Types of Radiation Therapy
There are two main types of radiation therapy: external beam radiation (teletherapy) and internal radiation therapy (brachytherapy).
External Beam Radiation Therapy (Teletherapy)
External beam radiation therapy is radiation delivered from a distant source, from outside the body and directed at the patient's cancer site. Systems which produce different types of radiation for external beam therapy include orthovoltage x-ray machines, Cobalt-60 machines, linear accelerators, proton beam machines, and neutron beam machines. A radiation oncologist makes decisions regarding the type of system that is best suited to treat a specific cancer patient. External beam therapy is the radiation therapy treatment option used for most cancer patients. It is used to treat many types of tumors including cancers of the head and neck area, breast, lung, colon, and prostate.
Depending upon tumor location, different levels of radiation are used for external beam therapy. Low-energy radiation does not penetrate very deeply into the body and is used mainly to treat surface tumors such as skin cancer. High-energy radiation is used to treat other deeper cancers.
Stereotactic radiation therapy involves focusing the radiation beam on a small area and delivering very high doses. The therapy targets a tumor from many different directions so the beams of radiation converge on the tumor. This way, the ideal amount of radiation needed to destroy tumor cells is delivered directly to the tumor growth, while the amount of exposure to the area surrounding the tumor is minimized. Stereotactic radiation therapy is very effective in treating small tumors such as those in the head and brain.
External beam therapy is painless. Most patients do not need to stay in the hospital while they are having external beam therapy. Patients do not see or feel the actual treatment. Many patients can go home following each treatment, and most patients can even continue with their normal daily activities. Sources of external beam radiation may include, but are not limited to: X-ray, cobalt, linear accelerator, neutron beam, betatron, spray radiation, stereotactic radiosurgery such as gamma knife, and proton beam.
Developed in 1968 by Swedish professors Lars Leksell and Borge Larsson, the gamma knife (sometimes called the "Leksell-Larsson Gamma Knife") is a highly advanced instrument used to treat arteriovenous malformations (AVM), facial pain, benign and malignant brain tumors, and other functional brain disorders. What makes the gamma knife so unique is that it successfully treats these conditions with no incision. Instead, it uses a concentrated radiation dose from Cobalt-60 sources. A total of 201 beams of radiation intersect to form a powerful tool focused on a targeted area of abnormal tissue within the brain. Amazingly, the gamma knife is so precise that it damages and destroys the unhealthy tissue while sparing adjacent normal, healthy tissue.
Internal Radiation Therapy (Brachytherapy)
Brachytherapy involves placing radiation sources as close as possible to the tumor site. Sometimes, they may be inserted directly into the tumor. The radioactive sources or isotopes are in the form of wires, seeds (or molds), or rods. This technique is particularly effective in treating cancers of the cervix, uterus, vagina, rectum, eye, and certain head and neck cancers. It is also occasionally used to treat cancers of the breast, brain, skin, anus, esophagus, lung, bladder, and prostate.
In some instances, brachytherapy may be used in conjunction with external beam therapy. When both forms are employed, the external beam radiation is intended to destroy cancerous cells in a large area surrounding the tumor, while the brachytherapy delivers a boost, or higher dose of radiation, to help destroy the main concentrated mass of tumor cells.
There are several types of brachytherapy characterized by different methods of placing radiation inside the body: interstitial brachytherapy, intracavitary brachytherapy, intraluminal radiation therapy, and radioactively tagged molecules given intravenously.Interstitial brachytherapy involves implanting radioactive needles or wires in the tumor area. The radioactive sources may be put in and taken out on the same day; removed from the body after several days; or may stay in the patient permanently.
With intracavitary brachytherapy, a radiation oncologist places radioactive sources, using a metal or plastic device (applicator), in body cavities such as the vagina, uterus, or larynx to irradiate the walls of the cavity or nearby tissues. Usually the radioactive source is afterloaded into the applicator. When the specified dose of radiation has been delivered to the tumor, the physician removes the applicator containing the radioactive isotope.
Intraluminal radiation therapy delivers radiation to hollow organs. For example, a surgeon or a radiation oncologist inserts a specially designed tube or applicator into the lumen, or opening, of the esophagus to treat cancer.
Finally, radioactive particles can be attached to small molecules and given intravenously. For example, I-131 is used intravenously to treat bony metastases.