RADIOPAQUE
RADIUM
EXTERNAL BEAM RADIOTHERAPY
images can also
be made using a
computer to record
a series of images.
Radionuclide scan-
ning can
detect
some disorders at
an
earlier stage
than other imag-
ing
techniques
because changes
in the functioning
of an organ often
occur before the
structure
of the
organ is affected.
The technique is
also used to de-
tect disorders that
affect
only
the
function of organs.
Moving
images
can provide infor-
mation on blood
flow, the movement of the heart walls,
the flow of urine through the kidneys,
and bile flow through the liver.
Radionuclide scanning is a safe pro-
cedure, requiring only minute doses of
radiation
that
are
excreted
within
hours. The radionuclides carry virtually
no risk of toxicity or hypersensitivity.
radiopaque This term describes any-
thing that blocks radiation, especially
X-rays
and gamma rays. As many body
tissues are
radiolucent,
some X-ray imag-
ing procedures require the introduction
of radiopaque substances into the body
to make organs stand out clearly.
radiotherapy Treatment of
cancer
and,
occasionally, some noncancerous tu-
mours, by
X-rays
or other radiation.
Radioactive sources produce ionizing
radiation
, which destroys or slows down
the development of abnormal cells.
Normal cells suffer little or no long-
term damage, but short-term damage is
a side effect.
Radiotherapy may be used on its own
in an attempt to destroy all the abnormal
cells in various types of cancer, such as
squamous cell carcinoma
and
Hodgkin's
disease
. It may also be used with other
cancer treatments. Surgical excision of
a cancerous tumour is often followed by
radiotherapy to destroy any remaining
tumour cells. Radiotherapy may also be
used to relieve the symptoms of a can-
cer that is too advanced to be cured.
If benefits outweigh risks, radiotherapy
may be used to treat noncancerous dis-
eases; for example, part of an overactive
thyroid gland (see
thyrotoxicosis
) may
be destroyed using radioactive iodine.
Radiotherapy is usually performed on
an outpatient basis.
X-rays
(or some-
times electrons) produced by a machine
called a linear accelerator are aimed at
the tumour from many directions. This
produces a large enough dose of radia-
tion to destroy the tumour. Alternatively,
a source of radiation, in the form of tiny
pellets, is inserted into the tumour
through a hollow needle (see
interstitial
radiotherapy
) or into a body cavity (see
intracavitary therapy
). Radioactive iodine
used to treat thyrotoxicosis is given in
liquid form and drunk through a straw.
There may be unpleasant side effects,
including fatigue, nausea and vomiting,
and loss of hair from irradiated areas.
Rarely, there may be reddening and
blistering of the skin.
radium A rare, radioactive, metallic ele-
ment that occurs naturally only as
compounds in
uranium
ores.
RADIOTHERAPY
Linear accelerator
(radiation source)
Adjustable table
Beam of radiation
R
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