Gibbs, S Julian
s.julian.gibbs at VANDERBILT.EDU
Thu Aug 19 08:35:37 PDT 1999
Some items of interest from the RADSAFE listserver:
Date: Wed, 18 Aug 1999 14:19:55 -0500
From: Maury Siskel <maury at webtexas.com>
To: radsafe <radsafe at romulus.ehs.uiuc.edu>
Subject: Interesting view of leukemia.
Message-ID: <37BB075B.4E59D7C at webtexas.com>
Researcher Says Childhood Leukemia Is Caused By Infection
August 16, 1999
LONDON (The Independent) - Childhood leukemia is caused by
an infection and not by radiation or environmental
pollution, according to one of the world's most eminent
Sir Richard Doll, who first established the link between
smoking and lung cancer, has given his full support to a
controversial theory that cancer clusters, including those
near to nuclear installations, are the result of a virus or
other infectious agents.
In an article for the British Journal of Cancer, Sir
Richard says that new research into the reasons why some
children develop the blood cancer has now established the
cause as an infection by an as-yet unidentified agent.
"What I'm saying, in layman's terms, is that we believe
that the principal cause of childhood leukemia is an
infection of some sort. We can't say what it is but we now
know where we've got to look," Sir Richard said Friday.
(British cancer specialists hailed the new research as a
major step forward in helping them to develop a vaccine.)
For two decades scientists have been trying to explain why
leukemia in children - an exceptionally rare disease -
clusters around certain industrial sites, in particular the
Sellafield nuclear reprocessing plant in
Cumbria. Several investigations by leading cancer
and radiobiologists, have failed to establish a link with
radiation or any
other single factor, such as chemical pollution.
However, a theory developed by Professor Leo Kinlen, a
cancer epidemiologist at Oxford University, has gradually
become the most convincing explanation of the clusters.
Kinlen, who is funded by the Cancer Research Campaign and
has no financial ties with the nuclear industry, believes
childhood leukemia is
caused by viruses or other infectious agents being
introduced into a local community by the mass movement of
migrant workers. Some children may be more susceptible to
developing leukemia as a result of being exposed to an
infectious agent that may have little or no effect on other
children, Kinlen suggested.
Heather Dickinson and Louise Parker of the Children's
Cancer Research Unit at the University of Newcastle have
produced a computer model of the Kinlen hypothesis and
found that it can correctly predict the incidence
of leukemia according to the amount of population mixing involved.
Sir Richard believes this is the final piece of the jigsaw
Professor Kinlen's hypothesis as the most likely
explanation for childhood leukemia clusters around
Sellafield and elsewhere.
"My view now is that Kinlen's hypothesis should be
considered as established. It indicates an infective
cause," he said. He criticized the
government's Committee on the Medical Aspects of Radiation
in the Environment for downgrading the Kinlen hypothesis
when it published its fourth report in 1996.
Sir Richard, who is now retired but takes an active
interest in cancer epidemiology from his base at Oxford's
Radcliffe Infirmary, said scientists can now concentrate on
trying to find the infective agent responsible. "It is
possibly a common virus which only in special circumstances
actually gives rise to leukemia, rather than some rare one
- but that's speculation. All I can say is that we're now
convinced that it must be infection," he said.
Professor Kinlen said he could not comment on the findings
until they are published Monday in the British Journal of
Copyright 1999 The Independent. All rights reserved.
Maury Siskel maury at webtexas.com
In these sentiments, Sir, I agree to this Constitution with
all its faults, if they are such;
because I think a general Government necessary for us, and
there is no form of Government but
what may be a blessing to the people if well administered,
and believe farther that this is
likely to be well administered for a course of years, and
can only end in Despotism, as other
forms have done before it, when the people shall become so
corrupted as to need despotic
Government, being incapable of any other.
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Date: Wed, 18 Aug 1999 16:12:14 -0400
From: Tonry Louie L MAJ <Louie.Tonry at se.amedd.army.mil>
To: "'Bala, Vaidy LAB'" <vaidy.bala.lab at govmail.gov.sk.ca>,
Subject: RE: Errors in Dental X-Ray Eqt Test using
Keithley's TRIADsystem Message-ID:
<AB29E2317FB0D211A4B400805FA7E6F4163894 at DASMTHFDZ002.AMEDD.ARMY.MIL>
There are a number of ways to determine what's going on
with the kVp. I agree the best way is to use the waveform.
When you look at the waveform, you will see a
representation of the kVp and how it changes over time.
If the kV is unstable over time or you are getting an
unusually high peak on the lead edge, this can result in
errors in the reported kV.
Some suggestions that might help. Often with dental
systems, it's hard to get a complete coverage of the
detectors active area. We have often seen very high kVs
when we expose one detector and not the other. If
you understand how the detector works this makes sense.
The kV detector has two detectors; one is a reference
detector (with a reference filter) and the other is the
measurement filter (with an appropriate filter for the
energy of interest). The voltages from these two detectors
are compared and the calibration table is referenced to
determine the actual kV. If the reference detector isn't
fully exposed, the measured voltage will be too low and the
ratio will be too high leading to a higher reported kV.
Try exposing the detector at different distances and see if
A second suggestion is to use a higher technique. Some
times if the exposures are too low, the signal from the
detectors is inadequate to give a good reading. This sort
of counters what I recommended above but try moving the
tube head closer to the detector.
Here's another technique you might want to use. Get an old
x-ray cassette and tear out the intensifing screen. The
screen can then be used to visualize the x-ray field size
during setup of your equipment. This way you will know if
you've indeed got adequate coverage of the detectors prior
to measurement. I always have one in my case for just this
The biggest problem when measuring dental kV and time
non-invasively is the way the manufacturer's make their
x-ray units. If you compare the output waveform and the kV
waveform you will see what's actually happening. There is
a preheat time built into most dental x-ray systems.
During this time, kV is applied to the x-ray tube but the
mA isn't. However, there are still electons available on
the filament which will produce x-rays. The intensity is
very low BUT the multi-meters are sensitive enough that it
will 'see' them. Since during this time, the kV is
stabilizing (one of the reasons this is done), often you
will see varing kV. Once the mA is applied, the kV is
usually stable and usually will be pretty accurate.
I've attached a waveform picture for you to look at. This
is a 320 mS exposure from a Heliodent 70 x-ray system. The
top graph is the kV and the bottom is the output. As you
can see, the kV waveform starts well before any apprecable
output is recorded. This is the preheat period. Once the
mA is applied to the filament, the output jumps up and the
kV flattens out.
I've used the PMX many times. It's pretty good but has
some disadvantages. It's a little hard to learn to use and
the software is DOS based which I don't like. They tell me
that a windows based software is due to be released this
summer. I hope so since I like the PMXs flexability.
Hope this is helpful. If you have other questions, let me
S. Julian Gibbs, DDS, PhD Voice: 615-322-3190
Professor of Radiology FAX: 615-322-3764
Dept. of Radiology & Radiological Sciences
Vanderbilt University Medical Center
Nashville TN 37232-2670 Email:j.gibbs at vanderbilt.edu
Tell me and I forget; teach me and I remember; involve me
and I learn.
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