:
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2 cmined
digh-Level Exposure
je and
The above discussion has referred principally to “low-level”
Thus severe
at
exposure,
The differences between low- and high- level exposure are shown
in Figure 8, for a low-LET radiation only.
all.
horizontal and then diagonal,
is for the specific energy (cell dose), vs.
the absorbed dose to the organ.
of cells hit,
{.e.,
The heavy solid line, first
The upper dotted line Is for the fraction
the nunber of hits per cell, as a function of organ
absorbed dose.
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Absorbed dose/Gy
28
am
the
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atinuous
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3 is
Fig. 8 Relationship hetveen the specific energy, 1.e., cell dose, as well
as the fraction of affected target-containing volumes within a cell, and
the organ absorbed dose in Gy.
Note that at large crgan doses, cell and
organ dose approach being equal, and the variance becomes small. At low
organ doses, the expectation value of the cell Jose becomes constant,
although the variance of that mean {a quite large.
At these low organ
doses, it is only the fraction of cells hit and dosed that can increase
with organ absocbed dose.
Where
the solid line becomes diagonal,
the upper large-exposure
pact of the curve, each cell has received a large number of hits.
If one
calls the summation of energy densities from these multiple hits the "cell
dose",
then it is clear
that even though
that “dose” vary greatly in size,
Snaller and smaller.
cell TCV, Cs 22
ght better beey
in
There
risk for each discrete hit.
the
individual hits constituting
the variance of
is then no reason
It fis adequate,
tions *
-~221-
the mean will become
to evaluate separately
for practical reasons,
the
simply