of their cancer. In external beam radiation ther-
apy, the source of radiation is outside the body,
directed toward the tumor using a machine. The
radiation oncologist determines the precise point
at which the radiation needs to enter the body,
called the treatment portal, and places small tattoo
dots to mark its boundaries. These tattoos are per-
manent and serve as the template for aligning the
radiation delivery path.
The machine that delivers the radiation therapy
is either a linear accelerator (which is most com-
mon) or a cobalt machine. These are similar in
appearance to a large X-RAY machine. When
receiving radiation therapy the person lies on a
table beneath the machine, often positioned with
supports and blocks to maintain the proper align-
ment for the radiation to hit the tumor. Each
treatment session may take 15 to 30 minutes,
though the actual delivery of radiation takes only
a few minutes.
Radiation therapy does not hurt or cause any
discomfort, though the experience can be some-
what stressful for people who are claustrophobic
(become uncomfortable in closed spaces) because
the machine is very large and often very close
during treatment. Because the source of the radia-
tion is outside the body, the person receives only
the directed energy and does not become radioac-
tive. External radiation therapy is often among the
treatments for LUNG CANCER, BREAST CANCER,
PROSTATE CANCER, COLORECTAL CANCER, Hodgkin’s
lymphoma, THYROID CANCER, pharyngeal cancer,
and some types of brain cancer.
INTRAOPERATIVE RADIATION THERAPY
Another form of external beam radiation therapy
is intraoperative radiation, in which the person
receives radiation to the surgical bed (site where
the surgeon removed the tumor). Intraoperative
radiation takes advantage of direct exposure to
the site of the cancer to destroy any cancer cells
that may have penetrated the tissue surrounding
the tumor.Internal radiation therapy, also called radiation
seeding or brachytherapy, more directly targets
the tumor with radioactive pellets (radioisotopes
encased in thin wire containers) about the size of
grains of rice, implanted in the body into or very
near the tumor. Internal radiation therapy delivers
a higher dose of radiation more directly to the
tumor site, and often for a shorter duration, than
would be possible with external beam radiation
therapy. Internal radiation may be among the
treatments for breast cancer, ENDOMETRIAL CANCER,
thyroid cancer, CERVICAL CANCER, prostate cancer,
and some cancers of the head and neck.
Internal radiation therapy may be- interstitial, in which the radiation oncologist
implants the radioactive pellets into the tumor
or the tissue surrounding the tumor - intracavitary, in which the radiation oncologist
inserts the radioactive pellets into a natural
body cavity such as the UTERUSor RECTUM - intraluminal, in which the radiation oncologist
inserts the radioactive pellets into a natural
body passage such as the ESOPHAGUSor VAGINA
The implantation generally takes place with the
person under general, regional, or local
ANESTHESIA. After implantation the person is
radioactive—that is, he or she emits ionizing radi-
ation that can expose other people to its effects.
Sometimes it is necessary to restrict contact with
other people until the end of the course of treat-
ment when the radioisotope dissipates enough to
emit a level of ionizing radiation that is within
safe limits. Sometimes the surgeon implants the
pellets after an OPERATIONto remove the tumor. An
internal radiation implant remains in place for a
few days to several weeks in most circumstances,
though may remain for a few minutes to a few
hours when the dose of radiation is very high and
indefinitely when the optimal therapy is low-dose
radiation over an extended time.Risks, Side Effects, and
Complications of Radiation Therapy
About half of people who have cancer receive
radiation therapy during the course of their treat-
ment. The general short-term side effects of radia-
tion therapy include- damage to the skin in the treatment area, simi-
lar to SUNBURN - damage to hair follicles in the treatment area,
resulting in local thinning or loss of hair
radiation therapy 389