Strontium-90
of the generic method described by Adams(1981)
and by Leggettet al. (1984).
Several models have been developed over
the years to estimate the cycling and retention
Thecalculation for photon emissions is more
complex because the entire energy of the photon
of 99Sr in the body as a function of age to
is not absorbed in the source organ. As the body
calculate age-dependent dose conversion factors
(Kulp and Schulert, 1962; Rivera, 1967; Bennett,
and organ size become smaller,.a larger portion
of the energy escapes the source organ and the
relative position of the organs is significant.
Consequently, if the charged-particle-emission
concept is used for making age-dependent
adjustments for the total energy released per
1973, 1977, 1978; Klusek, 1979; Papworth and
Vennart, 1973; Leggett et al., 1982).
We have
previously used both the model developed at
EML (Rivera, 1967; Bennett, 1973, 1977, 1978;
Klusek, 1979) and that of Papworth and Vennart
transformation for a radionuclide like 137Cs
that has both charged-particle and photon
(1973).
The two models give very similar
results, with the biggest difference in results
occurring for persons between ages 5 and 15 y.
Both models are empirical models based on
emissions, the actual dose for infants and
children will be overestimated. However, this
procedure can be used for 137Cs_ for a quick,
measurements
of
29Sr in the diet and
conservative approachto the relative dose from
137Cs asa function ofthe ageat intake.
Leggett et al. (1984) and Cristy and
corresponding measurements of 9°Sr in autopsy
that account for changes in deposition of photon
solution-fitting of the observed data.
No
Vennart's model does include -the
two
bone samples. The retentions and turnoverrates
and discrimination factors in the models are
determined by regression analysis or equation
Ekerman (1987a to 1987g) have calculated agedependent energy deposition factors (S factors)
energy as a function of size (i.e., age).
The
particular correlation is made with bone
compartments, as outlined by the [CRP (1972,
1979), in the EML model, but Papworth and
_ Tesults are based on Monte Carlo calculations in
various sizes of computer-generated phantoms;
the S factors are presented for newborn, 1-y-old,
5-y-old, 10-y-old, 15-y-old males, and adult
females and adult males. Values for other ages
are obtained bylinear interpolation.
compartments of compact and cancellous bone.
A recent model developed by Leggett etal.
(1982) is based on the structure and function of
We have combined the age-dependent
modifications to the ICRP model for charged-
particle emissions
bone compartments as generally outlined in the
ICRP model (1972, 1979). The bone is assumed to
be composed of a structural componentassociated
with bone volume, which includes the compact
cortical bone, a large portion of the cancellous
for the beta-particle
emissions (E = 0.51 meV) from 137Cs and the
methodsof Leggett et al. (1984) and Cristy and
Ekerman (1987a to 1987g) for the photon
(trabecular) bone, and a metabolic component
emission (E = 0.66 meV) associated with 137Cs
associated with bone surfaces. In effect, three
decay to generate the final age-dependent dose
conversion factors.
compartments are then identified, two within
the bone volumeandonewithin the bonesurface.
The biological half-life of 137Cs_ is
The bone volumeis associated with mechanical
structure and integrity of the bone, and the bone
surface is involved with the metabolic
determined as a function of mass(i.e., age) by
the methods described in the "Retention"
section.
regulation of extracellular calcium. Much use is
The age-dependent energy deposition
factors and biological half-life are combined to
madeof general data about age-dependent bone
formation within these compartments and,
consequently, this model is not as dependent on
adjust the ICRP dosimetry methods for !37Cs to
an
CC
an age-dependent model.
radionuclide-specific data as the other models.
16