Plutonium Biokinetics in Human Body A. Luciani - Kit-Bibliothek - FZK

modified version (ICRP67-a) (i.e. without the transfer of activity from ST0 soft tissue
compartment to urinary bladder). The improvement of the long term urinary excretion of
Plutonium by adopting the modification of the skeleton from Polig’s studies with age
depending remodelling rates is shown in Table 3.1.8. The values of the F target function
based on the previous models are also presented.
Table 3.1.8 Values of the F target function for the long term (t > 200 d) urinary excretion
using original and modified versions of ICRP 67 model.
Model
106
F value
For t > 200 d
ICRP67 14
ICRP67-a 394
ICRP67-a-Polig 56
ICRP67-a-Polig-ST0 56
Model-a 53
Model-b 5
As discussed on the basis of Figure 3.1.8, for the previous finale stage of revisions it
was not necessary to repeat the optimization of the transfer rates of the urinary pathway that
provided a good agreement with the reference data set at short time. Introducing new liver
transfer rates and age dependent skeletal remodelling rates had no significant influence on the
urinary excretion at early times and Model-b yielded practically the same values than Modela.
The urinary excretion in Figure 3.1.16 was calculated for a subject who is 45 years old at
the time of injection, the age of subject HP-6 in the reference data set for whom we have data
at long times. With the current assumptions of Model-b the estimated urinary excretion of
Plutonium is now higher than the predictions of Model-a. From day 200 to around 10,000 the
model shows sufficient agreement with Khokhryakov’s excretion curve. The deviations never
exceed 30%. At day 10,000 Model-b estimates a urine excretion of 0.0012%/d -1, very close to
the experimental value. Therefore the modifications applied to the ICRP 67 model seem to
compensate very well for the underestimation of urinary excretion caused by removing the
connection between soft tissue and urinary bladder (ICRP67-a). The Model-b prediction for
the skeleton-liver partitioning was also calculated (0.615) and is in good agreement with the
published values [158, 159, 160, 161].
Model-b was derived with the primary goal to achieve the best estimates of urinary
excretion, but estimates for fecal excretion and plutonium activity in blood were also taken
into account in the optimization procedures. The calculated excretion rate in feces and the
percentage of Plutonium in blood are presented in Figure 3.1.17 and Figure 3.1.18,
respectively, together with the estimates from ICRP 67, its modified versions and the
reference data set. The fecal excretion of Model-b is closer to the experimental data than
ICRP 67. Model-b underestimates the measurements by less than 40 %, while ICRP 67 by 80
% or more. Furthermore the fecal excretion of the model has almost the same trend as the
experimental data, even at short time (up to 7 days post injection) when it is characterized by
an initial increase followed by a sharp decrease. The overall good performance of Model-b
with regard to fecal excretion is confirmed by the values of the F target function calculated on