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Epidemiological musings of a non-biologist





Are cancers dysfunctions of an organism, an organ, a cell or a molecule?  At

which level of analysis should the "cause(s)" of a cancer be sought?  A

common working hypothesis is that ionizing radiation induces cancers by

means of insults to DNA molecules.   But since everyone receiving a

specified dose does not develop cancer, other factors not necessarily

related to radiation  must be intervening.  It seems a lot of things have to

go wrong, in the right order, and at several levels (cellular, tissue and

organism) for cancers to develop.   Each of these factors could (should) be

considered as a confounder in any study of the relationship between

radiation dose and cancer.  



To what extent then do case-control studies really avoid the statistical

weaknesses of ecological studies?  The later looks at average doses to

groups instead of doses to individuals.  But what is the "dose" to an

individual? Depending on the level of analysis chosen, the whole body dose

is the average dose to groups of organs/tissue systems, or to groups of

cells, etc..  But we don't really know which dose is relevant to a

particular cancer.   We assume that dose to the thyroid or the lung is

relevant to the corresponding cancer, but dose  to which cell types in those

organs are important?  How is the average dose to the organ related to the

doses to individual cells/cell types?  Doesn't't a study which focuses on

the organ doses to individuals suffer from an "ecological fallacy" when

viewed from the cellular level? 



It is my view that epidemiological studies will never answer the LNT

question.  We must first have a comprehensive theory of cancer before we can

understand the relationship between cancer and radiation.  Epidemiology has

done all it can by establishing an association.  It is incapable of anything

more.



Clayton J. Bradt, CHP

Principal Radiophysicist

NYS Dept. of Labor

Radiological Health Unit

voice: (518) 457-1202

fax:    (518) 485-7406

e-mail: usccjb@labor.state.ny.us



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