[ RadSafe ] Research shows CT and nuclear imaging tests during pregnancy do not boost the risk of childhood cancer

[Alston, Chris]

Prof. Raabe

Maybe I am a little slow here, but, if the slope of the risk is 6% per Gy (100 rad), how could there be an observable increase in risk as low as 0.01 Gy?

Cheers
cja



As you surely already know, beginning in 1956 Alice Stewart  and her 
followers have demonstrated a strong statistical association between 
pre-natal X-rays and childhood cancer in the Oxford Survey of 
Childhood Cancer OSCC .  These data and positions received 
considerable prestige with the review of the data by Doll and 
Wakeford (The British Journal of Radiology, Vol 70, Issue 830 130-139,1997)


Risk of childhood cancer from fetal irradiation

R Doll and R Wakeford
Imperial Cancer Research Fund Cancer Studies Unit, Radcliffe 
Infirmary, Oxford, UK.

The association between the low dose of ionizing radiation received 
by the fetus in utero from diagnostic radiography, particularly in 
the last trimester of pregnancy, and the subsequent risk of cancer in 
childhood provides direct evidence against the existence of a 
threshold dose below which no excess risk arises, and has led to 
changes in medical practice. Initially reported in 1956, a consistent 
association has been found in many case-control studies in different 
countries. The excess relative risk obtained from combining the 
results of these studies has high statistical significance and 
suggests that, in the past, a radiographic examination of the abdomen 
of a pregnant woman produced a proportional increase in risk of about 
40%. A corresponding causal relationship is not universally accepted 
and this interpretation has been challenged on four grounds. On 
review, the evidence against bias and confounding as alternative 
explanations for the association is strong. Scrutiny of the 
objections to causality suggests that they are not, or may not be, 
valid.   A causal explanation is supported by evidence indicating an 
appropriate dose-response relationship and by animal experiments. It 
is concluded that radiation doses of the order of 10 mGy received by 
the fetus in utero produce a consequent increase in the risk of 
childhood cancer. The excess absolute risk coefficient at this level 
of exposure is approximately 6% per gray, although the exact value of 
this risk coefficient remains uncertain.



**********************************************
Prof. Otto G. Raabe, Ph.D., CHP
Center for Health & the Environment
University of California
One Shields Avenue
Davis, CA 95616
E-Mail: ograabe at ucdavis.edu
Phone: (530) 752-7754   FAX: (530) 758-6140
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