Bma Illustrated Medical Dictionary

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.
radiopaqueThis term describes any-
thing that blocks radiation, especially
X-raysand 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.
radiotherapyTreatment of cancerand,
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 carcinomaand 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.

radiumA rare, radioactive, metallic ele-

ment that occurs naturally only as

compounds in uraniumores.

RADIOPAQUE

R

RADIOTHERAPY

Linear accelerator

(radiation source)

Control panel

Beam of radiation

Adjustable table

RADIUM

EXTERNAL BEAM RADIOTHERAPY