July 24, 1996
EPA-SAB-RAC-COM-96-003
Ms. Carol M Browner
Administrator
U.S. Environmental Protection Agency
401 M Street, S. W.
Washington, DC 20460
RE: Radiation Advisory Committee Commentary on the Scientific
Basis for Apportioning Risk Among the ICRP Publication 66
Regions of the Respiratory Tract
Dear Ms. Browner:
This Commentary was developed by the Radiation Advisory Committee (RAC)
of the Science Advisory Board (SAB) in response to a request from the Office of
Radiation and Indoor Air (ORIA) within the Office of Air and Radiation (OAR). At a
RAC public meeting on May 25, 1995 Dr. Jerome Puskin and Dr. Neal Nelson from
the Office of Indoor Air briefed the RAC on their concerns about the scientific basis
for apportioning risk among regions of the respiratory tract in the new ICRP Human
Respiratory Tract Model for Radiological Protection, published in International
Commission on Radiological Protection (ICRP) Publication 66 (ICRP, 1994). ORIA
is considering using the new ICRP model in Federal Guidance Report Number 13.
Subsequently the RAC discussed this topic at public meetings on January 25, 1996,
April 30, 1996 and May 21-22, 1996.
This Commentary concludes that the use of default values to apportion the
tissue weighting factor for lungs in calculating effective doses from inhaled radionu-
clides, recommended by the ICRP in the absence of published data supporting
specific values, would not have a major impact on radiation protection. A small
measure of conservatism would be added to dose calculations for certain insoluble
radionuclides. The RAC recommends that EPA use the model as adopted by the
ICRP and NCRP and that it also undertake an effort to provide, for consideration by
the ICRP and NCRP, a more scientifically acceptable basis for apportioning the
tissue weighting factor for the lungs. Such an effort could strengthen the credibility
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of the ICRP model among those familiar with respiratory tract pathology, although
not necessarily improve its usefulness for radiation protection. In the meantime the
use of the default values would be an appropriate topic for EPA to consider in
addressing the uncertainties of radionuclide dose calculations such as are required
for clean-up of sites contaminated with radionuclides. However, uncertainties in
other aspects of the model, including morphometry (dimensions of the anatomical
and histological features of the respiratory tract), quantitative and qualitative
deposition of inhaled particles and the rates of clearance of inhaled material from the
lungs, likely have a greater impact on the results obtained with the ICRP model and
with any other model developed with the existing data base than the default values
for apportioning the tissue weighting factor.
BACKGROUND
The International Commission on Radiological Protection (ICRP) and the
National Council on Radiation Protection and Measurements (NCRP) adopted the
concept of "effective dose (£)" which is designed to predict the same probability of
the occurrence of cancer and genetic effects whether the whole body is uniformly
irradiated or non-uniformly irradiated. Uniform exposures can occur from external x-
rays, gamma-rays and neutrons and also from soluble radionuclides uniformly
distributed throughout the body. Non-uniform exposures usually occur from non-
uniform distribution of internally deposited radionuclides and by partial body
irradiation from external sources of x-rays, gamma rays and neutrons. Because
organs and tissues of the body are not all equally sensitive, the calculated doses
received by individual organs and tissues must be adjusted to account for these
differences to obtain expressions of effective dose. Drawing from studies of health
effects observed in populations exposed to relatively uniform irradiation, such as the
Japanese atomic bomb survivors, the ICRP and NCRP developed tissue weighting
factors (WT) to be applied to the doses calculated for each tissue and organ in the
body. For gonads WT is 0.20; for red bone marrow, colon, lung and stomach it is
0.12; for bladder, breast, liver, esophagus and thyroid it is 0.05; and for skin and
bone surface it is 0.01, for a total of 0.95. An additional WT of 0.05 is applied to all
remainder tissues. For each tissue the calculated equivalent dose (/-/T), product of
the averaged absorbed dose and the radiation weighting factor (WR) for the radiation
type, is multiplied by the appropriate tissue weighting factor (WT ) to obtain the
weighted equivalent dose. The effective dose is the sum of these weighted equiva-
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lent doses for all tissues and organs in the body1 (ICRP, 1991; ICRP, 1995; NCRP,
1993).
Earlier dosimetric models for the respiratory tract (Taylor, 1984; ICRP, 1960;
TGLD, 1966; ICRP, 1979) ignored the extrathoracic tissues and also the differences
in the relative sensitivity of the numerous tissues within the lungs, simply averaging
the radiation dose over the total mass of the lungs and associated lymph nodes, with
the assumption that the radionuclide contents of these tissues were uniformly
distributed2. In ICRP Publication 30 (ICRP, 1979) this calculated averaged dose
was multiplied by the tissue weighting factor for lungs of 0.12 and added to similar
doses calculated for other tissues in the body to give the effective dose equivalent,
later renamed the effective dose (ICRP, 1991). This approach is especially subject
to criticism because inhaled radionuclides are rarely if ever deposited and retained
uniformly throughout all lung tissues. Thus, the dose may be very non-uniform
among the several different lung tissues which may vary considerably in their
sensitivity to radiation. For example, highly insoluble inhaled radionuclides with long
half-lives tend to accumulate in the lymphatic tissues, which are relatively insensitive
to radiation. The very high doses these tissues can accumulate have little bearing
on the potential for health effects to occur. On the other hand, doses from radionu-
clides with very short retention times in the lungs, because of rapid decay or fast
absorption into the blood, tend to be higher in the more sensitive tissues of the
airways.
The new ICRP model (ICRP, 1994) was designed to accommodate the
potentially large differences in the doses received and the differences in radiation
sensitivities of the various tissues comprising the respiratory tract as well as being
compatible with the ICRP dosimetry system (ICRP, 1991). The model provides for
the calculation of quantities of inhaled material deposited in the several tissues and
1 Because radionuclides may remain in body tissues and organs for years after an intake, it is useful to
calculate the total radiation doses received during the residence time of radionuclides in the body. This
committed weighted equivalent dose (/-/T(T)) is the time integral of the equivalent dose rate in a particular tissue
or organ that will be received by an individual following intake of radioactive material into the body where T is the
integration time in years following intake, 50 years for adults and from intake to age 70 years for children. The
sum of the committed weighted equivalent doses for all tissues in the body is the committed effective dose (E(i))
(ICRP, 1995).
2 Both the ICRP and the NCRP have recognized the non-uniform irradiation of the lungs following inhalation of
radon and its decay products. The ICRP proposed assigning half of the tissue weighting factor of 0.12 to the
basal cell layer of the tracheo-bronchial region and half to the pulmonary region (ICRP, 1981). The NCRP
calculated doses to the bronchial epithelium as well as to the whole lung (NCRP, 1987).
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the residence times in these tissues. Using the mass of each tissue the radiation
dose can be calculated.3 As noted above, the ICRP (ICRP, 1991) assigned a tissue
weighting factor, WT, of 0.12 to the lungs, the tissues within the thorax. In the new
model (ICRP, 1994) the WT is to be apportioned among the tissues of the lungs in
relation to their radiation sensitivity, in conformity with the ICRP system. The
apportionment of the 0.12 tissue weighting factor among the various tissues of the
lungs is the issue addressed by this Commentary.4 To achieve this apportionment
correctly, it is necessary to know the relative sensitivity of the different lung tissues
to the induction of cancer by radiation or to know the relative probability of cancers
arising in the various lung tissues after the total lungs receive a uniform dose of
radiation. In estimating radiogenic cancer risks, the EPA (EPA, 1994) assigned 80%
of the lung weighting factor to the tracheo-bronchial region and 20% to the pulmo-
nary region. However, the basis for this apportionment of the weighting factor was
not given. After a thorough review of all the available information, the ICRP deter-
mined that there are no data from either animal experiments or human epidemiology
studies to answer this question unequivocally.
Autopsies only provide information about the location of cancer tissues at the
time of death, which may or may not have any relation to the site of origin. Lung
cancers have been labeled as to cell type which may suggest the cell of origin and
possibly give a clue as to the tissue of origin. However, the ICRP (ICRP, 1994)
determined that such data from experimental animals and from humans in which
lungs received uniform exposures to radiation, are not of sufficient quality and
quantity to derive estimates of relative sensitivity suitable for apportioning the 0.12
weighting factor among the several regions of the lungs.5
3 The tissues identified by the ICRP (ICRP, 1994) for dose calculations are the anterior nose and the posterior
nasal passages including the larynx, pharynx and mouth in the extrathoracic part of the respiratory tract. The
tissues identified in the thorax are the tracheal and bronchial epithelium (the latter being divided into the mass of
basal cells and the mass of secretory cells, specified separately because these appear to be the radiation
sensitive cells), designated the Bronchial Region; the bronchiolar epithelium and respiratory bronchioles,
designated the Bronchiolar Region; and the alveolar ducts and sacs and the interstitial connective tissues,
designated the Alveolar-interstitial Region. Lymph nodes associated with the respiratory tract were also identified
for dose calculations.
4 According to the ICRP (ICRP, 1994) dose calculation scheme, the extrathoracic tissues were included in a
category of "other tissues" for assignment of a tissue weighting factor. The extrathoracic tissues are not among
the more radiation sensitive tissues in the body and the assignment of weighting factors to these tissues was not
identified as an issue to be addressed by this Commentary.
5 In the studies in which lung cancers appeared to be disproportionally distributed among lung regions, the
radiation exposures were non-uniform and the regions where cancers were observed generally received the
highest doses. Also it is uncertain whether tumor types observed in experimental animals will occur in humans.
As a result, definitive conclusions about differences in radiation sensitivity could not be drawn.
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Because information from radiation studies was lacking, the ICRP (ICRP,
1994) considered other approaches for apportioning the tissue weighting factor for
lungs. For example, in humans not exposed to radiation other than that from natural
background, it can be estimated from autopsy information about location of lung
tumors and tumor cell types that 60 to 80% of tumors are of bronchial origin, 15 to
30% are of bronchiolar origin and 5 to 10% are of alveolar origin. A complicating
factor, though, is cigarette smoking, which is thought to increase the fraction of
tumors that originate in the bronchial region. Therefore, for non-smoking popula-
tions a distribution of 60% bronchial, 30% bronchiolar and 10% alveolar may be
reasonable. However, use of this relative risk approach to apportion the 0.12 tissue
weighting factor for lungs requires the assumption that exposure to radiation results
in all the naturally occurring lung tumors being increased proportionally. Although
there is evidence that radiation induces, in certain other organs and tissues, some of
the same kinds of cancers that occur naturally, and for some cancers a relative risk
model may be appropriate, application to the different tissues in the lungs did not
appear justified to the ICRP. Therefore, as a default, until suitable information
becomes available, the ICRP apportioned the 0.12 tissue weighting factor as follows:
33% to the bronchial tissues, equally divided between the basal and secretory cell
masses; 33% to the bronchiolar tissues; and 33% to the alveolar-interstitial tissues.
It may be somewhat surprising that the extensive research on radiation-
induced lung cancer in experimental animals and in human populations such as
underground miners and the Japanese atomic bomb survivors is inadequate to
specify the relative radiation sensitivity of the different tissues of the lungs. There is
a general belief among researchers in this field of study that in animals and humans
exposed to radiation from inhaled radionuclides, more cancers appear in the
bronchial region than in other regions except in experimental animals where concen-
trations of long-lived alpha-emitters induced cancers in the bronchiolar-alveolar
tissues.6 This general observation of a greater frequency of lung cancer in the
bronchi than in other regions of the lungs has promoted the idea that the bronchial
epithelium is very likely the most radiation sensitive tissue and should be assigned a
larger proportion than 33% of the tissue weighting factor for lungs. However, the
ICRP (ICRP, 1994) determined that, until the relative sensitivities of lung tissues to
6 Cancers in humans exposed to long-lived alpha-emitters such as plutonium have not been observed in the
United States or elsewhere with the possible exception of the former Soviet Union. Recent unpublished
information from Russia describes an increased incidence of lung cancer among plutonium workers, but details
including tumor type and tissues of origin are not yet available.
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radiation are documented in the scientific literature, the default apportionment values
should be used.
While the default values may be objectionable to those who believe the
bronchial, bronchiolar and alveolar-interstitial tissues of the lungs are not equally
radiation sensitive, the more important radiation protection question is the sensitivity
of the dose estimates obtained with the new model to the selection of apportionment
values used in the dose calculations. This question is explored in the following
examples of lung doses and effective doses calculated for several radionuclides
using the default values and also calculated with two sets of apportionment values,
Case 1 and Case 2, derived from information about the frequency of naturally
occurring, non-radiation-induced, lung cancers. In these calculations the apportion-
ment of the 0.12 weighting factor for lung among the regions of the lungs is as
follows:
a) Default: 33% to the bronchial epithelium divided equally (16.67%
each) between basal and secretory cell tissues, 33% to the bronchiolar
tissues and 33% to the alveolar-interstitial tissues (first column).
b) Case 1: 60% to the bronchial tissues divided equally (30% each)
between basal and secretory cell tissues, 30% to the bronchiolar
tissues and 10% to the alveolar-interstitial tissues (second column);
and
c) Case 2: 80% to the bronchial tissues divided equally (40% each)
between basal and secretory cell tissues, 15% to the bronchiolar
tissues and 5% to the aveolar-interstitial tissues (third column). (This
case is most similar to the EPA's apportioning 80% of the lung weight-
ing factor to the tracheo-bronchial region and 20% to the pulmonary
region (EPA, 1994) in calculating doses for estimating radiogenic
cancer risks.)
In all cases a value of 0.1% was assigned to lymph nodes. The doses are
calculated for a standard worker: 31.3% of the time sitting and 68.7% doing light
exercise. The software, LUDEP 1.1 (Personal Computer Program for Calculating
Internal Doses Using the New ICRP Respiratory Tract Model) (NRPB, 1994), was
used to calculate both committed weighted equivalent doses for lungs and commit-
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ted effective doses7. The lung doses include contributions from radiation emitted
from radionuclides deposited in the lungs and translocated to other tissues and
organs in the body. These doses are not significant for alpha emitters.
Highly insoluble compounds of relatively long-lived radionuclides of elements
such as plutonium and strontium are only slowly absorbed into the blood from the
respiratory tract. The calculated doses given in Table 1 for 239Pu and for 90Sr show
that both the total lung doses (committed weighted equivalent doses) and the
effective doses (committed effective doses) are greatest (up to more than two times
for 0.02 and 0.1 um AMAD (Activity Median Aerodynamic Diameter) 239Pu aerosols)
when the default values for apportioning the tissue weighting factor are used,
Column 1. For more soluble 1 um AMAD aerosols absorbed from the lungs at a
moderate rate, 238Pu and 210Po (alpha emitters), the calculated lung doses are
slightly less when the default values are used, but the effective doses are about the
same for all cases. However, for smaller particle size 210Po aerosols, 0.1 um AMAD,
the default values lead to somewhat higher calculated lung and effective doses. The
calculated lung and effective doses for soluble compounds of such radionuclides as
137Cs and 131I (beta-gamma emitters) that are rapidly translocated from the lungs to
other tissues in the body are not sensitive to the choice of factors used for apportion-
ing the risk among the different regions of the lungs.
It is debatable whether even the largest differences, slightly more than a
factor of two in these example calculations, would have any significant impact on
limiting exposures or estimating risks from exposures to air-borne radionuclides.
Although these examples are limited in number, they include the radionuclides likely
to be among the most sensitive to how the tissue weighting factor is apportioned,
i.e., alpha-emitting, long-lived insoluble radionuclides which are retained in the
lungs sufficiently long to result in the lung dose being a substantial contribution to
the effective dose. Radon and its decay products are not included in these example
calculations because the ICRP (ICRP, 1993) advises using risk estimates directly
from epidemiology data rather than calculating lung and effective doses.
CONCLUSION & RECOMMENDATIONS
7 This version of LUDEP, LUDEP 1.1, uses ICRP Publication 30 biokinetic models (ICRP, 1979). LUDEP
2.0, available in June 1996, uses updated biokinetic models from ICRP Publications 56 (ICRP, 1989), 67 (ICRP,
1993a) and 69 (ICRP, 1995). Inhalation dose coefficients in recent ICRP Publications 68 (ICRP, 1994a) and 71
(ICRP, 1995a) are based on the newer biokinetic models and, thus, differ slightly from the values calculated in
Table 1 in this commentary.
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The use of default values to apportion the tissue weighting factor for lungs in
calculating effective doses from inhaled radionuclides would not appear to have a
major impact on radiation protection. For certain insoluble radionuclides, but
unlikely for soluble radionuclides, the use of the default values could add a small
measure of conservatism to dose calculations. Neither the ICRP nor the NCRP
believes the use of the default values poses a barrier to the adoption of the new
dosimetric model for the human respiratory tract. When more acceptable values for
apportioning the tissue weighting factor for lungs are obtained, the default values
can be readily replaced. In the interim the RAC recommends the EPA use the new
dosimetric model for the human respiratory tract as adopted by the ICRP and NCRP
to calculate lung doses for inhaled radionuclides such as in the preparation of
Federal Guidance Number 13 and in clean-up of sites contaminated with radionu-
clides.
However, the need to use default values indicates a lack of scientific informa-
tion that, if corrected, could improve the credibility of the ICRP model among some of
those familiar with respiratory tract pathology. The use of default values does not
appear to weaken the usefulness of the model for radiation protection. For this
purpose then, the RAC recommends EPA continue an effort to provide for adoption
by the ICRP and NCRP a more scientifically acceptable basis for apportioning the
tissue weighting factor for lungs. This effort could involve reexamining the literature
for data on the relative radiation sensitivity of the several regions of the lungs
including more recent results of epidemiology studies and animal experiments as
well as studies that might identify the frequency distribution of radiation sensitive
cells in the various regions of the lungs. Lacking success identifying scientifically
credible published information that would justify replacement of the default values,
the EPA might consider supporting the necessary research to do so. An EPA effort
that resulted in a scheme for apportioning the lung tissue weighting factor that could
be adopted by the ICRP and NCRP would be welcomed by the radiation protection
community. The adoption of values by the EPA independent of the ICRP and NCRP
would cause confusion in the calculation of effective doses in the U.S.
We trust this Commentary will offer some insights on the issues associated
with apportioning the tissue weighting factor for the lungs in the new ICRP Dosimet-
ric Model for the Human Respiratory Tract and on the opportunity for the EPA to
contribute to improving the scientific basis for that aspect of the model.
8
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Sincerely,
Dr-3ames E. Watson, Jr., Chair Dr. Genevieve M. Matanoski, Chair
Radiation Advisory Committee Executive Committee
Science Advisory Board Science Advisory Board
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APPENDIX A
TABLE 1: THE SENSITIVITY OF TOTAL LUNG AND EFFECTIVE DOSE CALCU-
LATIONS TO THE CHOICE OF VALUES USED TO APPORTION RISK AMONG THE
REGIONS OF THE LUNGS (Refer to Footnote to Table 1, p. A-4)
A. mPu (moderate rate of absorption). 1 |im AMAD. T^ = 87.7 years
(an alpha emitter)
Regional Lung Dose (Sv/Bq)
Lung Region Default
Bronchial, basal cells 1.02 E-07
Bronchial, secretory cells 1.23 E-06
Bronchiolar 1.69 E-06
Alveolar-iterstitial 6.93 E-07
Lymph nodes 3.84 E-10
Total Lung Dose (Sv/Bq) 3.72 E-06
Effective Dose (Sv/Bq) 4.83 E-05
Case 1
1.84 E-07
2.21 E-06
1.52 E-06
2.08 E-07
3.84E-10
4.13 E-06
4.87 E-05
Case 2
2.45 E-07
2.95 E-06
7.62 E-07
1.04 E-07
3.84E-10
4.06 E-06
4.86 E-05
B. 239Pu (slow rate of absorption). 0.02 urn AMAD. T1/2 = 24.065 years
(an alpha emitter)
Regional Lung Dose (Sv/Bq)
Lung Region
Bronchial, basal cells
Bronchial, secretory cells
Bronchiolar
Alveolar-interstitial
Lymph nodes
Total Lung Dose (Sv/Bq) 5.34 E-05
Effective Dose (Sv/Bq) 8.46 E-05
Default
1.98 E-07
3.43 E-06
2.45 E-05
2.48 E-05
4.96 E-07
Case 1
3. 56 E-07
6. 17 E-06
2.21 E-05
7.44 E-06
4.96 E-07
Case 2
4.75 E-07
8. 22 E-06
1.11 E-05
3. 72 E-06
4.96 E-07
3.66 E-05
6.77 E-05
2.40 E-05
5.51 E-05
C. 239Pu (slow rate of absorption). 0.1 um AMAD. T1/2 = 24.065 years
(an alpha emitter)
Regional Lung Dose (Sv/Bq)
Lung Region Default
Bronchial, basal cells 6.48 E-08
Bronchial, secretory cells 1.18 E-06
Bronchiolar 9.48 E-06
Alveolar-interstitial 1.51 E-05
Lymph nodes 2.66 E-07
Total Lung Dose (Sv/Bq) 2.60 E-05
Case 1
1.16 E-07
2.12 E-06
8.54 E-06
4.52 E-06
2.66 E-07
1.56 E-05
Case 2
1.55 E-07
2.83 E-06
4.27 E-06
2.26 E-06
2.66 E-07
9.78 E-06
A-1
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Effective Dose (Sv/Bq) 4.47 E-05
3.43 E-05
2.85 E-05
IX ^Pu (slow rate of absorption). 1 urn AMAD. T^ = 24.065 years
(an alpha emitter)
Regional Lung Dose (Sv/Bq)
Lung Region Default
Bronchial, basal cells 8 .29 E-08
Bronchial, secretory cells 1.30 E-06
Bronchiolar 2.46 E-06
Alveolar-interstitial 5. 54 E-06
Lymph nodes 9.83 E-08
Total Lung Dose (Sv/Bq) 9.48 E-06
Effective Dose (Sv/Bq) 1.65 E-05
E. — Pu (slow rate of absorption). 5 um AMAD.
(an alpha emitter)
Regional Lung Dose (Sv/Bq)
Lung Region Default
Bronchial, basal cells 1.16 E-07
Bronchial, secretory cells 1.30 E-06
Bronchiolar 1.3 2 E-06
Alveolar-interstitial 2.76 E-06
Lymph nodes 5.85 E-08
Total Lung Dose (Sv/Bq) 5.56 E-06
Effective Dose (Sv/Bq) 9.26 E-06
F. — Sr (slow rate of absorption). 1 \im AMAD.
(a beta emitter)
Regional Lung Dose (Sv/Bq)
Lung Region Default
Bronchial, basal cells 1 .87 E-08
Bronchial, secretory cells 1.91 E-08
Bronchiolar 5. 18 E-08
Alveolar-interstitial 5. 47 E-08
Lymph nodes 3 . 24 E- 1 0
Case 1
1.49 E-07
2.34 E-06
2.22 E-06
1.66 E-06
9.83 E-08
6.47 E-06
1.35 E-05
Tr, = 24.065 vears
Case 1
2.09 E-07
2.34 E-06
1.19 E-06
8. 30 E-07
5.85 E-08
4.63 E-06
8.33 E-06
^,, = 29.12 vears
Case 1
3. 37 E-08
3. 44 E-08
4.66 E-08
1.64 E-08
3.24 E-10
Total Lung Dose (Sv/Bq) 1.45 E-07
Effective Dose (Sv/Bq) 1.49 E-07
1.31 E-07
1.36 E-07
Case 2
1.99 E-07
3.12 E-06
1.11 E-06
8.32 E-07
9.83 E-08
5.36 E-06
1.23 E-05
Case 2
2.78 E-07
3.12 E-06
5.96 E-07
4.15 E-07
5.85 E-08
4.47 E-06
8.17 E-06
Case 2
4.49 E-08
4.58 E-08
2.33 E-08
8.21 E-08
3.24 E-10
1.23 E-07
1.27 E-07
A-2
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G±mCs (fast rate of absorption). 0.1 urn AMAD. T12= 30.0 years
(a beta-gamma emitter)
Regional Lung Dose (Sv/Bq)
Lung Region Default Case 1 Case 2
Bronchial, basal cells 9.88E-11 1.77E-10 2.37 E-10
Bronchial, secretory cells 9.89E-11 1.78 E-10 2.37 E-10
Bronchiolar 1.98 E-10 1.78 E-10 8.90 E-ll
Alveolar-interstitial 1.96 E-10 5.88 E-ll 2.94 E-ll
Lymph nodes 5.87E-13 5.87E-13 5.87E-13
Total Lung Dose (Sv/Bq) 5.92 E-10 5.92 E-10 5.92 E-10
Effective Dose (Sv/Bq) 5.33 E-09 5.33 E-09 5.33 E-09
!L mCs (fast rate of absorption). 1 urn AMAD. T12= 30.0 years
(a beta-gamma emitter)
Regional Lung Dose (Sv/Bq)
Lung Region Default Case 1 Case 2
Bronchial, basal cells 8.59 E-ll 1.55 E-10 2.06 E-10
Bronchial, secretory cells 8.61 E-ll 1.55 E-10 2.07 E-10
Bronchiolar 1.71 E-10 1.54 E-10 7.68 E-ll
Alveolar-interstitial 1.70 E-10 5.11 E-l 1 2.56 E-ll
Lymphnodes 5.11E-13 5.11E-13 5.11E-13
Total Lung Dose (Sv/Bq) 5.13 E-10 5.15 E-10 5.16 E-10
Effective Dose (Sv/Bq) 4.72 E-09 4.72 E-09 4.72 E-09
L ml (fast rate of absorption). 1 urn AMAD. T1/2 = 8.04 days
(a beta-gamma emitter)
Regional Lung Dose (Sv/Bq)
Lung Region Default Case 1 Case 2
Bronchial, basal cells 1.77 E-12 3.20 E-12 4.26 E-12
Bronchial, secretory cells 1.99 E-12 3.58 E-12 4.78 E-12
Bronchiolar 2.46E-12 2.21 E-12 1.11 E-12
Alveolar-interstitial 2.04 E-12 6.14 E-13 3.07 E-13
Lymphnodes 5.83 E-15 5.83 E-15 5.83 E-15
Total Lung Dose (Sv/Bq) 8.27 E-12 9.61 E-12 1.05 E-ll
Effective Dose (Sv/Bq) 1.14 E-08 1.14 E-08 1.14 E-08
A-3
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«L mPo (moderate rate of absorption). 0.1 um AMAD. T^= 138.38 days
(an alpha emitter)
Regional Lung Dose (Sv/Bq)
Lung Region Default Case 1 Case 2
Bronchial, basal cells 4.27 E-08 7.68 E-08 1.02.E-07
Bronchial, secretory cells 8.36 E-07 1.50E-06 2.00 E-06
Bronchiolar 5.80 E-06 5.23 E-06 2.61 E-06
Alveolar-interstitial 1.04 E-06 3.12 E-07 1.56 E-07
Lymph nodes 3.60E-10 3.60E-10 3.60 E-10
Total Lung Dose (Sv/Bq) 7.72 E-06 7.12 E-06 4.87 E-06
Effective Dose (Sv/Bq) 7.86 E-06 7.26 E-06 5.02 E-06
K mPo (moderate rate of absorption). 1 urn AMAD. T1/2 = 138.38 days
(an alpha emitter)
Regional Lung Dose (Sv/Bq)
Lung Region Default Case 1 Case 2
Bronchial, basal cells 5.24 E-08 9.41 E-08 1.25 E-07
Bronchial, secretory cells 9.55 E-07 1.72 E-06 2.29 E-06
Bronchiolar 1.43 E-06 1.29 E-06 6.44 E-07
Alveolar-interstitial 3.83 E-07 1.15 E-07 5.75 E-08
Lymph nodes 1.37 E-10 1.37 E-10 1.37 E-10
Total Lung Dose (Sv/Bq) 2.82 E-06 3.21 E-06 3.11 E-06
Effective Dose (Sv/Bq) 2.90 E-06 3.29 E-06 3.20 E-06
Footnote to Table 1.
The doses are calculated for a standard worker: 31.3% of the time sitting and 68.76% doing light exercise.
The doses are per unit intake: Sv (Sieverts) per Bq (Becquerel). The software, LUDEP 1.1 (Personal
Computer Program for Calculating Internal doses Using the NEW ICRP Respiratory Tract Model)
(NRPB,1994), was used to calculate both committed weighted equivalent doses (abbreviated in the Table
as Regional Lung Dose and Total Lung Dose) and committed effective doses (abbreviated in the Table as
Effective Dose). Total Lung Doses are the sums of the committed weighted equivalent doses to all lung
regions given in the Table. The time of integration of the doses was 50 years after intake. The Effective
Doses given in the Table are the sums of the products of the committed tissue equivalent doses and the
appropriate tissue weighting factors for all tissues and organs in the body, including lungs, also integrated
over 50 years. This detail is not given in the Table.
The doses in the first column, Default, were calculated using the ICRP default values for apportioning the
lung weighting factor, 0.12. These are 16.67% to each the basal and secretory cells of the bronchial
epithelium, 33% to the bronchiolar epithelium and 33% to the alveolar-interstitial tissues. The doses in the
second column, Case 1, were calculated by apportioning the 0.12 weighting factor; 30% to each the basal
and secretory cells of the bronchial epithelium, 30% to the bronchiolar epithelium and 10% to the alveolar-
interstitial tissues. The doses in the third column, Case 2, were calculated by apportioning the 0.12 weight-
ing factor; 40% to each the basal and secretory cells of the bronchial epithelium, 15% to the bronchiolar
epithelium and 5% to the alveolar-interstitial tissues.
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APPENDIX B
GLOSSARY OF TERMS AND ACRONYMS AS USED IN THIS COMMENTARY
Absorption Transfer of inhaled material to body fluids such as circulating blood.
AMAD Activity Median Aerodynamic Diameter. Fifty percent of the activity
(aerodynamically classified) in the aerosol is associated with
particles of aerodynamic diameter greater than the AMAD. A log-
normal distribution of particle sizes is usually assumed.
Apportionment
Values Weighting factors assigned for the partition of tissue weighting
factor, 0.12, among regions of the lungs.
Alveolar-Interstitial
Region Consists of the respiratory bronchioles, alveolar ducts and sacs with
their alveoli, and the interstitial connective tissues; airway
generations 16 and beyond.
Basal Cells Cuboidal epithelial cells attached to the basement membrane of
extrathoracic and bronchial epithelium and not extending to the
surface.
Bronchial Region Consists of the trachea and bronchi; airway generations 1 through
8.
Bronchiolar Region Consists of the bronchioles and terminal bronchioles; airway
generations 9 through 15.
Bq Becquerel: the special name for the SI (International System of
units) unit of radioactivity;
1 Bq = 1 disintegration per second.
Cs Cesium and its radioactive isotope, 137Cs, a beta-gamma emitter.
Deposition Refers to the initial processes determining how much of the material
in the inspired air remains behind in the respiratory tract after
exhalation.
Default Values Numerical values taken when specific information is deficient.
E Exponent, expressed here in powers of ten.
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Effective Dose
Committed
Effective Dose
EPA
Exposure
Extrathoracic
Gy
Equivalent Dose
Committed
Equivalent Dose
Intake
ICRP
E The sum of the weighted equivalent doses in all tissues of the
body.
E(r) The sum of the products of the committed tissue equivalent
doses and the appropriate tissue weighting factors (WT) for all
tissues and organs of the body, where r is the integration time in
years following intake of radioactive material into the body, 50 years
for adults and from intake to age 70 years for children.
The United States Environmental Protection Agency
Refers to the potential for receiving a radiation dose by being in the
presence of airborne radionuclides or near a beam of neutrons, x-or
gamma-rays.
Refers to regions of the respiratory tract that are outside of the
thorax: anterior nose, posterior nasal passages, mouth, pharynx
and larynx.
Gray: the special name for the SI (International System of units)
unit of absorbed dose:
1 Gy = 1 joule per kilogram..
HT The product of the averaged absorbed dose in a tissue or organ
T and the radiation weighting factor (WR ) for the radiation type.
/-/T(r) The time integral of the equivalent dose rate in a particular
tissue or organ that will be received by an individual following intake
of radioactive material into the body where r is the integration time
in years following intake, 50 years for adults and from intake to age
70 years for children.
Activity that enters the respiratory tract or gastrointestinal tract from
the environment.
Iodine and its radioactive isotope, 131I, a beta-gamma emitter.
International Commission on Radiological Protection. The ICRP was
established in 1928 by the Second International Congress of
Radiology to provide general guidance and recommendations on the safe
use of radiation and radioactive materials in medicine, education, research
and industry. It works closely with its sister organization, the International
Commission on Radiation Units and Measurements, and has official
B-2
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relationships with the World Health Organization and the International
Atomic Energy Agency. It also interacts with numerous other international
organizations on matters of radiation protection.
LUDEP Personal computer program for calculating internal doses using the new
ICRP biokinetic respiratory tract model (Version 1.0, 1.1, 2.0, etc.)
Lymph Nodes Accumulations of lymphatic tissue about 1 to 25 mm in diameter,
located along lymphatic vessels between tissues and organs, that
filter bacteria and foreign materials from the lymph, a transparent
fluid that is drained from tissues and returned to the blood.
mm millimeter (one thousandth of a meter)
NCRP National Council on Radiation Protection and Measurements The NCRP
was originally established in 1929 as the Advisory Committee on X-ray and
Radium Protection to the National Bureau of Standards, at the
recommendation of the ICRP, and renamed the National Committee on
Radiation Protection in 1946 with the addition of several parent
organizations including the armed forces, professional medical societies
and the National Electrical Manufacturers Association. In 1964 the NCRP
was chartered by Congress as a non-profit organization to collect, analyze,
develop and disseminate in the public interest information and
recommendations about radiation protection; provide means for
cooperation of organizations interested in radiation matters; develop basic
concepts about radiation topics and their application; and to cooperate
with the ICRP and other international organizations concerned with
radiation protection.
NRPB National Radiological Protection Board of England
ORIA Office of Radiation and Indoor Air (U.S. EPA)
ORP Office of Radiation Programs (U.S. EPA) (Forerunner of ORIA)
Pu Plutonium and its radioactive isotopes, 238Pu and 239Pu, both alpha
emitters.
Po Polonium and its radioactive isotope, 210Po, an alpha emitter.
RAC Radiation Advisory Committee (U.S. EPA/SAB/RAC)
rem roentgen equivalent man: the unit of dose equivalent)
B-3
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SAB Science Advisory Board (U.S. EPA)
Secretory Cells Nonciliated epithelial cells that have mucous or serous secretions.
Sr
Sv
1 1/2
TGLD
Thoracic
urn
Strontium and its radioactive isotope, Sr, a beta emitter.
Sievert: the special name for the S.I. (International System of units)
unit of equivalent dose (HT) and effective dose (E): 1 Sv = 1 joule per
kilogram), equal to 100 rem.
Radioactive Half-life: The time taken for the activity of a radioactive
material to lose half its value by decay, generally with the emission of
alpha, beta, gamma or neutron radiations.
lask Group on Lung Dynamics (1966 task group of ICRP)
Refers to the regions of the respiratory tract that are contained within the
thorax: bronchial, bronchiolar and alveolar-interstitial regions.
Micrometer: 10"4 mm.
Radiation Weighting
Factor WR A dimensionless factor to derive the equivalent dose from the
absorbed dose averaged over a tissue or organ and is based on the
quality of radiation.
Tissue Weighting
Factor WT The factor by which the equivalent dose in a tissue or organ is
weighted to represent the relative contribution of that tissue or organ to the
total detriment resulting from uniform irradiation of the body.
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REFERENCES
EPA . 1994. Estimating Radiogenic Cancer Risks. EPA 402-R-93-076, June 1994.
ICRP. 1960. Recommendations of the International Commission on Radiological Protection.
Report of Committee II on Permissible Dose for Internal Radiation (1959), ICRP
Publication 2.
ICRP. 1979. Limits for Intakes of Radionuclides by Workers: Part 1. ICRP Publication 30.
ICRP. 1981. Limits for Inhalation of Radon Daughters by Workers. ICRP Publication 32.
ICRP. 1989. Age-dependent Doses to Members of the Public from Intake of Radionuclides: Part
1. ICRP Publication 56.
ICRP. 1991. 7990 Recommendations of the International Commission on Radiological Protection.
ICRP Publication 60.
ICRP. 1993. Protection Against Radon-222 at Home and at Work. ICRP Publication 65.
ICRP. 1993a. Age-dependent Doses to Members of the Public from Intake of Radionuclides: Part
2, Ingestion Coefficients. ICRP Publication 67.
ICRP. 1994. Human Respiratory Tract Model for Radiological Protection. ICRP Publication 66.
ICRP. 1994a. Dose Coefficients for Intakes of Radionuclides by Workers. ICRP Publication 68.
ICRP. 1995. Age-dependent Doses to Members of the Public from Intake of Radionuclides: Part
3, Ingestion Dose Coefficients. ICRP Publication 69.
ICRP. 1995a. Age-dependent Doses to Members of the Public from Intake of Radionuclides: Part
4, Inhalation Dose Coefficients. ICRP Publication 71.
NCRP. 1987. Exposure of the Population of the United States and Canada from Natural Back-
ground Radiation. NCRP Report 94.
NRPB. 1994. LUDEP 1.0, Personal Computer Program for Calculating Internal Doses Using the
New ICRP Respiratory Tract Model. National Radiological Protection Board, NRPB-SR264
Taylor, L. S. . 1984. The Tri-Partite Conferences on Radiation Protection, Canada, United States
(1949-1953). U.S. DOE Report HVO-270 (DE 84016028), U.S. Department of Energy,
Office of scientific and Technical Information, Washington, D.C.
TGLD . 1966. Deposition and retention models for internal dosimetry of the human respiratory
tract. Health Phys. Task Group on Lung Dynamics (TGLD), 12, 173-207.
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U.S. ENVIRONMENTAL PROTECTION AGENCY
SCIENCE ADVISORY BOARD
RADIATION ADVISORY COMMITTEE
Chair
Dr. James E. Watson, Jr., Professor, Department of Environmental Sciences and
Engineering, University of North Carolina at Chapel Hill, NC
Members and Consultants
Dr. William J. Bair, (Retired) Former Manager, Life Sciences Center, Battelle Pacific
Northwest Laboratory, Richland, WA
Dr. Stephen L. Brown, Director, R2C2 (Risks of Radiation and Chemical Compounds),
Oakland, CA
Dr. June Fabryka-Martin, Staff Scientist, Chemical Science and Technology Division, Los
Alamos National laboratory, Los Alamos, NM
Dr. Ricardo Gonzalez, Associate Professor, Department of Radiological Sciences,
University of Puerto Rico School of Medicine, San Juan, PR
Dr. David G. Hoel, Chairman and Professor, Department of Biometry and Epidemiology,
Medical University of South Carolina, Charleston, SC
Dr. F. Owen Hoffman, President, SENES Oak Ridge, Inc., Center for Risk Analysis, Oak
Ridge, TN
Dr. Janet Johnson, Senior Radiation Scientist, Sheperd Miller, Inc., Fort Collins, CO
Dr. Bernd Kahn, Professor, School of Nuclear Engineering and Health Physics, and
Director, Environmental Resources Center, Georgia Institute of Technology, Atlanta, GA
Dr. Ellen Mangione, M.D., M.P.H., Director, Disease Control and Environmental
Epidemiology Division, Colorado Department of Health, Denver, CO
Dr. Paul J. Merges, Chief, Bureau of Pesticides & Radiation, Division of Solid &
Hazardous Materials, New York State Department of Environmental Conservation, Albany,
NY
Science Advisory Board Staff
Dr. K. Jack Kooyoomjian, Designated Federal Official, U.S. EPA, Science Advisory Board
(1400), 401 M Street, S.W., Washington, DC 20460
Ms. Diana L. Pozun, Staff Secretary, U.S. EPA, Science Advisory Board (1400), 401 M
Street, S.W., Washington, DC 20460
Dr. Donald G. Barnes, Staff Director, Science Advisory Board
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NOTICE
This commentary has been written as part of the activities of the Science Advisory
Board, a public advisory group providing extramural scientific information and advice to the
Administrator and other officials of the Environmental Protection Agency. The Board is
structured to provide a balanced, expert assessment of scientific matters related to
problems facing the Agency. This commentary has not been reviewed for approval by the
Agency and, hence, the contents of this commentary do not necessarily represent the
views and policies of the Environmental Protection Agency, nor of other agencies in the
Executive Branch of the Federal Government, nor does mention of trade names or
commercial products constitute endorsement or recommendation for use.
The Radiation Advisory Committee (RAC) wishes to acknowledge with grateful
appreciation that the bulk of this commentary was prepared by Dr. William J Bair, a
member of the RAC.
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ABSTRACT
The Radiation Advisory Committee (RAC) of the Science Advisory Board (SAB)
prepared this commentary on the scientific basis for apportioning risk among the
International Commission on Radiation Protection (ICRP) Publication 66 regions of the
respiratory tract in response to concerns raised by the Office of Radiation and Indoor Air
(ORIA) within the Office of Air and Radiation (OAR). In this commentary it is concluded
that the current use of the default values recommended by the ICRP would not have a
major impact on radiation protection. Nevertheless, the EPA is encouraged to undertake
an effort to provide a more scientifically acceptable basis for apportioning the tissue
weighting factor for the lungs. This could involve reexamining the literature for data on the
relative radiation sensitivity of the several regions of the lungs, including more recent
results from epidemiology studies and animal experiments as well as studies that might
identify the frequency distribution of radiation sensitive cells in the various tissues in the
lungs.
The RAC noted that an EPA Effort that resulted in a scheme for apportioning the
lung tissue risk weighting factor that was acceptable to the ICRP and the NCRP (National
Council on Radiation Protection and Measurements) would be welcomed by the radiation
protection community. The Committee also noted that the adoption of values by the EPA
independent of the ICRP and the NCRP would cause unneeded confusion in the
calculation of effective doses in the United States.
Key Words: Lung model, ICRP Human Respiratory Tract Model for Radiological
Protection, Committed Effective Dose, Committed Equivalent Lung Dose, Dose
Calculations, Tissue Weighting Factor.
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