Internal Dosimetry and Radiation Protection - Atoms, Radiation, and-Radiation Protection - page 509

Fig. 16.3 Mathematical model usually employed for transfer of
a radionuclide from the body fluids (compartment a) to various
organs and tissues and its subsequent excretion. [From data in
Annals of the ICRP , Vol. 2, No. 3/4, ICRP Publ. 30, Part I,
International Commission on Radiological Protection, Sutton,
England (1979).]

Compartment a is linked to other compartments, b , c , ... , i , ... , representing var-
ious tissues and organs in the body, from which the nuclide can later be excreted.
A radionuclide undergoes metabolic clearance from these compartments, as well
as radioactive decay. Unless otherwise specified, the metabolic half-life used for the
transfer compartment a is 0.25 day. Radioactive transformations that occur in this
compartment are assumed to be distributed uniformly in the 70-kg reference man.
For simplicity, excretion in the model does not involve transport through compart-
ment a , although, realistically, the body fluids are involved. For this reason, the
calculated amount of a radionuclide in compartment a at some time after inhala-
tion or ingestion cannot be used as an estimate of the amount of the radionuclide
in the body fluids at that time.
After a radionuclide leaves the transfer compartment a , the ICRP metabolic
model continues to trace its movement through the various tissues and organs
in the body, represented by compartments b , c ,

... ,whichmaybeintercon-
nected. Explicit metabolic parameters are given for each radionuclide, its pertinent
chemical forms, and all organs and tissues. The activity of the radionuclide in any
organ can be calculated explicitly as a function of time after intake. The equivalent-
dose rate in the organ from decay of the radionuclide it contains can be computed

... , i ,