New York Times Article
despnh at SOUTH-01.NOVELL.LEEDS.AC.UK
Thu Nov 29 08:21:01 PST 2001
You are quite right.
One of the things that never ceased to surprise, and frustrate me,
during my time as Editor of DMFR, was the reluctance of North
American contributors to adopt SI units, 20 years or more after the
Date sent: Wed, 28 Nov 2001 16:03:02 -0600
Send reply to: Oral Radiology Discussion Group <ORADLIST at LISTSERV.UCLA.EDU>
From: Byron Benson <BBenson at TAMBCD.EDU>
Subject: Re: New York Times Article
To: ORADLIST at LISTSERV.UCLA.EDU
Thanks for posting this article, Mel. I was a little surprised that the
radiation doses were expressed in millirems rather than Sieverts. I thought
SI units were the norm.
Byron W. (Pete) Benson, D.D.S., M.S.
Professor, Oral & Maxillofacial Radiology
Baylor College of Dentistry
Texas A & M University System Health Science Center
3302 Gaston Avenue
Dallas, Texas 75246
Telephone: (214) 828-8393
Telefax: (214) 874-4551
Email: Bbenson at tambcd.edu
From: Mel Kantor [mailto:mkantor at UMDNJ.EDU]
Sent: Wednesday, November 28, 2001 3:17 PM
To: ORADLIST at listserv.ucla.edu
Subject: New York Times Article
Our colleague, Earl Warman, brought this to my attention. I think the
members of the list might be interested as well.
November 27, 2001
For Radiation, How Much Is Too Much?
By GINA KOLATA
In their efforts to protect Americans from the hazards of radiation,
federal agencies have found themselves in a quandary. People are
constantly exposed to radiation from natural sources - from cosmic rays,
radon seeping out of the earth and radioactive substances in soil,
water, food and even from potassium in the human body itself.
Compared with this radiation, the amounts coming from human efforts like
nuclear plants are, relatively, minuscule. So, the question is, How
closely must this radiation be regulated?
Up to now, regulators have typically acted as if every bit of excess
exposure is potentially hazardous. But some scientists question this
The issue is becoming increasingly pressing as more than 100 nuclear
power plants are being relicensed so they can continue to operate. At
the same time,
the country faces a growing predicament of what to do with nuclear waste
from power plants and weapons sites.
"The issue rages because we are regulating doses that are lower than the
natural background of radiation," said Dr. Arthur Upton. A radiation
expert and former director of the National Cancer Institute, Dr. Upton
is a professor of environmental and community medicine at the University
of Medicine and Dentistry of New Jersey.
In a report last year on radiation standards, the General Accounting
investigative arm of Congress, said: "The standards administered by
E.P.A. and N.R.C. to protect the public from low-level radiation
exposure do not have a conclusive scientific basis, despite decades of
The situation is further confused, experts say, because regulatory
standards are a
The Environmental Protection Agency advocates a standard for all
exposure from a single source or site at 15 millirem a year, with no
more than 4
coming from ground water. A standard chest X-ray, in comparison, gives
about 10 millirem to the chest, which is equivalent to 1 or 2 millirem
to the whole body. The Nuclear Regulatory Commission sets its acceptable
level of radiation exposure from any one source at 25 millirem a year.
In contrast, the natural level of background radiation in the United
States, on average, is about 350 millirem a year, and in some areas of
the country it is many times higher than that.
In New York, for example, people absorb about 100 millirem of radiation
each year from cosmic rays alone, said Dr. John Boice Jr., a radiation
expert, who is the scientific director of the International Epidemiology
Institute in Rockville, Md. In Denver, exposure from cosmic rays
averages 200 millirem a year, he said, and natural variation in
radiation exposure is many times the amounts of radiation that are being
disputed by regulatory agencies. "We eat, breathe and drink low levels
of radiation," Dr. Boice said.
At the same time, said Dr. Fred Mettler, chairman of the radiology
the University of New Mexico medical school, major medical sources of
radiation, like CAT scanners, have fallen outside the purview of any
regulatory agency. "A whole lot of places aren't regulated at all," Dr.
Mettler said. "It's a bit of a nightmare."
"When you look at the exposure of the population from radiation, about
two-thirds is due to natural background and about 15 percent is due to
your friendly doctors and chiropractors," Dr. Mettler said. "Everything
else is, to
tell you the truth, very minimal. Less than a couple of percent is from
all the nuclear reactors and all the research industry."
But, asked Dr. John Evans, a risk analyst at the Harvard School of
Public Health, Why should the level of background radiation matter to
the question of how much
additional risk from human-generated sources is acceptable? "Why isn't
relevant question, How much of this risk can be mitigated at what cost
to you?" he
The quandary over how to set radiation levels does not result from a
research or analysis, scientists say.
"Radiation's effects on people have been studied for over a century,"
said. "There's a vast literature. There are probably more studies on the
harmful effects of radiation than for any other toxic or noxious agents
in the environment."
And as scientists studied radiation, committees to evaluate the data
"We have national and international standing committees that
periodically review the world's literature on ionizing radiation," said
Dr. Boice, who is a member of many such groups. "At the International
Committee on Radiological Protection, we just celebrated our 75th
anniversary and we meet two or three times
a year." Then, he said, there is the United Nations Scientific Committee
on the Effects of Atomic Radiation. "That started in 1955," Dr. Boice
said. "We meet every year in Vienna and we publish volumes."
In the United States, the Environmental Protection Agency, the Nuclear
Regulatory Commission and the National Council on Radiation Protection
Measurements wrestle with the radiation standards question, and the
Academy of Sciences has been called upon periodically since the 1950's
weigh in with its committee, called the Biological Effects of Ionizing
committee. The Department of Energy and the National Institutes of
conduct extensive research.
The science has grown rapidly. In 1980, Dr. Boice set up the radiation
epidemiology section at the National Cancer Institute with just a
researchers. Now, he said, while he moved on to form the International
Epidemiology Institute, which conducts research for industry and the
government, the cancer institute's radiation department is no longer a
section, it is a branch, and one of the largest branches there, with
hundreds of scientists.
"A lot of people say, `Gee, we don't know a lot about the risks of
radiation,' " Dr.
Boice said. "I say: `We know a whole lot. We've studied populations all
world since the turn of the last century. We know what happens at high
doses. We know what happens at medical doses. And we know that at low
doses the risks are low. The controversy is just how low are they. Are
they really low or are they really, really low?' "
As with other toxic substances in the environment, the stricter the
more it costs to meet them.
The G.A.O. report last year, which had the subtitle "Scientific Basis
and E.P.A. and N.R.C. Disagreement Continues," gave some examples of the
costs of complying with standards setting different levels of radiation.
The cost of cleaning soil around reactors and nuclear weapons facilities
could range from thousands of dollars to more than $100 million,
depending on whether the
standard was an exposure of 15 or 25 millirem a year, the report said.
(Page 2 of 2)
The report said that for groundwater, the cost of going from the
Nuclear Regulatory Commission's limits of 25 millirem a year to the
level that the Environmental Protection Agency wants could be billions
Scientists usually rely on a mathematical model in estimating radiation
risk. The most widely used model is known as the linear-nonthreshold
dose-response model. It assumes that there is no safe dose of radiation
and that the risk of getting cancer or genetic damage increases along
with radiation exposure.
"For better or worse, that is our model," said Stephen Page, the
director of the environmental agency's office of radiation and indoor
air. And with that model, he said, "the E.P.A. has tried to be as
protective as possible." The agency, he added, uses that model to make
sure the risk from radiation is within the allowable range from toxic
chemicals, 1 in 10,000 to 1 in a million chance of developing cancer.
Some say that the linear model is the best way to estimate radiation
risk, but others say that there is, in fact, a threshold below which
radiation poses no hazard to health. And still others say that low doses
of radiation are actually beneficial.
The linear hypothesis had its origin in 1927, when the geneticist Dr. H.
J. Muller published a paper on his work eliciting gene mutations in
fruit flies by bombarding them with radiation from X-rays. In a paper
published in the journal Science, Dr. Muller showed that the number of
mutations in fruit flies was proportional to the dose of X-rays that had
struck the insects.
"He said: `Aha! There's a linear relationship,' " said Dr. Dade W.
Moeller, a radiation expert and professor emeritus at Harvard who runs a
consulting company, Dade Moeller & Associates in New Bern, N.C. Yet, Dr.
points out, those studies by Dr. Muller used very high doses of
radiation, and he
elicited gene mutations, not cancer. But the idea that radiation's
were directly proportional to its dose caught hold and soon was being
used to predict cancer cases. The difficulty was in demonstrating it.
The risks of getting cancer from exposure to radiation increase with
dose. But since a third of all people get cancer anyway, at some time in
their lives, the problem is to find evidence that low doses of radiation
cause cancers that
would not have otherwise occurred. Even for people exposed to large
doses, like the 80,000 to 90,000 survivors of the atomic bombs exploded
Hiroshima and Nagasaki, it has been hard to find excess cancers.
"They were exposed in 1945 and nearly half are still alive," Dr. Moeller
Dr. Mettler said the latest data show that 12,000 of these atomic bomb
survivors had died from cancer. He said the number of excess cancers in
the group is about
700. Those data, Dr. Mettler said, show that there is a small risk of
cancer with an exposure of tens of thousands of millirem of radiation.
"There's a group that says that if you can't see it, it doesn't exist,"
Dr. Mettler said. "Then there's another group that says, `That's nice,
but it doesn't mean it doesn't happen.' "
Now, some scientists even say low radiation doses may be beneficial.
They theorize that these doses protect against cancer by activating
cells' natural defense mechanisms. As evidence, they cite studies, like
one in Canada of tuberculosis patients who had multiple chest X-rays and
one of nuclear workers in the United States. The tuberculosis patients,
some analyses said, had fewer cases of breast cancer than would be
expected and the nuclear workers had a lower mortality rate than would
Dr. Boice said these studies were flawed by statistical pitfalls, and
when a committee of the National Council on Radiation Protection and
Measurement evaluated this and other studies on beneficial effects, it
not convinced. The group, headed by Dr. Upton of New Jersey, wrote that
the data "do not exclude" the hypothesis. But, it added, "the prevailing
generally been interpreted as insufficient to support this view."
In the meantime, the regulatory agencies are at a stalemate, continuing
to disagree on radiation standards. And the committee reports and
committee meetings on radiation standards go on.
A recent report, issued in June by the National Council on Radiation
Protection and Risks, is 287 pages long and devoted entirely to
evaluating the linear-nonthreshold model. It explains that the council
"has sought to leave no
significant aspect of the subject unaddressed."
For lack of a better model, it recommends keeping the linear one. "There
is not conclusive evidence on which to reject" the model, the report
says, adding that "it may never be possible to prove or disprove the
validity of the linear nonthreshold assumption."
Consultant Dental Radiologist
Editor, Dentomaxillofacial Radiology
Leeds Dental Institute
Leeds LS2 9LU
Tel +44 (0)113 233 6214
Fax +44 (0)113 233 6165
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