clinic or laboratory.
It would appear under these circumstances and in
most experimental conditions that the midline dose, rather than dose
measured in air, would be
the better cummon parameter in terms of which te
predict biologicgl effect.
s
On
this assumption, air dose value should be
multiplied by approximately 1.5 in order
to conpare
their effects te
a
Lituse
f.
of a given air dose from a “point source” beam peometry delivered
Ur.
bilaterally.
th
Furthermore,
the geometry of radiation from a fallout field
is not identical either to the geometry of bilateral point sources or the
spherically distributed sources since the plane source delivers a radiation
largely at a grazing angle.
However,
the total field situation is better
approximated by solid than by plane peometry.
Figure 9 shows depth-dose curves for different types of radiation to
provide an idea of the difference in absorption of energy
throughout a
large animal body thus injury (in the lethal range) to the important target
cell,
the hematopoietic stem cell, which determines whether the bone marrow
will regenerate.
These depth-dose curves are determined in unit density
material using small Sievert chambers implanted at 6 cm intervals in the
phantoms.
The doses are expressed as percent of
the entrance air dose,
Curve A represents the depth-dose curve from 250 kVp x ray.
commonly used energy of radiation in animal studies.
Note,
This is a
the surface
dose ts about 40% greater than the entrance air dose and this falls off
very rapidly with depth in the tissue so
that approximately in the midline
corresponding to wan {it would be 60% of the entrance to the important
target cell,
the hemopoietic stem cell, which determines bone marrow
by a very large factor.
2000 kVp x ray.
|
The curve B shows a simtlar depth-dose curve for?
Curve C is the initial bomb gamma radiation and curve p!
cobalt-60 gamma radiation,
It is evident that for the same air dose,
injury to hematopofetic stem cells scattered throughout the bone marrow
varfe: consicerably and thus would be expected to result in different
lethal
dose curves.
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