Young single-comb white Leghorn cockerels were subjected to single acute doses of either 2.2 GeV protons or 250 kVp X-rays. Since young chickens exposed in the lethal range die within 48 hours of exposure, an hourly tabulation of deaths was recorded for this length of time after exposure. Animals which were exposed to sublethal doses were killed five days after exposure and their major lymphatic organs, (thymus, bursa, and spleen), removed and weighed. In the lethal range, animals exposed to 2.2 GeV protons died sooner than those receiving similar doses of X-rays, but total mortality was similar in each case at similar dose levels. The 48 hour LD sub 50 was determined to be 710 rad. Measured five days after exposure, 50% depression ED sub 50 for lymphatic organs occurred as follows: (1) thymus, 350 rad; (2) pursa, 500 rad, and (3) spleen, 450 rad. In all case R.B.E. values were not different from unity

Montour, J. L.

Shellabarger, C. J.

English

NASA Technical Reports Server

LYMPHATICINVOLUTIONANDEARLY MORTALITY IN THE YOUNG CHICKEN PRODUCED BY
2.2 GeV PROTONS ]
James L. Montour 2 and Claire J Shellabarger 3
Radiology Department, Medical College of Virginia, Virginia Commonwealth Univer-
sity, Richmond, Virginia
Zoology Department, University of Michigan, _nn Arbor and
Medical Department, Brookhaven National Laboratory _, Upton, New York
I. Supported in part by NASA (NsG 214-62)
2. Present Address - RadEology Department, Medical College of Virginia,
Virginia Commonwealth University, Richmond, Virginia
3. Present Address - Medical Department, Brookhaven National Laboratory
4. Brookhaven National Laboratory is supported by the U.S.A.E.C.
Young single-comb white Leghorn cockerels were
subjected to single acute doses of either 2.2 GeV
protons or 250 kVp X-rays. Since young chickens
exposed in the lethal range die within 4_ hours of
exposure, an hourly tabulation of deaths was recorded
for this length of time after exposure. Animals
which were exposed to sublethal doses were killed
flve days after exposure and their major lymphatic
organs, (thymus, bursa, and spleen), removed and weighed.
In the lethal range, animals exposed to 2.2 GeV
protons died sooner than those receiving similar doses
of X-rays, but total mortality was similar in each
case at similar dose levels. The 48 hour LD50 was
determined to be 710 rad. Measured five days after
exposure, 50% depression (ED50) for lymphatic organs
occurred as follows: thymus, 350 rad; bursa 500 rad;
spleen 450 rad. In all case R.B.E. values were not
different from unity.
The total dose from protons of this energy is
comprised of a low LET portion due to dE/dx energy
loss and a high LET portion due to nuclear inter-
actions. R.B.E. values considerably below unity would
be predicted on the basis of dE/dx energy loss alone.
it is suggested, then, that the R.B.E. of that portion
of the dose contributed by nuclear interactions is
very high. If hlgh LET interactions account for only
5% of the total dose_then these interactions could
have an R.B.E. great as 7.
INTRODUCTION
Exposure of young chickens to electromag-
netic radiations at dose rates above 15 R/min.
results in death within 48 hours of exposure
(ref. I) wlth LDso/48 hour values between 700 R
and lO00 R. Vascular leakage, hypotension,
circulatory failure, and renal failure have been
the major characteristics associated with thls
early death. _ref. 2). This is quite different
from the ca_e in mammals where death occurs
8 - 30 days after exposure to similar doses.
Inability of irradiated cells, particularly those
Involved in blood cell formation, to reproduce
is the prime cause of death. Alterations in
vascular permeabillty do occur in mammals, in-
cluding man, after irradiation but these are
generally transitory. Using the young chicken,
it was possible to measure the effectiveness
of 2.2 GeV protons in producing a physiologic
change whose endpoint (death) was easily
6S9
https://ntrs.nasa.gov/search.jsp?R=19720010039 2020-03-17T03:44:29+00:00Z
determined.
Lymphatic organ weight loss in mice has
been shown to be a reproducible measure of radia-
tion dose and has been used as an endpoint for
R.B.E. studies (ref. 3,4). This is also the
case in the young chicken, where lymphatic or-
gan weight loss has been used as a biological
dosimeter and a measure of R.B.E. values for
thermal and fission neutrons. (ref. 5).
In the experiments reported here we have
used these two endpoints, early mortaIlty and
Involution of Iymphatic organs, to examine the
reIatlve blologicaI effectiveness of the 2.2
GeV proton beam of the B rookhaven National
Laboratory Cosmotron.
MATERIALS AND METHODS
Animals - Single comb white leghorn cock-
erels were obtained from Klager Hatchery, Saline,
Michigan, shortly after hatching. Within 24
hours the anlmaIs were transported to the Medl-
cal Department of Brookhaven National Laboratory
and housed, 50 per tier In a standard chick
brooder. Purina starter mash and water were
available ad ]ibitum. Radiation exposures were
p_rformed on the third day of age. The number
oF animals in each experimental group is indi-
cated in Table I and Table II. In the mortality
study, an hourly tabulation of deaths was main-
tained for thirty hours after exposure. Animals
involved in the lymphatic-involution study were
killed and dissected five days after exposure.
Body weights were recorded to the nearest gram
and wet weights of thymus, bursa of Fabricius
and spleen recorded to the nearest 0.] mg. Be-
cause the lymphatic organs of the chick, like
those of mammals, are sensitive to adrenal
80_ )0 1 _ Z 2 2
90_ _0 i Z 2 ? 3 l
s?s 16 l
61_ B l
647 16
690 lo l
?44 16 5 4
?_s _6 5 s
842 16 1 6 3 z
963 16 6 9
loal 16 s B
1206 B _ J i 1
?*bl_ I
F,°_tlo.
1 _ 2 1 Z Z _ _ 29/3O
1 10I_6
2 1_/16
2 8/8
Table II
L)_mphatic Organ Weights Followlng Exposure to
2.2 GeV Protons or 250 KVp X-Rays
B°dy2 3
Dose i N Weight Thymus Bursa Spleen
Control 0 IO 53 _Og 283 106
X-Rays 190 i0 54 247 232 84
380 I0 51 158 170 52
570 i0 49 113 124 41
Protons 112 9 56 242 242 91
188 6 54 231 267 74
230 5 52 185 237 75
299 5 51 143 176 71
316 5 49 171 175 55
344 5 50 148 196 62
386 7 50 146 168 62
406 5 52 150 196 56
435 5 51 139 151 57
437 5 51 112 151 47
498 5 49 96 139 43
522 5 48 98 142 48
551 6 46 83 124 43
576 6 47 i09 140 45
613 7 48 I13 152 42
647 5 47 85 123 34
i. Dose in rads
2. Body weight in grams
3, Organ weights in mg/100 gms. body wight
660
cortlcoid release following stress (ref. 6, 7)
all animals were maintained in the exposure
holders for periods equal to that of the longest
exposure. Half of the control animals were sham-
irradiated in the proton exposure apparatus and
half in the X-ray chamber. No difference was seen
between the two control groups, so they were
pooled for subsequent analysls. To compensate for
variations In body weights between groups, organ
weights are presented as mg/]O0 gm of body weight.
EXPOSURE CONDITIONS
Protons - Proton exposures were carried out
as previously described for mice (ref. 8, 4} end
rats (ref. 9), in a lucite tube 4.5 cm in dla-
meter and 12_1 cm in length. Four chicks were
exposed per Cosmotron run. The exposure tube was
rotated about its longitudlnal axis at 20 rpm.
The beam was pulsed 25/min. with a pulse dura-
tion of I m sec. giving an instantaneous dose
rate of 14,000 rads/sec, during pulses. The
integrated dose rate was 350 radsJmin, from the
pulsed Cosmotron beam. Dosimetry of the proton
beam has been previously described. (ref. 8, lO).
The doses expressed in this paper are based on:
2.82 x 10 7 p/cm 2 = 1 rad.
- The source of X-rays was a stan-
dard therapy machine operated under the follow-
ing conditions: 250 kVp; 15 mA; 0.5 mm Cu, and
1.0 mm AI added filtration. The dose-rate
measured 60 cm from the target with a Victoreen
condenser R-meter was 118 R/rain. (under condi-
tions of maximum backscatter). In order to com-
pare the absorbed X-ray close with that of protons,
I R was considered equivalent to 0.95 rads.
Eight or ten chicks were exposed at a time in a
rotating lucite chamber 23 cm in diameter and
4 cm thick.
RESULTS
Lethality.,- The time distribution of deaths
fol!owlng exposure to either X-rays or protons Is
given In Table I. In the X-ray group, all _lnl-
mals which died, with one exception, did so in
the intervals 3 - 9 hours or 17 - 30 hours after
exposure. As the dose was increased, a larger
percentage of the animals died in the earlier
(3 - 9 hours) period. Anlmals whlch died fol-
lowing proton exposure did so primarily between
3 and 11 hours &fter exposure, regardless of
dose or 30-hour mortality level. The few anl-
reals which did die in the later period were,
however, in the lower dose groups. A problt
plot of the accumulated 30-hour mortality Is
presented in Figure I. A visual fit of the data
yields a 50% mortality (LD50/30 hours ) dose of
710 rads for both protons and X-rays. The sin-
gle line in Figure I fit both the proton and
X-ray points.
98I9590._ 80_J 70
_ 6o50
k 40
_ 3o
Io
I I I I
600 700 800 900
DOSE (rods)
Finure I. Thlrty-_our_rtallty in th_ Younq
chicken follo_ing proton or X-irradiation.
I
IOOO
661
Lymphatic Organ Involution - Body weights
and lymphatic organ weights obtained five days
after exposure to sublethal doses of either
X-rays or protons are given [n Table II. Organ
weights, as percentage of unirradiated controls
are presented in Figure 2 (thymus), Flgure 3
(bursa), and Figure 4 (spleen). From these
figures, 50_ depression (EDbO) values of approx-
imately 350 rads (thymus), 500 rods (bursa) and
450 rods (spleen) were obtained for protons and
nearly Identical values for X-rays.
80
70
60
5O
_ 30
2O
• TM_MUS
• X°R_Y
0 0 m_OTON
0
o _o
o o
o ¸ %
o
o
o
Io
1(3o
90
80
70
60
i °°
_ _o
2O
I i i _ i
I00 200 300 400 500
DOSE (rods)
Ft_ _.. _hym_cwei_,ts five O=y$after
0
0 0
e X-RAY
0 _OTON
0 0
O0
0 0
0 o 0
O•
m
mOO
= J i _ f
300 40D 500 600
DOSE (_$)
J
7oo
o
o
?DO
DISCUSSION
From Figure I it can readily be seen that
both proton irradiated and X-irradiated chicks
have LDbo/_O_hour values of 710 rods, giving an
R.B.E. for early mortality of 1.0. When high
LET radiations such as fission neutrons are em-
ployed, not only is the R.B.E. considerably above
1 (_.2 for early mortality, ref. 5) but the slope
of the mortality curve is much steeper. For 2.2
GeV protons this is not the case. From Figure I
It can be seen that a single slope is sufficient
to describe both the proton and X-ray mortality
curves. Both the R.B.E. of l.O and the identical
slopes of the mortality curves strongly suggest
that these protons act primarily as low LET radla-
tions. The only difference seen between the
proton and X-ray groups is the tendency for the
proton bombarded animals to die in the earlier
of the two mortality perJ6ds. Although the
reasons for thls are not clear, it is not sugges-
tive of hlgh LET exposures since our own unpub-
lished observations indicate that neutron ex-
posed animals die fairly uniformly throughout
the 3 - 30 hour post-exposure period and do not
exhibit the b/modal concentration of deaths seen
wlth X-rays.
The weights of the thymus, bursa, and spleen
flve days after exposure to various doses are
shown as percentages of control weights in Fig-
ure 2, Figure _, Figure _. These curves reflect
decreases in cell populations due to both scopal
(direct) and abscopal (indirect) radiation
damages and subsequent recovery and repopulation.
Five days after irradiation, the net result of
these processes gives an approxlmately straight
662
I00
90
80
70
60
50
4O
3O
2O
o o
o
o o
o o o
SPLEEN
• X-RAY
0 PROTON
0 0
o o °
D
I0 I I I I I I l
I00 200 300 400 500 600 700
DOSE(rods)
F_ure 4_. Sple;lic w¢iqnts five day_ after
proton or X-irradiation,
line dose-response relationship. The ED50 values
of 350 rad (thymus), 500 rad (bursa) and 450 rad
(spleen) are useful for determining R.B.E. values
but are not indicative of cell sensitivity since
cons i u=, au ,= repalr ,,=0 u_u,,=u, eov=_,o, at
the lower doses. In each case, any line fit
through the proton points could equally fit the
X-ray points indicating that the R.B.E. of 2.2
GeV protons for lymphatic organ involution is
indistinguishable from unity.
These experiments strongly suggest that the
minimally ionizing 2.2 GeV protons act primarily
as low LET radiation, but do not exclude the
possibility that a small component of high LET
is present.
Ueno and Grigoriev (ref. Ill have sug-
gested that a srngle R.B,E. of 0.82 ± 0.04 can
be assigned to all mammalian endpoints tested
for protons between 126 MeV and 730 MeV. This
certainly is not the case with the 2.2 GeV pro-
tons from the Brookhaven Cosmotron. R.B.E.
values from 0.87 to 2.5 have been found under
identical exposure and dosimetric conditions and,
in the case of mouse experiments, the same strain
of animals (ref. 4,8,9,12, and this paper). The
R.B.E. of the 2.2 GeV protons would, therefore,
appear to be dependent upon the particular
biological endpoint under study.
These conclusions have certain practical
implication for space flights. Since the pro-
tons act as low LET radiation, radioprotective
chemicals suitable for man would be effective
against high energy protons( ref. 9, 13). The
effectiveness of low LET radiations is dose-
rate dependent for most endpoints. The estab-
lishment of acceptable dose limits for proton
exposures in space should, therefore, consider
expected dose-rates as well as total doses. In
addition, since the R.B.E. of protons differs
for different endpoints, the tolerance dose
limits must also consider what biological end-
points are critical.
ACKNOWLEDGEMENTS
The authors wish to thank Miss R.F. Straub,
Drs. W. H. Moore, E. P. Cronkite, V. P. Bond, and
the Cosmotron crew.
663
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3. Harris, P. S. and Brennan, J. T.: Report LA-1410, May 1952.
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664


Lymphatic involution and early mortality in the young chicken produced by 2.2 GeV protons

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