Biomedical Engineering Reference
In-Depth Information
and
H
b
(50) = 1.6 × 10
-10
U
b
SEE(
b
←
b
)
(16.61)
= 1.6 × 10
-10
× 7.5 × 10
3
× 1.9 × 10
-3
= 2.3 × 10
-9
Sv.
(16.62)
The last number represents the committed equivalent dose in organ
b
that is de-
livered by radionuclides in
b
after they have left
a
. Since organ
b
is also irradiated
as a part of the whole body by radionuclides in
a
, the total committed equivalent
dose in
b
is the sum of (16.62) and (16.60). The later contribution, however, is neg-
ligible. The committed effective dose [Eq. (16.42)] is the sum of (16.60) and (16.62),
weighted by the given factor
w
T
=
10
-11
+0.05
10
-9
0.05. Thus,
E
(50)
=
1.2
×
×
2.3
×
=
1.3 × 10
-10
Sv.
In ICRP Publication 30, the committed dose equivalent per unit intake, the an-
nual limit on intake (ALI), and the derived air concentration (DAC) all refer to the
intake of a specified radionuclide alone. If the radionuclide decays into radioactive
daughters, then these are also included in the calculations of committed equivalent
dose. The computations include either specific metabolic data for the daughters or
the assumption that they follow the transport of the parent. Values of the number
of transformations
U
S
in source organs S for a radionuclide are computed together
with values
U
S
,
U
S
, and so forth, for the daughter radionuclides that build up in
the body during the 50 y following intake of the parent.
With the adoption of ICRP Publication 60, the Commission instituted the use
of the committed effective dose in place of the committed effective dose equiva-
lent. These are fundamentally different quantities. The ICRP also defined the ALI
with reference to a committed effective dose of 20 mSv in place of a committed
effective dose equivalent of 50 mSv. In addition, a new set of tissue weighting fac-
tors was adopted. These changes and the 1994 ICRP-66 revision of the lung model
necessitated new calculations of the relationships between intakes and resulting
committed organ equivalent doses and individual committed effective doses. The
new information is presented in the 1995 ICRP Publication 68,
Dose Coefficients for
Intakes of Radionuclides by Workers
. The complete revision of the ICRP-30 protocols,
which is in progress, will take into account the newer anatomical and physiological
data (ICRP-89) and continuing development of biokinetic models.
Dose coefficient
is defined in ICRP-68 as “the committed tissue equivalent dose per unit acute in-
take
h
T
(
)
, where
τ
is the
time period in years over which the dose is calculated (e.g.,
e
(50)
).” The dose co-
efficient has the units Sv Bq
-1
. The quantity is also referred to as a
dose conversion
factor
(DCF). The acute intake of an amount of activity (by inhalation or ingestion)
multiplied by the DCF gives the committed effective dose. For the 50-y committed
effective dose of 20 mSv, the annual limit on intake is thus given in terms of the
dose coefficient
e
(50) by
τ
)
or committed effective dose per unit acute intake
e
(
τ
0.020 Sv
e
(50) SvBq
-1
=
0.020
e
(50)
Bq.
ALI
=
(16.63)
