[cdn-nucl-l] Boreham, Scientists find low-dose radiation a benefit; Fw: Brenner/Hall paper on CT scans an hypothetical cancer risks

["Jerry Cuttler" <jerrycuttler@rogers.com>]

Nice article ...

http://www.thespec.com/article/290638

Scientists find low-dose radiation a benefit

Doug Boreham

The Hamilton Spectator  (Dec 3, 2007)

In a disturbing study published recently in the New England Journal of 
Medicine, U.S. researchers claimed that 2 per cent of all cancers in coming 
decades will be caused by routine diagnostic CT (computed axial tomography) 
scans.

(The report, by two researchers at Columbia University, said the average 
American's total radiation exposure has nearly doubled since 1980, largely 
because of CT scans. About 62 million CT scans were done in the U.S. last 
year, up from three million in 1980. More than four million were on 
children. CT scans use X-rays. MRI and ultrasound procedures do not.)

There are a number of biological issues that make the type of estimation in 
the Columbia University report inappropriate.

For decades, scientists have been trying to estimate cancer risk associated 
with low-dose exposure by estimating the risk from very high-dose exposure. 
The fact is, it is difficult to estimate risk from high, acute exposures 
down to very low exposures without solid scientific data to support the 
conclusions.

Researchers at McMaster University, for instance, are involved in studies 
focused on the actual biological risks associated with low- and very 
low-dose exposures.

There are many biological reasons why risk extrapolations from high doses 
are not consistent with real risks at low doses.

First, cancer risk estimates from high-dose exposures come from 
epidemiological data from atomic bomb survivors. Radiation-induced cancer 
risk in a war-torn population of Japanese people 62 years ago is vastly 
different than cancer risk in North Americans today.

It is known even today that cancer risks between the two populations are not 
similar because of different genetic backgrounds and environments, 
regardless of radiation exposure. Adding radiation to the equation only 
compounds the difficulties of comparing cancer risks between the two 
populations.

Cancer risk increases when the doses are high and acute, whereas most 
medical procedures use low dose, from which no increased cancer risk was 
observed in the A-bomb survivors. Therefore estimating cancer risk in a 
modern North American population exposed to very low-dose radiation based on 
data from high-dose exposures in A-bomb survivors is almost impossible.

In cancer risk estimations, it is assumed that all doses of radiation are 
risky and the risk is simply proportional to the dose. However, there are 
hundreds of scientific publications to show this is not the case.

At low doses, biological response mechanisms can eliminate minor damage 
caused by low-dose radiation and restore things back to normal with no 
associated risk.

At high doses, other mechanisms are used as an emergency defence for 
survival but these systems tend to be error-prone and consequently increase 
cancer risk.

Overall, biological mechanisms responding to low doses are different than 
those at high doses. Therefore, assuming the biological risk is the same at 
all doses is biologically flawed.

There are also hundreds of scientific reports that support the idea that 
low- dose radiation is a necessary environmental agent required for life. 
Our research at McMaster University has shown that low doses can have 
beneficial effects to living organisms, and a large research study is 
currently under way to test the idea that low-dose CT scans actually reduce 
cancer risk.

Studies that investigate risk based on total dose are questionable if the 
total doses have been additive, like adding up the entire dose from several 
CT scans, because evidence supporting the idea that total risk is also 
additive is lacking. It's like taking a bottle of medicine all at once 
(which can be harmful) as opposed to taking small doses of it over a period 
of time (which can be beneficial).

If a radiation dose is spread out over a period of time (split or 
fractionated), like multiple CT scans done over a period of time, the 
biological consequences are known to be reduced because allowing time 
between the exposures allows cellular repair processes to eliminate the 
effects of the prior dose. So the risk is not proportional to the total 
additive dose.

Therefore assuming that the total additive dose from multiple CT scans, 
which is the high total dose required to make the calculated estimated 
cancer risk from A-bomb survivor data, has the corresponding additive 
biological risk may not be accurate.

Also, there are many published reports, other than those on A-bomb 
survivors, in populations exposed to low doses of radiation comparable to 
doses from CT scans, which show cancer mortality is not increased at these 
doses.

Based on actual biological scientific evidence, and not calculated 
extrapolation, an opposite conclusion about CT cancer risk is equally 
plausible. That is, cancer risk in North America may be reduced by 2 per 
cent over the coming decades because of low-dose medical CT exposures.

Studies that warn of increased risk based on calculations from high-dose 
extrapolation from any genotoxic agent should be viewed with caution, 
considered hypothetical, and also potentially detrimental since 
misinformation can sometimes cause undue harm.

Doug Boreham is an associate professor in the department of medical physics 
and applied radiation sciences in the McMaster University Institute for 
Applied Radiation Sciences.


----- Original Message ----- 
From: Scott, Bobby
To: howard long ; Jerry Cuttler ; Carmel Mothersill
Cc: 2007.aapm@aapm.org
Sent: Monday, December 03, 2007 6:10 PM
Subject: FW: Brenner/Hall paper on CT scans an hypothetical cancer risks
-------------------------------------

From: Scott, Bobby
Sent: Monday, December 03, 2007 11:32 AM
To: 'Metting, Noelle'; 'Cyndi Jones'; 'kooyoomjian.jack@epamail.epa.gov'; 
'Classic, Kelly L.'; 'Dicarlo-Cohen, Andrea (NIH/NIAID) [E]'; 
'stoneh@mail.nih.gov'; 'edouple@nas.edu'; 'Hirsch, Roland'; 
'david.thomassen@science.doe.gov'; 'kooyoomjian.jack@epamail.epa.gov'; 
'Quill, Helen (NIH/NIAID) [E]'; 'Coleman, Norman (NIH/NCI) [E]'
Cc: 'Pam.Sykes@flinders.edu.au'; 'Edouard Azzam'; 'brenda laster'; 
'brenda.rodgers@ttu.edu'; Edward J. Calabrese; 'Ludwig E. Feinendegen'; 
'Dietrich Averbeck'; 'Georg Bauer'; Douglas Spitz; Gayle E Woloschak ; 
'hsducoff@uiuc.edu'; 'Eleanor A Blakely'; 'lynn.hlatky@tuffs.edu'; 
'clsanders'; 'Lyndy Volker'; Galina V. Zhuntova
Subject: Brenner/Hall paper on CT scans an hypothetical cancer risks

Dear Colleagues:

You are probably aware of the media coverage of the new paper by D.J. 
Brenner and E.J. Hall entitled "Computed Tomography - an increasing source 
of radiation exposure" that was published in The New England Journal of 
Medicine 357:2277-2284, 2007. Brenner and Hall extrapolated from high-dose 
cancer data associated with the atomic blasts that took place in Hiroshima 
and Nagasaki to low doses of X-rays from CT scans in clinical settings in 
the United States, via using the linear no-threshold (LNT) model. The atomic 
detonations involve gamma rays, neutrons, blast propelled projectiles, and 
thermal waves. The population response involved combined injuries (wounds, 
thermal burns, neutron/gamma-ray induced damage) and recovery in devastated 
cities.  Without adjusting for such combined injuries, adverse environmental 
effects, differences in genetic susceptibilities of the Japanese and U.S. 
populations, and using hypothetical low-dose cancer risks, Brenner and Hall 
calculate that in coming decades, 2 per cent of all cancers in the U.S. will 
be caused by routine diagnostic  CT scans.

Attached is an article published today in The Hamilton Spectator that 
presents a different perspective on low-dose radiation risks associated with 
CT scans. The article was written by Doug Boreham of McMaster University and 
is entitled "Scientist find low-dose radiation a benefit".  I thought you 
may like to know about the article.

Best wishes,
Bobby R. Scott, Ph.D.
Senior Scientist
Lovelace Respiratory Research Institute
2425 Ridgecrest Drive SE
Albuquerque, NM