Re: Diagnostic Radiation Exposure, Renewed Concerns
- From: "D. Spencer Hines" <panther@xxxxxxxxxxxxx>
- Date: Sat, 17 May 2008 23:12:33 +0100
Very Useful...
Thanks For Posting It.
DSH
"Bolaleman" <hulle06@xxxxxxxxxxx> wrote in message
news:eb0a88c2-a342-4356-afe2-6312ec8c3c8b@xxxxxxxxxxxxxxxxxxxxxxxxxxxxxxx
According to recently published studies, up to 2 percent of cancers
could be related to the administration of diagnostic x-rays. There is
a need to establish the benefit/risk balance for any of the commonly
suggested CT screening techniques.
Various recently published studies about the relationship between low
dose radiation and cancer fanned again the discussion about risk and
benefits of modern diagnostic techniques and in particular Computer
Tomography (CT). According to an article recently published in IMAGE
(Marie H. Meynadier, Vol. 21, no. 10 - March 10, 2008), it is
predictable that in a few decades up to 2 percent of cancers in the
United States could be linked to the administration of diagnostic x-
rays, even if the ability to monitor the increase in cancer related to
radiation exposure will be very difficult as radiation-induced cancer
can take up to 20 years to develop.
Since many years the relationship between cancer development and
radiation exposure has been studied and there are hundreds if not
thousands of publications related to this topic. The problem is that a
third of all people get cancer anyway, at some time in their lives,
and hence it is quite difficult to find evidence that low doses of
radiation cause cancers that would not have otherwise occurred. Even
for the 80,000 to 90,000 survivors of the atomic bombs exploded over
Hiroshima and Nagasaki, exposed to very large radiation doses, it has
been hard to find a direct relationship between excess cancer
development and radiation exposure. According to Japanese statistics,
from the people who were exposed in 1945 (and did not die immediately)
nearly half are still alive. A statistically significant increase in
cancer was found at relatively high exposure level of 50 millisieverts
(mSv is the unit commonly used to measure the effective dose in
diagnostic medical procedures), which is about 16 times the current
annual average for Americans from medical exams and about 21 times
above the average natural background effective dose in the USA. But
these numbers need to be analyzed with care. There is a controversy
between scientists if levels below 50 mSv can be considered as safe
and about the real (and statistically proven) rest-risk of low
radiation exposure.
The most widely used mathematical model in estimating radiation risk
is known as the linear-nonthreshold dose-respond model. This model
assumes that there is no safe dose of radiation and that there is a
linear and direct relation between cancer risk and genetic damage with
radiation exposure. But this model is in discussion since a long time.
For some scientists the linear model is the best way to estimate
radiation risk, but for others there exist a threshold below which
radiation poses no hazard to health.
It is not difficult to identify the most important sources of man-made
or anthropogenic radiation. Most of the collective dose from
diagnostic radiology comes from procedures such as CT, interventional
radiology and barium enemas. Advances in radiological diagnostic
technology have radically transformed medical practice in recent years
and there has been a rapid increase particularly in the application of
CT. Effective dose estimates of CT scans and nuclear medicine studies
are in the range of 10 to 25 mSv for a single study, which is about
100 times larger than those from conventional radiological procedures
such as chest x-rays. Although CT scanners contribute to only 12
percent of all medical radiation procedures, the number of CT scans is
on the rise. In the United States for instance, no more than 3 million
studies using CT were performed in 1980 and in 2006 this number was
already above 60 million. Overall, the mean effective dose in the US
from all medical x-rays has increased about seven-fold over this
period and the situation in Europe is not very different. There are
several scientific studies proving a relationship between small
radiation doses and cancer formation.
One of these studies, already published in the year 2000 (Spine, Morin
Doody et al, Volume 25(16) August 15, 2000), was conducted with 5,573
females aged 20 and younger from 14 orthopedic medical centers in the
United States who had been diagnosed with scoliosis between 1912 and
1965. Scoliosis is a medical condition in which a person?s spine is
curved from side to side, and may also be rotated. The goal of the
study was to evaluate breast cancer mortality patterns among women
with scoliosis and the risks associated with diagnostic radiographic
exposure. Doody and coworkers showed that exposure to multiple
diagnostic radiographic examinations during childhood and adolescence
may increase the risk of breast cancer among women with scoliosis.
Even if this study addresses radiology exams taken on older
technology, the issue is still relevant, as scoliosis patients usually
receive repeated radiographic exams and CT scans for therapy and
treatment. As scoliosis generally is diagnosed even before
adolescence, these susceptible young patients are already exposed to
relatively high radiation doses during their growth period.
As discussed in an other recently published study (Hall et al.,
British Journal of Radiology 81, 362-378, 2008), the relevant organ
doses during CT scans are in the range for which there is now direct
credible epidemiological evidence of an excess risk of cancer, without
the need to extrapolate risks from higher doses. However, even for
high-dose radiological procedures, the risk to the individual patient
is small, so that the benefit/risk balance is generally in the
patients? favour. Concerns arise when CT examinations are used without
a proven clinical rationale, when alternative modalities could be used
with equal efficacy, or when CT scans are repeated unnecessarily.
According to this study, it is assumed that about one-third of all CT
performed in the US could be avoided using alternative diagnostic
tools. According to Hall, at this time, the benefit/risk balance for
any of the commonly suggested CT screening techniques has yet to be
established.
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