  • Seeds

  Brachytherapy has the advantage of allowing a high dose of radiation to be delivered to a small area. This can be especially useful if the tumor requires high doses of radiation that would be likely to damage normal tissues if a more widespread treatment method, such as external radiation, was used. The source of radiation implanted in brachytherapy can be either permanent or temporary. Permanent pellets eventually use up all the radioactive material and are harmless when left in the body.

  Brachytherapy is delivered in the following ways:

  • Interstitial radiation therapy. Inserted into tissue at or near the tumor site, it is sometimes used as an additional dose of radiation after women have received external radiation to treat breast cancer. It also is used to treat cancers of the:
    
    
  • • Head and neck
    • Prostate
    • Cervix
    • Ovary
    • Perianal and pelvic regions
      
      
  • Intracavitary (intraluminal) radiation therapy. Inserted into the body with an applicator to treat uterine cancer. Researchers are also testing the effectiveness of using intracavitary radiation therapy to treat cancers of the:
    
    
  • • Breast
    • Trachea and bronchia
    • Esophagus
    • Gallbladder
    • Head and neck
    • Cervix and vagina
    • Rectum
      
      
  • Systemic radiation therapy. Radioactive materials such as iodine 131 or strontium 89 are injected or given by mouth and will concentrate in certain tissues. Systemic radiation therapy is used to treat cancer of the thyroid and adult non-Hodgkin’s lymphoma.
    
    

  Patients who receive brachytherapy may be treated as outpatients or may be required to stay in the hospital for a period of time.