EXTERNAL BEAM RADIOTHERAPY
images can also
be made using a
computer to record
a series of images.
some disorders at
than other imag-
in the functioning
of an organ often
occur before the
organ is affected.
The technique is
also used to de-
tect disorders that
function of organs.
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
hours. The radionuclides carry virtually
no risk of toxicity or hypersensitivity.
radiopaque This term describes any-
thing that blocks radiation, especially
and gamma rays. As many body
some X-ray imag-
ing procedures require the introduction
of radiopaque substances into the body
to make organs stand out clearly.
radiotherapy Treatment of
occasionally, some noncancerous tu-
or other radiation.
Radioactive sources produce ionizing
, 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
. 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
be destroyed using radioactive iodine.
Radiotherapy is usually performed on
an outpatient basis.
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
) or into a body cavity (see
). 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
Beam of radiation