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Ionising
and non-ionising radiation
Ionising
radiation at high doses causes cancer in humans: only a few
cancer types have never been related to ionising radiation.
This has been known for decades, and excellent summaries of
the scientific literature are available. The
International Agency for Research on Cancer
(IARC) recently classified X-rays, g-rays and neutrons as
carcinogenic to humans (Group 1). This is irrespective of
the different patterns of energy release and penetrating power
of the different types of ionising radiation. Energy at high
levels may lead to cellular and DNA damage followed by cell
killing, whereas at lower doses it may lead to mutations increasing
the risk of cancer. The International Commission on Radiological
Protection (ICRP) issues recommendations for radiological
protection based on the existing scientific literature.
 High-dose
ionising radiation is used in medicine to treat cancer. These
types of exposures are at present outside the scope of the
European Code Against Cancer. However, much of our evidence
on the effects of ionising radiation on humans is derived
from such uses, and from the atomic bomb survivors at Hiroshima
and Nagasaki. The main source of radiation to the human population
comes from the natural background, both terrestrial and cosmic,
whilst the man-made sources, such as atmospheric nuclear testing,
nuclear accidents (e.g. Chernobyl) and nuclear power production,
which cause the most public concern, cause only very little
exposure (Table 9).
The
United Nations Scientific Committee on the Effects of
Atomic Radiation (UNSCEAR) estimates the population risk of
dying from cancer after an acute dose of 1000 mSv is about
9% for
men and 13% for women. The estimates could be reduced by 50%
for chronic exposures. The worldwide average annual effective
dose is 2.4 mSv. The lifetime exposure of the population to
all
sources of ionising radiation was estimated by the National
Radiological
Protection Board to account for 1% of all fatal cancers in
the
UK.(http://www.nrpb.org/radiationtopics/risks/cancer
risk.htm
–
22 November 2002). Only 1% of this risk is ascribed to the
small
doses from man-made radiation.
For
the purpose of the European Code Against Cancer, this review
concentrates on the possible effects of the natural background
radiation, terrestrial (in the form of radon gas) and cosmic
radiation, as it is possible to control exposure to both.
Furthermore, we assess the cancer risk related to the Chernobyl
accident and that among nuclear workers and people living
near nuclear installations. Diagnostic radiation is of concern
for the population groups undergoing examinations, be it screening
of healthy individuals with mammography or computed tomography
(CT) scans for lung cancer or when there is a suspicion of
thyroid disease. Screening with low-dose CT for lung cancer
is reported to give an effective dose of between 0.2 and 1
mSv. Using the risk factor of 5% per 1 Sv (ICRP 60), this
would imply one to five radiation induced fatal cancers per
100.000 examinations. Mammography screening for breast cancer
typically gives an absorbed average glandular dose of 3 mGy.
It has been estimated in Sweden that among women aged 50–69
years, with a reduction in breast cancer mortality due to
a mammographic screening programme of 25%, that 560 deaths
from breast cancer would be avoided. It is estimated that
the effect of the radiation would be to induce between 1 and
5 fatal breast cancers per 100.000 examinations. Although
the collective dose from diagnostics to the population is
small relative to natural radiation, benefit analyses should
be performed to avoid unnecessary exposure.
Non-ionising
radiation from sources such as power lines, electrical equipment,
mobile phones and solar radiation raise public concern as
to a possible carcinogenic effect. The ICNIRP (International
Commission on Non-ionising Radiation Protection) issues guidelines
for limiting exposure, and the German "Stralenschutzkommission"
and the UK NRPB recently published reviews assessing the health
risks. The evidence on power lines and mobile phones are dealt
with in this section, whereas solar radiation is dealt with
separately.
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