Biomedical Engineering Reference
In-Depth Information
Table 14.2
Tissue Weighting Factors,
w
T
Tissue or Organ
w
T
Gonads
0.20
Bone marrow (red)
0.12
Colon
0.12
Lung
0.12
Stomach
0.12
Bladder
0.05
Breast
0.05
Liver
0.05
Esophagus
0.05
Thyroid
0.05
Skin
0.01
Bone surface
0.01
Remainder
*
0.05
* Note: The data refer to a reference population of equal
numbers of both sexes and a wide range of ages. In the
definition of effective dose, they apply to workers, to the whole
population, and to either sex. The
w
T
are based on rounded
values of the organ's contribution to the total detriment.
The risk for all stochastic effects for an irradiated individual is represented by
the effective dose,
E
, defined as the sum of the weighted equivalent doses over all
tissues:
E
=
T
w
T
H
T
.
(14.4)
Like
H
T
,
E
is expressed in Sv. The risk for all stochastic effects is dependent only on
the value of the effective dose, whether or not the body is irradiated uniformly. In
the case of uniform, whole-body irradiation,
H
T
isthesamethroughoutthebody.
Then, since the tissue weighting factors sum to unity,
H
T
T
E
=
w
T
H
T
=
w
T
=
H
T
,
(14.5)
T
the value of the equivalent dose everywhere. The effective dose replaces the earlier
effective dose equivalent. The latter quantity was defined the same way as
E
in
Eq. (14.4), with
H
T
being the organ or tissue dose equivalent.
It should be understood that the procedures embodied in Eq. (14.4) have been set
up for use in radiological protection. As the note to Table 14.2 specifies, the values
of
w
T
are simplified and rounded for a reference population of equal numbers of
males and females over a wide range of ages. As stated in NCRP Report No. 116
(p. 22), they “should not be used to obtain specific estimates of potential health
effects for a given individual.”
