Radiation doses in Hiroshima in 1945 - New Sci. letter

["Franta, Jaroslav" <frantaj@aecl.ca>]

http://www.newscientist.com/letters/letters_22524.html
Radiation doses
Your Newswire item "It's never safe" (10 June, p 19 ) was misleading in
several respects. 
The Federal Court of Australia did not rule "that two soldiers died of
cancer because they were exposed to low levels of radiation while occupying
Hiroshima in 1945". The court upheld an earlier decision of the
Administrative Appeals Tribunal (AAT) that a possible link existed between
the soldiers' cancers and their exposure to radiation. 
I did not actually tell the federal court anything and I did not participate
in its proceedings. In 1997, I provided evidence to the AAT, some of which
was quoted in the court's decision in 2000. Your Newswire item
misrepresented my evidence by quoting my words "Even extremely low doses
have an associated risk" out of context. The court's decision quoted me
correctly, saying: "The estimation of risks at low levels of radiation
involves an assumption that all doses of radiation, even extremely low
doses, have an associated risk which increases with increase in dose." 
I believe that the above assumption leads to substantial overestimation of
risks from low doses. Nevertheless, on the basis of this assumption, I
provided the AAT with an estimate that the presumed exposures to about 1
millisievert of radiation at Hiroshima would have caused a fatal cancer risk
of about 1 chance in 20 000 for each of the soldiers. 
I also told the AAT that another possible effect of a low dose of radiation
is to stimulate the immune system and thus provide protection against
cancers, including cancers not caused by radiation. Like the possible
carcinogenic effect, this may vary from person to person. The net effect of
radiation on the incidence of cancer in an exposed group depends on the
balance between the damaging effects on DNA and the protective effects of
stimulating cellular DNA repair. 
However, for an individual who is not suffering from cancer, it is clear
that far and away the most likely health effect of exposure to low radiation
doses (up to at least 200 millisieverts) is no effect at all. 
Don Higson 
Sydney 
New South Wales

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