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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.
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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.
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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.
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.
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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.
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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.
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