102
Rundo®>? observed that the estimated *°°Th content of
tion of °Th during the days immediately foll
and 75% of that of the whole liver. Experiments with
dogs reported by Zilversmit et al.“5) suggest that such
the administered dose in 17 days, and 0.1% i
the whole spleen varied between the wide limits of 8
administration of Thorotrast to two patients (0.
days) can be taken as evidence that a small p
tion of the thorium in Thorotrast mayexist in «:
ble form. Thus, it may well be that the small sk
differences are unlikely to be due to the use of Thorotrast batches of different mean particle sizes. It is
more likely that the explanation can be found in the
different pathological conditions from which these pa-
burden of thorium in Thorotrast patients is d
from such a soluble pool, in which case, like ***
long times after injection,'2) it would be expec
tients suffered, and which were, in part, the reason for
the administration of the Thorotrast. As reported by
have a relatively diffuse distribution.
Rankin et al.,“!® wide variations in the relative uptake
of colloidal material by liver, spleen and bone marrow,
Tissue Distribution of *7P5
Many of the thorium daughter products ar
are observed in patients with liver disease.
The estimate of the thorium content of the whole
marrow-free skeleton obtained in this investigation
was 3.1% of the whole-body burden of **Th. This is
somewhat higher than the values reported by other
workers (Table 37, mean 0.6%). These discrepancies
tributed throughout the body quite differently
the parent nuclide, 7**Th. This is the conseque
various mechanisms which operate to bring abc
lective translocation from one organ to another
the excreta. The phenomenonis probably most m
are not surprising since all the presently available es-
for 21°2Pb and the other daughter products whic
low thoron in the deeay series. Despite the 54
half-life of thoron, its being an inert gas allows :
ciable translocation to occur, even to the exten
timates of skeletal burden are based on extrapolations
from very small, and perhaps nonrepresentative, sam-
ples of bone and bone marrow. A more thorough investigation, embracing manydifferent parts of the skeleton, is definitely required. Concerning its distribution
approximately 10% is exhaled.‘1% 13.14
_212Pb is of little direct significance in the dos)
in bone marrow, a recent autoradiographic study by
Simmons‘2°) has shown that Thorotrast (*2°Th) is de-
of Thorotrast since it emits only low energy 8
rays, and, therefore, contributes very little to th:
energy deposition within the tissues. Neverthelean interesting element to study, for reasons less
posited in rat bone marrow as a “hot line” at the time
of injection and is not translocated further with subsequent bone growth.
The chemical form of the skeletal 7°°Th is of some
interest since it has a bearing on whether the distribu-
tion is likely to be diffuse or ‘hot spot’’, 1.e. concen-
trated in colloidal particles. The observation by Hursh
and his colleagues’ of a small but significant excreTABLE 38.
ficial than that its activity happens to be r
measurable. In most of the tissues its biological
life is considerably longer than its physical he
of 10.6 hr.“® Therefore, there are good groun
expecting that 7!°Pb can be used to estimate the
ities of its dosimetrically important precursors,
Tissurp DistrinutTion oF #?2Pb™
Animal
Ageof
Code
Liver
Spleen
Kidney
Rat
35d
38d
4ld
72
73
67
160
100
100
111
200
185
19
32
237
TH3
100
228
228
18m
TH2
22m
12m
TH4
100
100
120
—
311
THS5
100
241
Dog
21d
78
100
17
Man
48d
85
100
59
8
100
144
2
|
‘) Concentration of 2“Pb/g of tissue as “% of liver concentration.
) Kidney medulla.
(e} Kidney cortex.
Cortical
Redbone
Bloo
400
22m
Mean values
Lung
:
202
8°) bog
9
BGC)
=|
35
8
30
2
85
9
30
2