wT
tote
saan bee a! siblebe Mial hats Sates einen st «
110
of the *!°Pb and ?!*Bi atoms observed in the RES are
not bound within the particles. The high activities of
both these isotopes can be explained by the fact that
*8Ra/*3"Th ratios come out somewhat higher
those imphed by the figures of Tables 42 and 43.
swnably because of the aggregation of Thorotrast
ticles that occurs at long times after administrati
For individual tissues at long times after Thoro
administration, the steady state activity ratio:
served by the present authors and those reported
viously by other workers, are summarized in Tab:
On the basis of these data a collection of current *
their biological half-lives within the RES are much
longer than their physical half-lives. 1
Best Estimates of the Distribution of Activities
throughout the Human Body and the Consequent
Radiation Dose-Rates in Long-Term Thorotrast
Patients.
estimates” (in the present authors’ opinion) o
There is unfortunately no completely objective way
steady state activity ratios has been assembled i
ble 50. In cases where no human data were ava!
for this table, the best estimates were derived frat
results of the animal experiments reported abov:
data are quoted for the ratios ??°Em/**4Ra. How
from thoron breath analyses and calculations inve
the circulation time of the blood, it is possible to
to combine the data reported here with those of other
workers to obtain the current “best estimates” of the
distribution of Thorotrast activities throughout the hu-
man body. Different investigators undoubtedly tend to
attach different weighting factors to all the evidence
that is available.
For the whole body, the most reliable estimates of
the steady state activity ratios of the various thorium
daughter products are probably derived from excretion
measurements. The relations between percent excreted
per dayand activity ratio in the whole body are of the
form shown for four of the thorium-series radionu-
clides in Figure 87. Steadystate activity ratios calcu-
lated on this basis for the whole body are summarized
in Table 49. It is to be noted in particular that the
100
a rough estimate of the proportion of thoron :
generated within the major Thorotrast deposits 1
RES which escape into the general circul.
Hursh®® calculated 16%, and Grillmaier et
concluded that it might even be as high as 20%
tissues other than the RES, the expected thorona
ties are more difficult to predict. From Stover’s
on #2Pb metabolism ®” there is some evidence
TTT TTT]
Ty
T
y
TT
TTit
ACTIVITY RATIO (%)
212Ph /232Th
80
22474 /232 TH
60
40-
228TH /232 Th
2228p, / 2327p
20;+o
0.01
to
f
i
etl
0. |
dof
py
L
1.0
l
risa)
10.0
Jet
i
ttl
100.0
% EXCRETED PER DAY {as fraction of total body content)
Fra, 87,—Relation between steady state activity ratios in the whole body and the excretion rates of four thorium serie+
products.
TABLE 50.
AtctHors’ “Best Estimates” or Steapy Stare Activiry Rarros 1y Loxeg-Team THorotrast PAtTiEeN”
Organ
Liver
28Ra 22@Th
|
28AC/8Ra
0.5
1.00
0.2
1.4)
Spleen
0.5
Trabecular bone
1.3%)
(1.0)
0.2
0.5
(1.0)
(£.0)
Kidney
Red bone marrow
Lung
1,00
28Th/#8Ra
|
|
|
24Ra /28Th
wPh /PARa
21273; /22Pb
0.9
0.7
0.5
0.7
1.43
0,9)
4,7)
1.90)
9.9
1.1
1.1
1.0
0.7
1.7
0.6
~1
0.5
0.9)
=1
~18
0.7
1.0
(1)
(1)
Source of
,
|
Table 4s
"Fable 48
Table 44
Tables 4°
Tables 4:
Table 46
(a) Except where indicated, the quoted values are based on measurements of tissues from actual long-term Thorotrast p
(6) Based on data obtained from experimental animals.
‘c) Values much greater than one are observed in short-term animal experiments (Table 45).
@) Assumed value in absence of actual measurement.