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Radiation therapy is the use of high-energy rays to attack cancer. The intent
of using radiation therapy is to damage or destroy the genetic material of
cancer cells, rendering them unable to grow and thus spread.
During treatment, radiation is aimed only at the area to be treated, but because it
must often go through skin and other organs to reach a tumor, the body’s
healthy cells become damaged, too. The body, however, is able to repair these
damaged cells and restore them to their proper function.
Aside from its use as a single treatment, radiation therapy has been shown to
enhance the effects of chemotherapy. It is also often used in combination with
chemotherapy to shrink a tumor before its surgical removal. For tumors that are
inoperable, radiation can be effective in reducing or alleviating the pain,
bleeding, or intestinal blockage associated with these tumors.
The most common form of radiation therapy used for colorectal cancer is
called external beam radiation therapy. During this procedure, the
patient is positioned so that a beam from a machine positioned outside the body may be
aimed at the tumor. The radiation treatment itself lasts only a few minutes and
is generally given five times a week for several weeks. One of the primary uses
of this form of therapy is to attack tumors that are attached to an internal
organ, or to kill any unseen cancer cells or cancer cells that may remain after
surgery.
A variation of external beam radiation therapy is called endocavitary
therapy. Here too, an external machine is used, but instead of the beam passing
through the body, a device is inserted in the anus, and thus able to treat
rectal tumors directly. This procedure is given in the same increments as
external beam radiation.
Brachytherapy is another form of radiation rarely used with colorectal
cancer. Also called internal radiation therapy, brachytherapy is implemented by
placing small radioactive pellets inside the body and directly into the cancer.
This therapy is generally only used for tumors that cannot be removed through
surgery.
A newer radiation technique for treating colorectal cancer is called
intraoperative radiation therapy, or IORT. This form of therapy is used for
patients with extensive local spreading of rectal cancer. It is administered
while still in the operating room after the surgeon has removed the tumor.
Radiation is then delivered directly to a specific area on the pelvis. Since it
is done during the surgical procedure and offers direct access to the cancer,
higher-than-normal doses of radiation can be given.
Some of the temporary side effects of radiation therapy include mild skin
irritation, bladder and rectal irritation, nausea, diarrhea, and fatigue.
Occasionally rectal and bladder irritation can become a permanent side effect,
but your doctor can recommend methods and treatments that can reduce these
discomforts.
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