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decreased with mitotic conpetence, then estimates of carcinogenesis based
on a fictitious averaging of a local inhomogeneous dose over 4 much larger
volume would be necessarily conservative.
Since radiation carcinegensis
can, and in. fact, does increase to anomalously large values while the mitotic
-ompetence bacomes vanishlingly small, the. fictitious averaging of dose
over larger volumes is not necessarily ‘conservative.
Instead it would
appear that an intense local dose of ionizing radiation can be a more
efficient carcinogen than a diffuse tissue exposure with the same typ2 of
ionizing radiation and the same total energy.
The above then implies that
averaging of dose over larger volumes may be far from conservative.
It is obvious that as a local exposure becomes more intense, a
stage must finally be reached where the carcinogenic efficiency of the
exposure (con a per unit energy basis) is reduced.
to previous arguments.
This is not pertinent
It would, however, be important to know the
characteristics of the most carcinogenicly efficient exposures.
The following excerpt taken from the BEIR report (p. 95) summarizes
the state of knowledge concerning the causation of cancer (emphasis added):
"Although the mechanisms of carcinogenesis, or of
vadiztion carcinogenesis in particuiar, are not fully
Known, available information implies that most, if not
ali, types of cancer develop as a resuit of the combined
effects of multiple factors. These causative factors
may include: prezygotic (inherited) mutations of
chromosomal aberrations, which can spread during develop-
ment to many kinds of cells; somatic cell mutations or
chromosomal aberrations, which can be acquired at any
time after conception; changes resulting from the action
of viruses; and changes in systemic growth factors (e.g.,
depressed immune competence, hormonal imbalance) and
in local tissue requlation (disorcanization,damage),
Such as may result Tron diseases other than cancer or
from advancing age (1).
“Altncugh point mutations, chronosanal abborations,
and other chances at the celluler and molecular Icvel
may require only sual] coses, tissue cisoraanization end
.