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Re: Scary X-rays?!
The risk-estimating coefficients are, also, linearly extrapolated from very
high doses/doserates to low doses/doserates. Does anyone really believe
that the risk for a population of 100,000 people, receiving 10,000,000
person-rem (100 rem each), as a high doserate, is the same as that for a
population of, say, 10,000,000 people receiving the same collective dose,
at relatively low doserates? Let's not even open the question of hormesis.
chris a.
alstonc@odrge.odr.georgetown.edu
At 09:38 AM 7/14/99 +1000, you wrote:
>Hi all,
>
>Regarding the CT doses from abdominal examinations the following survey data
>giving effective doses may be useful:
>
>NRPB (UK) 1991 7.6 mSv
>ARL (Australia) 1997 17.5 mSv
>NRL (New Zealand) 1992 11.6 mSv
>
>The marked differences may be attributable to changes in the pattern of use
>(eg spiral versus axial scanning, contrast versus no contrast etc). In any
>event for the sake of argument we might take a figure of 20 mSv as the upper
>limit for a CT abdomen. Applying the ICRPs fatal cancer risk factor for the
>whole population of 5%/Sv (see ICRP 60) would give a risk estimate of 10 in
>10,000 not too different from the figure quoted in the article. However,
>the application of such a simplistic risk analysis should be treated with
>great caution. The ICRP risk number applies for equal numbers of both sexes
>and includes all ages. In reality, the population that receives CT scans is
>very much skewed towards the elderly and the cancer risk is probably reduced
>by at least a factor of three and possibly by as much as 10 (see ICRP 62).
>Nevertheless, CT as Joel says, is a high dose procedure and the introduction
>of reference levels is an excellent idea which may help reduce these doses.
>
>
>************************************************
>John Heggie, Ph.D
>Director Dept Medical Engineering & Physics
>St. Vincent's Hospital
>FITZROY VIC 3065
>AUSTRALIA
>
>Ph (613) 9288 4591
>Fax (613) 9288 4347
>Email heggiejc@svhm.org.au
>
>
>> ----------
>> From: Pallas Larry[SMTP:Larry.Pallas@COLUMBIA.NET]
>> Reply To: Pallas Larry
>> Sent: Wednesday, 14 July 1999 2:13
>> To: MEDPHYS@cwis-20.wayne.edu
>> Subject: Scary X-rays?!
>>
>> MedPhysers,
>>
>> The following letter to the Editors of Discover Magazine was printed in
>> the
>> August 1999 issue:
>>
>> The beautiful images shown in "X-ray Stories" [May] demonstrated, as you
>> wrote, "why X-rays retain their usefulness in an age of CT scans, MRIs,
>> and
>> high-tech imaging." The use of CT scans should not be discouraged when the
>> benefits are clear, but it should be noted that CT uses truly scary
>> X-rays.
>> Abdominal CT scans cause 12.5 cancer deaths per 10,000 persons exposed to
>> a
>> single examination, comparable with yearly smoking-induced deaths at 12
>> per
>> 10,000 smokers. Currently, in the United States about 35 percent of all
>> medical radiation exposure now comes from CT scans, which make up about 5
>> percent of all medical examinations that use radiation. This is estimated
>> to
>> cause at least 2,600 cancer deaths in the United States per year. The
>> simple
>> film X-rays shown in the article still retain many advantages.
>>
>> Signed by an MD, FACR from New York
>>
>> I can't believe these statistics and I would like to write a rebuttal.
>> Can
>> anyone point me to some real data? He doesn't say where he got his from.
>> Comments?
>>
>> Larry Pallas
>> Radiation Oncology
>> Swedish Medical Center
>> Englewood, CO
>> Larry.Pallas@Columbia.net
>>
>> *********** ************
>> Frequently Asked Questions (FAQ) for Medphys at:
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>>
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>>
>
> *********** ************
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>
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