THE SHORTER-TERM BIOLOGICAL HAZARDS OF A FALLOUT FIELD
the weight effect in groups of male Sprague-Dawleyrats
given 4,3, or 16r 6 days per week beginning at 53 days
of age [16]. Weight effect, H(#), is defined as E(Q =log
CQ log RY —log Cotlog Ry where logarithms are
in several physiologic systems, and the
degree of lethal injuryis a sum of these.
2. Injury from other causes, and in par-
ticular accumulatedinjury due to ageing
processes, also contributes additively
to the lethal injury
Figure 24 givea the result of a
graphical differentiation of the H(® curve in Figure }
‘nypotheses1s limited, as is discssed balow.
DIST r/day
Wp ()-
025)
20
WEIGHT EFFECT Ete}
he
685 r/doy
|_——>
>
3
A E0G We )]
°
3
0.1
i These are postulated properties of the model system, They are Aypotheses about the properties of reel blological systems, Their value as
DERIVATIVE OF
DAILY DOSE RESPONSE
1. Radiation in general produces injury
Figure 28, the same measure of effect is applied to the
at 53 days of age.
g
(14, 17, 18].
to base 10, C(f) is control weight at time t, R(t) is
weight of irradiated animals at time t, and Cy and Ro
are mean Weights over the pretreatment period. In
eight response of male rats given a single dose of 200 r
7O)
°
a
3°
Figure 1 shows
The properties of the lincar model may be
expressed in the following set of postulates
nl
An example of an experimental test of the additivity
hypothesis is given in Figures land 2.
OTS,
with the size of the dose,
6
pendent of the effects of the other incremenis.
1.002
232 3 3
about the combined effect: of a sequence of
dosages is the additive hypothesis which states
that the effect produced at a given time is the
sum at that time of the effects of the dosages
given separately in their proper positions in
the sequence. This implies that every incremeni of dose produces an effect that is inde-
1.003
loos
depth of the minimum and alse with respect to the
W,
an injury response with a characteristic amplitude and time-course. The simplest hypothesis
stable vatue reached after 60 days postirraciation,
This comparison is not quantitative, because of the
difficulty in obtaining reproducibility of weight responser after siugle doses of 200 r or less, However,
the comparison of hematologic respouses to single and
daily doses yields results of a similar nature, It is
concluded (171 Ghat the responses to simall dases may
be additive, but the departure from additivity inereases
0.005
Wo (tH
them. We knowthat a single dose produces
0.006
2
increments and of the time intervals between
C.007
°°
When several increments of exposure are
given sufficiently close together, the physiologic
response is some function of all the dose
for rais given 161 daily. The daily dose weight curve
van be accounted for on the busis that each daily dose
produces by itself a weight response as in Figure 2A,
Uf the enurves in Figure 24 and 2H agres, the additivity
hypothesis is upheld. There is agreement in overall
amplitude of the firsé peak, and in the presence of two
peaks of effect separated by a minimum at about 14
days, There is disagreement with iespect to the
eo
A GENERAL LINEAR MODEL OF RADIA.
TION LETHALITY
103
QUANTITIVE ESTIMATION OF RADIATION INJURY AND LETHALITY
SINGLE DOSE RESPONSE—L5 OG
102
100
110
120
130
uo
1
TIME - DAYS
Froure 1.—Effect of daily X-ray exposure on weight of growing rats, expressed ag the difference of logarithms of
etperimental and control weights. Upward displacement signifies weight loss in treated groups.
O15)
010)
Osi
TIME (DAYS)
Ficurn 2.—Observed and calculated response of growth curve following single exposure to X-rays. Lower
observed effect of a single dose of 200 7. Upper curve is a graphical differentiation of the curve for daily
13.7 r/day in Figure 1.
curve ia the
exposure at