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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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