world cancer report - iarc
world cancer report - iarc
world cancer report - iarc
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RADIATION<br />
SUMMARY<br />
> Exposure to ionizing radiation from natural<br />
as well as from industrial, medical<br />
and other sources, can cause a variety<br />
of neoplasms, including leukaemia,<br />
breast <strong>cancer</strong> and thyroid <strong>cancer</strong>.<br />
> Sunlight is by far the most significant<br />
source of ultraviolet irradiation and<br />
causes several types of skin <strong>cancer</strong>, particularly<br />
in highly-exposed populations<br />
with fair skin, e.g. Australians of<br />
Caucasian origin.<br />
> Extremely low frequency electromagnetic<br />
fields generated by electrical<br />
power transmission have been associated<br />
with an increased risk of childhood<br />
leukaemia, but the findings are not conclusive.<br />
Natural and man-made sources generate<br />
radiant energy in the form of electromagnetic<br />
waves. Their interaction with biological<br />
systems is principally understood at<br />
the cellular level. Electromagnetic waves<br />
are characterized by their wavelength, frequency,<br />
or energy. Effects on biological<br />
systems are determined by the intensity of<br />
the radiation, the energy in each photon<br />
and the amount of energy absorbed by the<br />
exposed tissue.<br />
The electromagnetic spectrum extends<br />
from waves at low frequency (low energy),<br />
referred to as “electric and magnetic<br />
fields”, to those at very high frequencies,<br />
which are often called “electromagnetic<br />
radiation” (Fig. 2.38). The highest-energy<br />
electromagnetic radiation is X- and γ-radiation,<br />
which have sufficient photon energy<br />
to produce ionization (i.e. create positive<br />
and negative electrically-charged atoms<br />
or parts of molecules) and thereby break<br />
chemical bonds. Other forms of ionizing<br />
radiation are the sub-atomic particles<br />
(neutrons, electrons (β-particles) and α−<br />
particles) that make up cosmic rays and<br />
are also emitted by radioactive atoms.<br />
Non-ionizing radiation is a general term for<br />
that part of the electromagnetic spectrum<br />
which has photon energies too weak to<br />
break chemical bonds, and includes ultraviolet<br />
radiation, visible light, infrared radiation,<br />
radiofrequency and microwave<br />
fields, extremely low frequency (ELF)<br />
fields, as well as static electric and magnetic<br />
fields.<br />
Ionizing radiation<br />
Exposure to ionizing radiation is unavoidable<br />
[1]. Humans are exposed both to Xrays<br />
and γ−rays from natural sources<br />
(including cosmic radiation and radioactivity<br />
present in rocks and soil) and, typically<br />
to a much lower extent, from man-made<br />
sources (Fig. 2.35). On average, for a member<br />
of the general public, the greatest contribution<br />
comes from medical X-rays and<br />
the use of radiopharmaceuticals, with<br />
lower doses from fallout from weapons<br />
testing, nuclear accidents (such as<br />
Chernobyl), and accidental and routine<br />
releases from nuclear installations. Medical<br />
exposures occur both in the diagnosis (e.g.<br />
radiography) of diseases and injuries and in<br />
the treatment (e.g. radiotherapy) of <strong>cancer</strong><br />
and of some benign diseases. Occupational<br />
exposure to ionizing radiation occurs in a<br />
number of jobs, including the nuclear<br />
industry and medicine. Airline pilots and<br />
crew are exposed to cosmic radiation.<br />
Cancer causation<br />
Ionizing radiation is one of the most<br />
intensely studied carcinogens [2-4].<br />
Fig. 2.34 Modern diagnostic radiology is no longer<br />
a significant source of exposure to ionizing radiation.<br />
Fig. 2.35 Estimated annual dose of ionizing radiation received by a member of the general public.<br />
Radiation 51