world cancer report - iarc

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