Nondetectable Workshop

Historic Overview of Internal
Monitoring Methods: Bill Moss

Mr. Moss presented information on the
methods used to determine internal doses
from plutonium exposures. The evolution
of plutonium radiochemistry procedures,
LODs, and potential problems in the
dosimetry records were summarized. Due
to time constraints and the nature of the
material presented, it was decided that a
detailed discussion on internal radiation
doses and their applicability to
epidemiology should be tabled for a future
workshop. However, several problems
with the dosimetry data were mentioned in
his presentation which could have an effect
in a risk assessment. Specific limitations
mentioned include: residual material
contaminating laboratory equipment
causing a false-positive, difficulties in
obtaining 24 hour fecal and/or urine
samples, computer modelling limitations,
biokinetic variations, lag time in analyses,
chronic vs. acute intake determinations,
and parent to decay product relationships
within the body and determining organ
doses.

Detection Limit Quandary and
Missed Dose Concepts: Allen Brodsky

Dr. Brodsky presented data and
information related to the problem of
estimating radiation doses of populations
under study for radiation risk assessment.
Particular emphasis was placed on that
portion of the population whose radiation
doses were below the limit of detection or

were biased in some other manner. Topics
in his presentation included:

© Resources useful in defining LODs
@® Sources and magnitudes of errors in
dosimetry.

A brief summary of his presentation
follows, additional information is available
in the references.

Resources useful in defining limits of
detection:

Historical definitions for detection
capability varied considerably from site to
site. For example, various formulas used
were two times background or two or three
times the standard deviation of the blank.
The Health Physics Society (HPS)
organized a working group to review the
literature on the statistical basis of
detection limits. Their recommendations
were based mainly on Currie's work.”
NUREG-1156 describes how the concepts
of LOD can be applied to measurements
other than the counting process and
discusses the concepts of bias and
precision.”

Sources and magnitudes of errors in
dosimetry:

A personnel dosimeter yields a point
estimate of exposure at the position of the
dosimeter on the worker, not a whole body
exposure. If a dosimeter result was below
a "subjective impression of a detectable
amount” (or a minimum detectable dose), a
zero dose would be recorded.
Alternatively, a more conservative
approach is to assign a dose equal to the
LOD to ensure that the worker's



Nondetectable Workshop

Figure 1
Pocket lon Chamber

A. Low Atomic Number Wall E;. Polyethylene Insulating Washer

B. Graphite-Coated Paper Shell E,. Polystyrene Fixed Bushing

C. Aluminum Terminal Head E;. Electrode Contact

D. Aluminum Terminal Sleeve F. Retaining Ring

E,. Polystyrene Support Bushing G,. Aluminum Base Cap

E,. Central Electrode, Graphite Coated G,. Polyethylene Friction Bushing

Limitations: e@ PICs can only measure gamma and
"hard" betas, (specificity).

Use of PIC data in epidemiology must be @ Physical sensitivity; and

carefully evaluated because of the @ Frequent false-positive readings.

following limitations:

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Nondetectable Workshop

procedure. If this
documentation is not
available, then the
adjusted dose should
represent the sum of the
PIC results. Case (2)

Matrix for Supplementing Film Badge with PIC readings

CLOSED WINDOW film result

0 >0

was adopted to be OPEN
consistent with case (1) WINDOW

true zero invalid film or true zero

such that the PIC results fj} film
could be incorporated to J result
confirmed positive
weekly results.

The matrix also
indicates that any film
dosimeter result having
an open window dose
equal to zero but showing a positive closed
window result is highly suspicious since
the open window portion of the film would
have to show at least the same exposure as
the closed window portion of the film.
This feature would be applicable to all
facilities using the film dosimeter since all
designs included the open/closed windows
to differentiate beta and low energy x-ray
exposure from high energy photons.
Therefore, site specific data should be
obtained on the dosimetry program to
support the retrospective interpretation of
the films.

A recommendation to combine populations
across the DOE complex was considered
premature because each site has unique
dosimetry problems that have to be
resolved before the data could be
considered comparable. It was agreed that
the ultimate goal should be to quantify

see equation below Use Film Result

Case (1)

ADJUSTED DOSE = (PICs) +Open Window
2

exposures on a site-by-site basis. Where
appropriate, the data could then be
combined for working populations across
the sites rather than start with a qualitative
approach.

An alternative recommendation was made
that exposures across the DOE facilities
could be compared if site-specific, annual
mean doses were determined. Since
epidemiologic studies often divide exposed
workers into groups based upon dose
(exposure), it may be possible to compare
worker cohort groups. It was concluded
that individual doses were desirable
whenever possible since the mean is not an
adequate descriptor of exposure variation.
Therefore, the uncertainty in the dose
estimates should be determined since the
objective of the epidemiologic study is to
determine the risk per unit of dose. The
workshop members agreed, in principle,
that exposure assessments would have to
be conducted on a site by site basis. This
would allow individual problems at each
site (especially those related to internal

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Nondetectable Workshop

TABLE 1°
Tha Dept of Boerey earns Cones ies TN

varied over time from site to site due to
several factors:

Administrative practices.

Security measures (classified
materials).
© Record keeping practices.

Measurement technology limitations.

Regulatory compliance requirements.

© Lack of overall direction or
standardization for such a program.

These factors resulted in dosimetry data
which, as recorded, are biased in some
manner. At some facilities many workers’
dosimeters were read weekly, and during
some periods, film dosimeter results less
than the minimum detectable level were set
to zero. In other instances, a reading at or

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Nondetectable Workshop

cumulative dose would not exceed the
regulatory limits. This was illustrated
earlier in "Dose Below the Limit of
Detection.” However, even these practices
changed over time and from site to site.

Dr. Brodsky also described relevant
sources of uncertainty in both the
measurement and in the conversion of the
measurement result to dose. Estimating
the uncertainty associated with missed
doses or the bias in dose estimates requires
knowledge of errors, error distributions,
and the statistical characteristics of the
underlying exposure distributions. In
addition, he described the energy response
characteristics of film dosimeters and some
of the improvements in densitometry
during the 1960s. Density calibration
curves for different types of film and -
dosimeters were also described including
the variance observed in intercomparison
measurements. The influence of
temperature and relative humidity on the
cumulative quarterly dose assigned to film
dosimeters that were exchanged at different
frequencies does not limit the precision of
the weekly films, except for high
temperature/high humidity conditions
under which many films were lost.'°

In summary, Dr. Brodsky showed that
many populations have lognormal exposure
distributions repeatedly, year after year.
The average exposures, or population
exposures, of low-dose portions of
monitored populations can often be
assessed assuming that the shape of the
exposure distribution is lognormal below
an annual dose of 10 mSv (1 rem). A
cumulative plot of the exposure data can
usually be fitted by a straight line in the
region from 1 to 10 mSv (0.1 to 1.0 rem),

which can then be extrapolated to lower
exposure regions for assessing the average
doses. This analysis can be applied to
portions of the population or to the total
population for doses below about 1 mSv
(0.1 rem). *

External Exposures at ORNL and
Their implications for Epidemiology:
Steve Wing :

Dr. Wing recommended evaluating the
distribution of doses recorded over time
and expressed the critical need to have
accurate radiation exposure data on
individuals to properly assess radiation-
mortality associations. He discussed
changes in recorded doses and in radiation
monitoring programs at Oak Ridge
National Laboratory. Numerous changes
in monitoring programs occurred between
1943 and 1984, including the types of
dosimeters used, the frequency of reading
dosimeters, methods of calculating doses,
and practices of recording doses.
Temporal patterns of doses in the lower
range of the distribution suggest changes in
policies and practices for recording doses.
These changes could influence dose values
used in epidemiological studies. Reliable
and accurate exposure measurements are
especially important in studies of low level
exposures due to small differences in
outcomes between exposure groups.
Changes in recorded doses due to
monitoring and recording practices
emphasize the need for comparable
epidemiological studies of radiation
mortality associations in other
populations.”

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Strom DJ. Estimating Individual and Collective Doses to Groups With ‘Less than Detectable’
Doses: A Method for Use in Epidemiologic Studies. Health Phys. 51(4):437-445, 1986.

Strom DJ. LONGNORML. (Earlier version: LPROBIT). Oak Ridge, TN: Radiation
Shielding Information Center Code No. PSR-370; RSIC Newsletter 325:5, December, 1991.

Taylor NA. Estimation of dose received when dosemeter results are recorded below a
threshold level. J. Radiol Prot.11(3): 191-198, 1991.

Troyer GL, Jones RA, Jensen L. The Utility of Reporting Negative Counting Values.
Radioactivity and Radiochemistry 2(2):48-56, 1991.

Waite DA. Interpretation of Environmental Radioactivity Measurements. In: CRC Handbook
of Environmental Radiation, AW Klement, Ed. Boca Raton: Chemical Rubber Company,
1982.

Waters MA, Selvin S, Rappaport SM. A Measure of Goodness-of-Fit for the Lognormal
Model Applied to Occupational Exposures. ‘Amer. Ind. Hyg. Assoc. J. 52(1):493-502, 1991.

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Nondetectable Workshop

approach used by ORISE, but has the
advantage of addressing problems in both
bias and uncertainty (precision) rather than
bias alone.

Workshop Discussion: Use of PIC
Data in Epidemiology

After their presentation, a workshop
discussion attempted to resolve the
question pertaining to use of the PIC as a
supplement to the film dosimeter result.
The approach that was described focused
on the Oak Ridge National Lab cohort
between the time periods where PICs and
film badges were worn side by side.
Records for the daily PIC results were
compared with weekly results for the film
dosimeter. One option for using PIC data
is when a zero dose (or notional dose)
recorded for the weekly film result is
reported. Film results could be replaced
by summing the daily results obtained from
the PIC. However, this task required
extensive data entry and increased cost to
improve the ORNL data.

An alternative recommendation was made
to evaluate the open and closed window
results from the film badge to confirm that
the dose was truly a zero. A recorded non-
penetrating or shallow dose based on the
response of the open window component of
the film dosimeter can be an additional
important source of information to
ascertain the significance of deep dose non-
detectable results. An open window dose
has no absorbers, allowing all radiation to
expose the film. Therefore, the open
window portion of the film would always
have a positive reading if any exposure
occurred. A truly zero dose occurs when

the open window dose on a film badge is
Tread as zero exposure.

Recommendations were made for using
daily PIC data to supplement weekly film
badge results if the closed window dose
(deep dose) estimates have been recorded
as zero. This method is similar to that
proposed for use at the Oak Ridge National
Lab to alleviate data censoring.

The combination of PIC data and film
results could be used if historical data
censoring was found to be a problem.

A matrix was developed during the
workshop discussion session, which
describes the logic for using PIC data in an
exposure assessment. This matrix was
suggested as a method to validate the true
zero doses recorded from the film
dosimeters by interpreting the open
window and closed window results. The
sum of daily PIC results to supplement the
weekly film dosimeter result whenever:

© The film dosimeter open window dose
was greater than zero (suggesting some
low energy exposure) but the
penetrating dose was recorded as zero.
or
®@ To validate positive film dosimeter
results using PIC data.

Case (1) was adopted in recognition of the
sensitivity of the open window portion of
the film dosimeter in detecting both beta
particles and low energy photons. Since it
is not known when such exposures were
received, a conservative approach is taken
to report the result from the adjusted dose
equation as the true dose that will be used
in the epidemiologic analysis. This
requires documentation on the calibration

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Nondetectable Workshop

risk factors because the cumulative
exposure estimates are underestimated.
Knowledge about frequency change out is
important for a proper exposure
assessment.

Another limitation of the earlier film
badges is the sensitivity to photon energies
below 100 keV. Facilities that processed
radionuclides that decayed with photon
energies below 100 keV are likely to have
higher than true exposure results.
Knowledge about dosimetry algorithms
used at that time could determine if the
over response was accounted for in the
record.

Reporting units of the film badge doses
changed over time. The original unit of
measure was the roentgen, an exposure
unit not a dose unit. The dose unit was the
rep, roentgen equivalent physical which,
for most photon energies, was equal to the
roentgen. Later, the rep became the rem,
roentgen equivalent man. Historical
dosimetry data reported in different units
must be converted to a common unit prior
to the epidemiologic analysis. This
limitation is of particular importance,
especially in estimating a dose due to
neutron exposures, in which the conversion
from roentgen to rem is not equivocal.

Neutron dosimetry introduces other
limitations because different procedures are
used to determine a person's dose. An
intense effort is required by a trained
technician to count microscopic tracks
created by a re-coiled proton particle in the
film. Depending on the initial neutron
energy, some tracks are easier to identify
than others. Limitations associated with
neutron dosimetry include: labor intensive

work, the need for highly trained
technicians, and fading of up to 30% of the
original reading may occur during storage.
Most of these limitations can be taken into
account today by advanced computer
software packages and programs.

Workshop Discussion: External
Dosimetry Issues

Additional contributions were provided by
Dan Strom, Jack Fix, Hap West, and Bill
Tankersley based upon their experience
and research dealing with PICs and film
dosimeters. The main focus of their
discussion was directed at developing
recommendations for evaluating external
dosimetry data recorded as zero, censored,
missing, or shown with a notation such as
<LOD. Dan Strom provided a list of
papers and reports that specifically address
the issues covered in this workshop
(Appendix A). Bill Tankersley presented
material on an approach for supplementing
missing or censored film dosimeter data
with measurements from PICs.”

Biases:

Several sources of bias were identified as a
result of this discussion, such as
assignment of zero dose whenever Tesults
were missing or unusual. Other practices
were less extreme, such as interpolating
lost results or assignment of the dose from
aco-worker when an individual's results
were lost or questionable. Average doses
for a department or plant have also been
assigned to workers in an attempt to
replace lost or missing measurements. A
more complete discussion on the generai
issue of uncertainty in individual dose
estimates in epidemiologic studies of

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Nondetectable Workshop

Alternative Methods for Handling
Missed Dose, and Censored and
Notional Data:

If the number of missed dose estimates and
left-censored results is minimal, or if
notional dose estimates are not desirable,
other methods can be used to replace such
data in epidemiologic analyses. One
method would be to reconstruct exposure
estimates from area air monitoring or
direct radiation measurement data. This
approach has several limitations which
must be recognized and evaluated to
determine its feasibility. Also, all
associated assumptions and supporting
information should be documented. For
example, the purpose and scope of area
monitoring must be determined and
evaluated with regard to its intended use.
The historical purposes for area sampling,
e.g., compliance, hazard evaluation,
control technology assessment, or safety
alarm limits, inherently limits its utility to
derive exposure estimates for
epidemiology. Sampling duration,
sensitivity, specificity, and purpose for
sampling are all parameters for
consideration. For example, short-term
grab samples with a relatively high
detection limit used to identify emission
points in a process area may not be suitable
for use in this regard. However using a
measure of central tendency for integrated
continuous area monitoring over several
years with documentation on location of
workers and time spent in the area may be
very useable. This approach requires
considerable expert judgement and
documentation of the rationale.

Use of area monitoring data is most likely
adaptable for assigning exposure estimates

to individuals or homogeneous groupings
via a Job Exposure Matrix (JEM), defined
below. Such assignment of exposure
estimates requires identification of
workplaces, work departments, and job
titles over the history of the site. This task
may be done in a unified way, with
creation of a detailed multi-dimensional
matrix incorporating information on
standardized job titles, departmental
assignments, building locations, process
changes, work practices, and periods of
work through time. Groupings of
homogeneous exposure by job tasks, job
titles, departments, or building location can
be based on all available information,
technical judgement, or statistical modeling
of available exposure monitoring data.

The dimensions of the matrix depend on
the number of variables and the amount of
information available in each variable.

Workshop Discussion: Epidemiologic
Uses of Non-detectable Values; JEM

The discussion session following Dr.
Ruttenber's presentation focused on
alternatives to notional doses.
Considerable time was spent discussing the
best way to use the actual recorded
personal doses and area monitoring data in
a manner that would not bias the
epidemiologic outcomes, while taking into
account the limitations of the historical
data. The usefulness of developing a JEM
dominated the session.

A JEM provides radiation exposure
estimates for a group of workers based
upon a common exposure experience.”
Specific information on job titles, building
or department codes and/or process tasks
are examples of a common experience

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24. Brodsky A. "Statistical Methods of Data Analysis,” in Handbook of Radiation
Measurement and Protection, Section A. Vol. II: Mathematical and Biological
Information, CRC Press, Boca Raton, FL, 1982.

25. Wing S, et al. "Recording of External Radiation Exposures at Oak Ridge National
Laboratory: Implications for Epidemiological Studies," Exp. Analy. and Environ. Epi. J.,
4, (1), 1994.

26. Watkins JP, et al. Data Collection, Validation, and Description for Oak Ridge Nuclear
Facilities Mortality Study. ORISE Technical Report #9315-42.

27. Mitchell TM, et al. "A Method for Estimating Occupational Radiation Dose to
Individuals, Using Weekly Dosimetry Data." ORNL Report # 7668, December 1993.



Nondetectable Workshop

@ Historic uses of non-detectable data in
epidemiology.

® Historic overviews of both internal and
external monitoring methods.

® Detection limit quandary and missed
dose concepts.

@ One solution/approach used on an Oak
Ridge cohort.

Prior to the workshop, several technical
issues related to the assessment of
occupational radiation exposures were
identified. Listed below are specific
concerns on external and internal exposure
data affecting exposure assessment
strategies used for epidemiologic purposes.

External Exposure Data

© Changes in dosimeters and detection
limits over time.

@ Identification/separation of true zero
dose results from true positive results.

© Impact of dosimeter exchange
frequency upon measurement
sensitivity.

© Imputation strategies (e.g., simple one
value, multifactor, or stochastic
approach).

© Site-specific practices (detection levels,
energy response).

Internal Exposure Data (urinalysis and in
vivo measurements)

© Methods for analyzing different
radionuclides.

© Identification of true zero results from
censored results.

© Change in sensitivity of method over
time.

@ Changes in sampling methods over
time.

© Quantitative vs. qualitative methods.

e Effects of sampling frequency.

NIOSH is attempting to establish methods
and procedures to be used in interpreting
historical occupational exposure data that
may have been censored or recorded as
zero for use in epidemiologic analyses.
The workshop was arranged in a manner to
review each of the main areas listed in the
objective and to address these technical
issues. This served three purposes. First,
it provided the workshop participants with
a baseline for interpreting past dosimetry
results from these facilities. Second, it
served as a foundation for discussing how
these results should be addressed in
epidemiologic studies. And finally, it
allowed NIOSH researchers to become
familiar with the radiation monitoring and
record keeping practices and procedures
used at different times and at different
facilities throughout the DOE complex.

The term Limit of Detection (LOD) as
used in this document is defined as the
smallest reading which can be
distinguished from a background reading
based on stated statistical assumptions.
LOD may then be equated with detection
level, minimum detectable activity, or
minimum detectable dose. The term LOD
is used throughout this document for
consistency and the phrases "use of non-
detected values” or "less than the LOD" or

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below this subjective detection limit was
recorded as an exposure or a dose at that
limit to ensure that cumulative exposures
or doses were not underestimated.’ A third
way of recording non-detectable results
was to assign some other "administrative"
value such as half the minimal detectable
level or a value selected by an established
procedure.‘ All of the above factors affect
the quality and content of historical
exposure data. The influence this type of
data has on bias and misclassification, and
recommended methods for treatment and
use of these data in epidemiologic analysis
has been the subject of discussion by
several authors.?*“**"*" Knowledge about
these factors, ways to record dose results,
and the methods to treat and use these data
are required to accurately assess doses used
for risk estimation in epidemiologic
studies. All of this information served as
the center of discussion for this workshop.

The Department of Health and Human
Services (DHHS) is responsible for
managing and conducting both community
and occupational epidemiologic studies at
Department of Energy facilities. This
responsibility was transferred to DHHS
through a Memorandum of Understanding
between the two agencies in late 1990.
The National Institute for Occupational
Safety and Health (NIOSH) is the agency
within DHHS that is responsible for
studying the relationships between health
outcomes and occupational exposures to
radiation, chemicals, and other hazards at
these facilities.

Historical records and accurate exposure
assessments of various hazards play a vital
role in these studies. Changes in
measurement technology, administrative
practices, regulatory requirements,
protection philosophy, and security
measures have occurred throughout a fifty-
year time period. Every one of these
aspects may influence the accuracy and
reliability of exposure estimates used in
current and future epidemiologic studies.

NIOSH has initiated a project called
"Research Issues Workshop” to address
these changes specifically and to determine
how they might affect exposure estimates
used in epidemiology. This project is
conducted through a series of workshops
which bring together recognized experts in
dosimetry, epidemiology, biostatistics, and
exposure assessment. A workshop setting
was chosen because of its inherent
flexibility and ability to involve more
scientists in creative problem-solving
discussions. This paper serves as a
summary of the proceedings from the first
workshop sponsored by NIOSH in
September 1993.

The objective of the first workshop was to
determine the optimal use of “censored” or
“non-detectable" radiation monitoring data
in future epidemiologic studies of radiation
exposed workers. Several speakers from
various disciplines presented talks which
served as a basis for discussion on this
topic. The presentations covered four
main areas:

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Nondetectable Workshop

nuclear workers is presented in several
references.*"*""

Missed Dose Concept:

The missed dose concept was introduced as
another source of bias. The degree to
which the limited sensitivity of a dosimeter
can increase the dose missed depends on
the frequency with which it was
exchanged. To illustrate this trait, assume
that the sensitivity (LOD) of each
dosimeter worn by a worker was 0,2 mSv
(20 mrem) and that this was the worker's
average dose during the monitoring period.
If that dose was reported as being below
the LOD, then a monthly badge exchange
would introduce an effective detection
threshold of 2.4 mSv/yr (240 mrem/yr).
This assumes that the dosimeter reading is
recorded as zero or <0.2 mSv every
month. If it was recorded as <0.2 mSv
fifty percent of the time and 0.2 mSv the
remaining fifty percent, then the resulting
effective detection threshold would be

1.2 mSv/yr (120 mrem/yr). Similarly, the
impact of a missed dose could be greater
for a weekly exchange period, a common
practice throughout the DOE complex
during the 1940s and early 1950s, resulting
in a potential missed dose equal to 10
mSv/yr (0.2 mSv per week x 50 working
weeks per year) or 5 mSv/yr assuming fifty
percent probability.

Another factor making the missed dose
concept a significant problem is the lack of
quantitative information on the precision
and accuracy of routine calibrations.
Detection limits are often quoted between
0.2 to 0.4 mSv (20 - 40 mrem) but may
not reflect the actual performance of the
detector corrected for background.

Jack Fix noted in a post-workshop letter
that:

"An important re-occurring concept of the
workshop discussion is the significance of
the LOD, of about 0.3 mSv, for the
individual film results. For example, there
is discussion of the potential annual missed
dose if film dosimeters are exchanged
weekly. However, I believe this topic is
much more complicated. Personnel dose is
typically calculated from the difference
between the response of personnel film and
the response of the background film. There
is variability in both of these quantities,
likely about 0.1 mSv. As such, the true
question is the significance of the
differences between personnel and
background film, each with a detection
level of about 0.3 mSv and a variability of
about 0.1 mSv. For truly background
data, the case can be made that too much
dose will be recorded. Another perspective
is the true detection level for cases where
all reported values are zero for the same
individual in the same work environment.
The actual non-truncated values can be
represented by a distribution of values.
Assuming the detection level is 0.3 mSv
and there are 50 independent observations,
then a maximum of 1% of the. area of the
distribution would lie above 0.3 mSv for a
normal distribution. In fact, the area will
be less than 1% if the skewness of the
distribution for low dose results is
considered. This entire area involves
several complex issues. Likely only actual
near-zero laboratory data can resolve these
issues with confidence.”

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Nondetectable Workshop

The following sections represent highlights
of each of the speakers’ presentations and
summary remarks from the other workshop
attendants.

Historic Uses of Non-Detectable
Data in Epidemiology: . Jim Ruttenber

Dr. Ruttenber opened the workshop with a
review of how non-detectable values have
been used in past epidemiologic studies.
Four areas were covered :

© Classifications of Missing Dose Data in
Epidemiology.

® Ways to Record Doses Below LOD.

® Notional Dose Estimates Based on
LOD.

® Alternatives to Notional Doses.

Each topic is summarized in the following
paragraphs.

Missing Dose Data:

Missing dose, censored, or non-detectable
data have been encountered in past
epidemiologic studies as a result of the
following situations:

Lost data.

Strict monitoring criteria.
Inadequate monitoring.

Errors in monitoring.

Exposure values recorded below the
limit of detection.

Notional dose estimates are commonly
used as surrogate exposure estimates when
an abnormal event occurs such as an

invalid result, a lost dosimeter, or a
worker's dosimeter cannot be processed.
Notional doses are entries recorded in the
exposure files as a quantity related to an
administrative limit or minimum detectable
reading (e.g., <LOD). This would tend
to "left-censor” the dose distribution.

Doses Below the Limit of Detection:

Handling data which fall below the LOD is
problematic and can lead to bias in the
epidemiologic analysis. For example, if
the portion of exposure data representing
zeros is adjusted by setting the exposure
equal to the LOD, then the cumulative
dosé would likely be overestimated, thus
affecting the risk estimates calculated in the
analysis. In addition to this method, other
ways to utilize data below the LOD
include: assigning some fixed number that
falls between zero and the LOD, LOD/V2,
assigning zero, using a notional estimate
based on area monitoring data, or applying
some alternative method based on the LOD
as described below.

Notional Dose Estimates Based on the
LOD:

At least three methods have been used in
past epidemiologic studies to arrive at
notional dose estimates based on the LOD.
These include:

® LOD/2.”

® LOD/Vv2.*

® Maximum Likelihood estimation based
upon assumption of a lognormal
distribution of exposure
measurements."

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Nondetectable Workshop

dose) to be addressed so that future study
of working populations across several sites

can be accomplished.

Topics for future “Research Issues
Workshops” are listed below:

@ Issues relating to internal dosimetry and

it application to epidemiology.

Issues regarding energy level and
geometry factors, organ dose from both
internal and external exposures,
developing estimates of uncertainties
and identifying biases encountered in
dosimetry and risk estimation.

Issues related to the identification and
collection of historical records for use
in these studies.

Issues related to the effects of chemical
exposures.

Page 22


CDC

CENTERS FOR DISEASE CONTROL
‘AND PREVENTION

NIOSH

NIOSH
Research Issues Workshop:

Epidemiologic Use of
Nondetectable Values in
Radiation Exposure Measurements

Cincinnati, Ohio
September 9 and 10, 1993

s sees
S
f U.S DEPARTMENT OF HEALTH AND HUMAN SERVICES
= Public Health Service
“ay Centers for Disease Control and Prevention
vag National Institute for Occupational Safety and Health

NiosH 229647
wris- FB 9S 1B960f

a ge en ce a mar ana aman mane nearer a


Nondetectable Workshop

make the JEM approach unnecessary. In
all likelihood, the exposure monitoring
data used to derive exposure estimates for
the cells of the matrix will involve real
measurements (with an attributable
variation or uncertainty) plus missed dose,
left-censored and/or notional data. The
data used for each cell must be evaluated
for the proportional contribution of each
data type and a decision made regarding
the influence on the estimate. For
example, in a cell of a given matrix,

36 measurements are available for use to
derive an exposure estimate for the job title
Decontamination Technician, within the
Chemical Processing Department, in
Building 379, for the year 1964. Of the 36
measurements, 6 are reported as non-
detectable and would require one of the
previously described imputation strategies
to assign a number for each in order to
calculate a mean for the 36 data points.
This may be accomplished by examining
the distribution of the values in the data
set, or by assigning a number for

each censored data point using LOD/2 or
LOD/ v2. In some cases the amount of
non-detectable data used in deriving an
estimate for a cell will be minimal and
would not lead to misclassification of
exposure. In other cases, the available
data may require augmentation from
additional data sources, e.g., other area or
personnel monitoring data, to derive a
reasonable and defensible estimate.

Subsequent exposure monitoring may be
utilized to increase existing information,
derive an exposure assignment to fill an
empty cell, validate the historical
monitoring data used, or to enhance the
basis for a derived estimate. This
approach should only be applied in

situations where process operations and
exposure potentials have not substantially
changed over time. This approach may be
extremely beneficial where parameters of
increased sensitivity (lower detection
limit), improved specificity (reduced
interference), and accuracy of analytical
procedures are evident. With external
monitoring there was generally an
improvement in these parameters when the
period for wearing dosimeters was
increased.

Exposure assignment may be categorical or
quantitative in approach depending upon
the type, quality, and quantity of data used
to create the matrix. Exposure assignment
may:

@ be defined as "ever" versus "never"
exposed;

® be based on duration of exposure or
employment in a job title, department,
building location, i.e., categories such as
high, medium, low;

G consist of a semi-quantitative estimate of
exposure for broad work categories based
on analysis of exposure monitoring and
process data; or,

@ represent a quantitative estimate of
exposure for narrowly defined work
groupings based on detailed high-quality
exposure monitoring and process
information.

A matrix may be constructed using one of
these exposure assignments depending on
the quality and quantity of information
used. When feasible and appropriate, a
subset of data may be held in reserve and
used to test the validity of an exposure
assignment. Additionally, an expert panel



Nondetectable Workshop

where a JEM may be applicable. The
advantages of the JEM approach for
epidemiology are:

@ It is efficient to reconstruct average
dose/exposure histories for each
worker.

© Itcan supplement individual radiation
dose/exposure records whenever gaps
or censoring have been identified.

Reconstruction of exposure histories based
on a common experience avoids the need
to evaluate individual occupational dose
histories for each worker, thus making
efficient use of available resources. The
JEM can also be used to supplement
individual radiation exposure estimates
whenever gaps or censoring have been
identified. Unfortunately, throughout the
history of the DOE facilities, workers
regularly changed jobs and work locations
without a change in job classification or
title. Likewise, records of job title
changes may not be truly reflective of the
actual working conditions, since it was
believed that specific job activities could
provide information about the secret nature
of work being conducted at the DOE
facilities. Therefore, job titles and
descriptions were intentionally vague to
avoid the risk of releasing any information
that might be construed as a breach of
security. These practices make the JEM
more difficult to develop for epidemiologic
use.

Limitations in applying the JEM approach
to epidemiologic studies at DOE facilities
are:

@ Monitoring programs were
implemented to assure efficiency of

engineering control systems, not to
estimate exposures.

@ Many technological changes were being
implemented, affecting the accuracy of
the monitoring measurements.

Historically, air sampling programs were
not conducted to estimate worker
exposures but to check the operation of
engineering control systems, such as glove
boxes and other containment systems.
Therefore, many sampling locations were
placed in areas where abnormal conditions
would most likely occur. Usually these
locations were not representative of the
workers environment. In addition, the
location of samplers, the duration of
samples, airflow rates and sampling
frequency were not optimal for estimating
worker exposures. The measurement itself
was designed for a qualitative rather than a
quantitative indication of exposure. Also,
the specificity (knowing which
radionuclide was being measured) was not
a monitoring requirement.

During the 1940s and 1950s, significant
improvements in technology were being
implemented for both the personal and the
area monitoring programs. If a JEM were
to be developed using these data, certain
assumptions have to be made along with a
careful review of the production processes
and their related jobs.

Once developed, the matrix is used to
assign exposure estimates for agents of
interest: At DOE facilities the JEM
approach would be most useful for
estimating exposure to chemical agents and
perhaps internal radiation exposure.
Enough individual measurements generally
exist for external whole-body radiation to

Page 8



Nondetectable Workshop

variations thereof means that any result Following each presentation a brief
meeting this criteria are below some question and answer session was held to
threshold level. assure a basic understanding of the

presented material. Miscommunication
among scientists with different
backgrounds is not uncommon since much
of the same vocabulary may have different
meanings to each profession. For

The workshop attendees and speakers example, the word "valid" can be
represented several areas of expertise interpreted by health physicists to mean
including internal and external radiation that a result is true or accurate, but an
dosimetry, biostatistics, epidemiology, epidemiologist might interpret it to mean
health physics, industrial hygiene and that an approach is justified or acceptable.
tadiochemistry. Table 2, lists the
workshop attendees.
The presenters and respective
topics were: TABLE 2
a Workshop Attendees
Dr. Jim Ruttenber, Historic
uses of non-detectable data in oe SSS
epidemiology; Name Expertise Organization
Dr. Richard Hornung _Biostatistician NIOSH
Stor Dr. Anne Fidler Epidemiologist NIOSH
Mr. Herb Meyer, Historic Mr. Larry Elliott Industrial Hygienist NIOSH
ee Dr. Thurman Wenzl Industrial Hygienist NIOSH
monitoring methods; Dr. Steve Ahrenholz Industrial Hygienist NIOSH
Mr. Samuel Glover Health Physicist NIOSH
Mr. Bill Moss, Historic Mr. John Cardarelli Health Physicist NIOSH
overview of internal Dr. Henry Spitz Health Physicist NIOSH
monitoring methods Ms. Janice Watkins Biostatistician ORAU
(specifically plutonium Dr. Ethel Gilbert Biostatistician PNL
radiochemistry), Mr. Bill Tankersley © TH / HP ORAU
Mr. Hap West Health Physicist ORAU
Dr. Allen Brodsky, Detection Mr. Allen Beadsky He | Ra iochemistry CAN am
limit quandary and missed Dr. Daniel Strom Health Physicist PNL
dose concepts; Mr, Larry Tomezak _ Statistician FERMCO
Mr. Jack Fix Health Physicist PNL
Dr. Steve Wing, External . Mr. Herb Meyer Health Physicist Mound / Retired
Exposures at ORNL and their Dr. Jim Ruttenber Epidemiologist Univ. Colorado
Implications for Epidemiology Dr. Steve Wing Epidemiologist Univ. N. Carolina
Dr. Ed Frome Biostatistician ORAU
em <<
Dr. Ed Frome, One
solution/approach used on an
Oak Ridge cohort.

Page 5


Nondetectable Workshop

Ed Frome from ORNL and several
representatives of ORISE (Bill Tankersley,
Janice Watkins, Hap West) described an
approach used to adjust cumulative dose
estimates at the facility in Oak Ridge.
They determined that the general practice
at ORNL between 1944 and 1956, was to
read badges on a weekly basis.% Results
below the limit of detection (about

0.3 mSv during this period) were recorded
as zero. They assumed that some of the
annual recorded zeros actually represented
true zero exposures above background,
while others were an underestimate of true
low-level positive doses. They identified
true zeros by the following criteria:

© Workers employed for five or more
years with all zero readings.
and
© The department in which a person
worked most frequently had 75% or
more zero readings.

All the other annual readings were adjusted
upward by an algorithm developed from a
sample of several hundred hard copy
records which contained both film badge
and pocket meter readings. For each week
that the shielded film badge was recorded
as zero but where weekly pocket meter
readings were available, the pocket meter
readings were summed to estimate the dose
missed by badges during the year. A least
squares regression was applied to these
data to develop a prediction equation for
the amount of upward adjustment as a
function of the unadjusted annual recorded
doses for all workers with recorded annual

doses below 16 mSv. All workers above
16 mSv were given an extra 3 mSv. Use
of this algorithm resulted in a mean
increase of approximately 5 mSv per year
before 1956. Additional details of this
approach are provided in a technical
report.”

Dr. Frome suggested an alternative
approach to account for both uncertainty
and bias in the dose measurement.” The
estimated dose could be treated as a
probability distribution developed from all
the historical data recorded for an
individual during the year. This method
based upon Bayesian statistics requires
knowledge and/or assumptions regarding
the true performance of the dosimeter.
Complicating the development of these
probability distributions with time are the
same problems encountered with other
methods of retrospective dose assessment:
the changes in dose measurement
techniques, dosimetry monitoring
programs, and recording practices. In
order to estimate the true distribution of
doses over a period of time (known as the
prior distribution in Bayesian analysis)
weekly pocket meter readings were used.
This approach results in an adjusted dose
distribution for a specified period of time
that can be used to reassign person-years in
an epidemiologic study to the adjusted dose
intervals. Frome concluded that the
adjusted dose distributions were almost
always centered above the recorded dose
distributions. In some cases there was
severe underestimation of true dose using
the recorded data. The degree of
underestimation was proportional to the
number of recorded zero weekly film
badge readings. This approach is
considerably more complex than the

Page 19



Nondetectable Workshop

10.

11.

12.

References

Office of Technology Assessment, Complex Cleanup: The Environmental Legacy of
Nuclear Weapons Production, OTA-O-484 Washington, D.C.: U.S. Government Printing
Office, February 1991.

Tankersley WG, et al. Assessment of Radiation Exposures at or Below the Minimum
Detectable Level in Epidemiologic Studies. Center for Epidemiologic Research, Oak
Ridge Associated Universities, Department of Environmental Sciences and
Engineering, University of North Carolina at Chapel Hill.

Brodsky A. Detection Limit Quandary and Missed Dose Concepts. Workshop
Presentation Material, 1993.

Strom JS. Estimating Individual and Collective Doses to Groups with ‘Less Than
Detectable’ Doses: A methods for use in epidemiologic studies. Health Phys, 51, 437-
445, 1986.

Hornung RW and Reed LD. Estimation of Average Concentration in the Presence of
Nondetectable Values. Appl. Occup. Env. Hyg., January 1990.

Atwood CL, et al. Recommended Methods for Statistical Analysis of Data Containing
Less-Than-Detectable Measurements. Idaho National Engineering Laboratory,
EGG-SARE-9247, Rev. 1., 1991.

Waite DA. Interpretation of Environmental Radioactivity Measurements. CRC
Handbook of Environmental Radiation. pp. 173-182, 1982.

Armstrong BG. Confidence Intervals for Arithmetic Means of Lognormally
Distributed Exposures. Amer. Ind. Hyg. Assoc. J.. 53(8):481-485, 1992.

Nielson KK, and Rogers VC. Statistical Estimation of Analytical Data Distributions
and Censored Measurements. Anal. Chem., 61, (24), 1989.

Nehls GJ, and Akland GG. Procedures for Handling Aerometric Data. J. Air Pollut.
Control Assoc. 23:180, 1973.

Hald A. Statistical Theory with Engineering Applications. John Wiley and Sons, Inc.,
New York, pp. 144-151, 1952.

Job exposure matrices. Proceedings of a Conference held in April 1982 at the
University of Southampton. Scientific Report No. 2., Medical Research Council,
Environmental Epidemiology Unit, 1983.

Page 25



Nondetectable Workshop

The Health-Related Energy Research
Branch of the National Institute for
Occupational Safety and Health (NIOSH)
heid the first of several planned workshops
to determine the optimal use of current and
historical exposure/dose data for use in
epidemiological studies of radiation-
exposed workers. The participants in this
workshop examined procedures for
interpreting nondetectable and erroneous
values in occupational radiation exposure
records. Presentations by invited speakers
provided a basis for discussing methods for
interpreting results from radiation
dosimeter and bioassay measurements
which were recorded as zero or adjusted in
some manner by past administrative
practices. Changes in interpretation and
definitions for detection limit have an
impact on the manner in which results
were recorded and how they should be
interpreted for epidemiologic purposes.
Also, personnel dosimetry methods and
procedures at Department of Energy
facilities have changed significantly over
time with the improvement in radiation
measurement technology. Likewise,
changes in record keeping procedures
necessitate that special methods be
developed for interpreting nondetectable
results. Pocket ionization chamber
measurements were suggested as one
method for supplementing historical results
of film dosimeters. Other proposed
methods included the use of probability
distributions and Bayesian statistics to
estimate the frequency with which results
would occur below the administrative limit
or minimum detectable dose. This
workshop provided an opportunity to

review past health physics dosimetry
measurement and record keeping practices
and to discuss new methods for interpreting
historical measurements for use in
epidemiologic studies. Several
recommendations were made for topics for
future workshops.

During World War II the top secret
Manhattan Project combined the nation's
most elite scientists with military leaders to
produce the first atomic bomb.
Development of this nuclear device
required an enormous amount of resources
as well as scientific and technical efforts.
Thousands of square miles spread across
thirteen states served as principal
development and production sites, making
this effort a success in terms of national
security. These sites are referred to as the
Weapons Complex, employing over a half
a million workers since the mid 1900s.
Many of these facilities were involved in
several operations including weapons
research and development, nuclear
materials productions, warhead component
production, warhead testing and waste
disposal, (see Table 1).'

Although these facilities have much in
common, there is no "typical" facility with
regard to exposure potential. Each site has
a unique combination of hazards that shape
its particular exposure problems.
Exposures to both chemical and physical
agents occur at most facilities, but the type
and degree of exposures have varied over
time and from site to site. Practices for
reporting occupational exposures have also

Page 1



Nondetectable Workshop

The first limitation introduces a potential
problem for epidemiology if a site has
processes where neutrons or “soft” betas
are present. X-rays or gammas between
40 keV and 1 MeV and "hard" betas above
1 MeV are measured with an accuracy
+/-15%. Specially, designed PICs with
boron impregnated within the chamber may
have been used for neutron detection, but
were not discussed. The limited energy
range of these instruments could cause the
cumulative external exposures to be
underestimated. In addition, their energy
dependence, which has not been studied:
could be a bias in the exposure assessment.

Another limitation of the PIC is its
physical sensitivity. A discharge (or high
reading) can be induced by physical shock,
such as dropping the PIC, excessive
humidity, or dirt on the electrical
connections. Physical design
characteristics allow the PICs to potentially
produce false-positive readings but never a
false-negative reading. Thus, they were
issued to workers in pairs and the lower of
the two readings was recorded as the
official exposure. The higher reading
would be considered a false positive due to
"leakage" or some other physical
deficiency. If false-positives are
incorrectly used in the cumulative estimate,
an overestimate of the exposure would
occur. The effects of energy dependence
and false-positives may negate their overall
bias’ in an epidemiologic study. However,
this has not been studied.

Film Badge Dosimeters:
The early dosimeters used at DOE

facilities, see Figure 2, were adopted from
those developed at Oak Ridge, Los

Alamos, and Hanford, since the
measurement technology was developed in
cooperation with these facilities in the early
history of the Manhattan Project. The lead
laboratory in the design of the film
dosimeter was the University of Chicago as
described in report CH-1553 dated
4/8/1944.

Each DOE facility modified the original
design of the film dosimeter to suit their
individual needs because radiation fields
and radioactive materials encountered at
each site were unique. The first personnel
radiation dosimeters used on a routine basis
consisted of at least one piece of duPont
type 502 and/or 510 x-ray photographic
film plus a set of absorbers or shields to
help characterize the radiation. The
absorbers included several different types
of metals including cadmium, lead, brass,
and tin. Areas behind these absorbers are
commonly referred to as the “closed
window" or "deep" doses. The film
dosimeter casing was also designed so that
a portion of the film would have no
absorber, referred to as an “open window"
or "shallow" dose, detecting primarily beta
particles. The resulting beta and gamma
exposures were determined by an algorithm
that was developed from the. calibration
procedure.

Special case - neutron dosimetry:

Nuclear Track Emulsion (NTA) films

were used for neutron dosimetry starting in
the late 1940s. Although the film was
processed in a manner similar to that

for the gamma radiation dosimeter, neutron
tracks rather than film darkening were
measured. The weekly “tolerance limit”
for neutron exposure was 150

Page 12



Nondetectable Workshop

e Permanent record which could be re-
read if available.

@ Measures a wider range of photon and
beta energies than PICs.

@ Measure neutrons with greater accuracy
than PICs.

© Less susceptible to interpretational
error than PICs.

Film badges, like PICs, also provide
individual specific exposure information.
A major advantage of the film badge is the
ability to go into the archived records and
re-read a sample of the old film badge
results. This permanent record of dose
allows historical data to be verified and
checked for accuracy. This option has its
limitations though, available historical
calibration curves, adverse storage
conditions, poor film integrity, and fading
of the films all pose significant problems to
successfully re-reading old film badges.'*"’

There are other options that can be
considered prior to re-reading all the
badges. One would be to obtain an
important piece of information that must be
included with the original film, the data
processing sheets. These data sheets show
the optical density observed with each
personnel film along with the associated
calibration results. If these records are
available, it would be much simpler to
review these for accuracy than attempting
to re-read the original film.

Other advantages of the film badges are a
wider response to photon, beta and neutron
energies and they are less susceptible to
interpretational error, resulting in a truer
measure of external exposure than the
PICs.

Limitations:

While film badge results make up the
majority of historical external dosimetry
information used in epidemiology, several
limitations need to be considered prior to
applying the data to an epidemiologic
analysis:

e Higher limit of detection (around
0.30 mSy).

@ More results fall below the LOD with
higher sampling frequency.

© Responses at low energies (< 100 keV)
were exaggerated.

®@ Units of measurement have changed.

© Training and intensive work are
required to determine neutron
exposures.

The film badge typically had a LOD of
about 0.2 to 0.4 mSv (20-40 mrem)
compared to about 0.02 mSv (2 mrem) for
the PIC. Historically, some records show
recorded external dose from a film badge
as low as 0.1 mSv (10 mrem), but these
values are considered highly uncertain by
the site health physicists. A 0.2 mSv
LOD would not pose a significant problem
as long as the exposure time was
significantly long enough to have received
at least 0.2 mSv. However, this was often
not the case at these DOE facilities. The
frequency of dosimeter change out
occurred on a weekly, monthly, quarterly,
or sometimes on a semi-annual basis.
Weekly change outs occurred most often in
the earlier years creating the greatest
potential for a missed dose. The missed
dose concept will be addressed later in this
paper. However, it is important to note
that this concept can adversely affect
epidemiologic evaluations for calculating

Page 14



Abstract... 0c cee tenet rete ere e eens sess s es 1
Background .. 2.0.0. cece eee t retest seers sss s sss 1
Introduction 2.0... - eee ce eect teeter eters neers rss eres 3
Objective 60.0... e eee ete eee tte e teeter ners errr s ess 3
Workshop Issues... ee ee eee eet rete ert teers rss sss 4

External Exposure Data ....

Internal Exposure Data 4
Arrangement of Workshop ....---- 0 se sere errr eet rtt nett rse rests ess 4
Workshop Attendees and Speakers .... 2... - +22 esse reer rte rrr ssressss 5
Historic Uses of Non-Detectable Data in Epidemiology ....-. +--+ +++ sere rrtrte 6
Missing Dose Data ....-.----e eee er eres 6
Doses Below the Limit of Detection: ....-.-+-+-+++e0> .. 6
Notional Dose Estimates Based on the LOD 6
Alternative Methods for Handling Missed Dose, and Censored and Notional Data
cee eee cee eee eee eee ee eee terete eee eee eee eee 7
Workshop Discussion: Epidemiologic Uses of Non-detectable Values; JEM ..... 7
Historic Overview of External Monitoring Methods ....-.-- +--+ seer er rercres 10
Pocket Ion Chamber (PIC) .... 0... eee cece eer ere rete rtntt 10
Film Badge Dosimeters ......---- e+ -e eres 12
Special case - neutron dosimetry ....--++--++++ 12
Workshop Discussion: External Dosimetry Issues 15
Historic Overview of Internal Monitoring Methods ......- +. ++ se ee rectrrrcte 17
Detection Limit Quandary and Missed Dose Concepts 17
\ Resources useful in defining limits of detection i7
} Sources and magnitudes of errors in dosimetry 17
; External Exposures at ORNL and Their Implications for Epidemiology: .....---+-- 18
One Solution/Approach Used on a Oak Ridge Cohort «00.0... 22 222225 e rere 19
Workshop Discussion: Use of PIC Data in Epidemiology ......-+-++++-+0° 20

Recommendations ......--. 02 e ee eee etter rete terest 21



Nondetectable Workshop

APPENDIX A

Below Detection Limit References
Compiled by DJ Strom and HR Pritchard, rev. July 28, 1992

Atwood CL, Blackwood LG, Harris GA, Loehr CA. Recommended Methods for Statistical
Analysis of Data Containing Less-than-Detectable Measurements. Springfield, VA: National
Technical Information Service; EGG-SARE-9247, Rev.1; 1991.

Finkel, AM. A Simple Formula for Calculating the "Mass Density" of a Lognormally
Distributed Characteristic: Applications to Risk Analysis. Risk Analysis 10(2):291-301, 1990.

Gilbert RO, Kinnison RR. Statistical Methods for Estimating the Mean and Variance from
Radionuclide Data Sets Containing Negative, Unreported or Less-than Values. Health Phys.
40:377-390, 1981.

Helsel DR. Less Than Obvious: Statistical Treatment of Data Below the Detection Limit.
Environ. Sci. Technol. 24(12):1766-1774, 1990.

Hertzler CL, Atwood CL, Harris GA. Current Methods of Handling Less-Than-Detectable
Measurements and Detection Limits in Statistical Analysis of Environmental Data. Idaho
Falls, ID: Idaho National Engineering Laboratory; EGG-SARE-8609; 1989.

Hornung R, Reed LD. Estimation of Average Concentration in the Presence of
Nondetectable Values. Appl. Occup. Environ. Hyg. 5(1):46-51, 1990.

Newman MC, Dixon PM. UNCENSOR: A Program to Estimate Means and Standard
Deviations for Data Sets with Below Detection Limit Observations. Amer.Environ. Lab., Apr
il, 1990.

Newman MC, Dixon PM, Looney BB, Pinder III JE. Estimating Mean and Variance for
Environmental Samples with Below Detection Limit Observations. Water Resources Bulletin
25(4): 905-916, 1989.

Neilson KK, Rogers VC. Statistical Estimation of Analytical Data Distributions and Censored
Measurements. Anal. Chem. 61:2719-2724, 1989.

Rappaport SM, Selvin S. A Method for Estimating the Mean from a Lognormal Distribution.
Amer. Ind. Hyg. Assoc. J. 48(4):374-389, 1987.

Selvin S, Rappaport S, Spear R, Schulman J, Francis M. A Note on the Assessment of
Exposure Using One-Sided Tolerance Limits. Amer. Ind. Hyg. Assoc. J. 48(2):89-93, 1987.

Page 23



ACKNOWLEGDEMENTS

These proceedings were compiled by the efforts of the following participants:
John Cardarelli II

Henry Spitz
Larry Elliott

Mention of the name of any company or product does not constitute endorsement by the
National Institute for Occupational Safety and Health.

— — = — ———= — —
This document is in the public domain and may be freely copied or reprinted, |

— — — — — — —— — —_

Copies of this document are available from:

Health-Related Energy Research Branch, DSHEFS
National Institute for Occupational Safety and Health
4676 Columbia Parkway

Cincinnati, Ohio 45226

(513) 841-4470 (facsimile)

(513) 841-4400 (phone)

For information on other occupational safety and health problems, call 1-800-35-NIOSH.



iq
i
|
|

Nondetectable Workshop

13.

14.

14.

16.

17.

18.

19.

20.

21.

23.

Wilson RH, Baumgartner WV, Fix JJ, and Nichols LL. Description and Evaluation of
the Hanford Personnel Dosimeter Program from 1944 to 1989. Technical Report PNL-
7447, Pacific Northwest Laboratory, Richland, WA, 1990.

Brodsky A. and Kathren RL. Accuracy and Sensitivity of Film Measurements of
Gamma Radiation. Part 1, Comparison of Multiple Film and Single Quarterly-Film
Measurements of Gamma Dose at Several Environmental Conditions, Health Phys., (9)
453-462, 1963. :

Brodsky A, and Kathren RL. Accuracy and Sensitivity of Film Measurements of
Gamma Radiation. Part II, Limits of Sensitivity and Precision, Health Phys.,
(9) 769-777, 1963. :

Correspondence. Bigler WA and Phillabaum GL, "Records of External Dosimetry
Results - Other DOE Sites,” Monsanto Research Corporation, Health Physics
Operations T-313, May 1978.

Watkins JP, et al. Adjusting External Doses from the ORNL and Y-12 Facilities for the
Oak Ridge Nuclear Facilities Mortality Study. ORISE Technical Report #941G-34,
1994.

Gilbert ES. Accounting for Bias and Uncertainty Resulting from Dose Measurement
Errors and Other Factors. Technical Report PNL-SA-18907, Pacific Northwest
Laboratory, Richland, WA 99532, 1990.

Hart JC. A Progress Report Dealing with the Derivation of Dose Data from ORNL
Personne! Records Applicable to the Mancuso Study. Technical Report ORNL/M-2614
(formerly, ORNL CFM 66-1-84), Oak Ridge National Laboratory, Oak Ridge, TN,
37831, 1966.

Taylor NA. Estimation of Dose Received when Dosimeter Results are Recorded Below
a Threshold Level. J. Radiol. Prot., 11(3):191-198, 1991.

Currie LA. Limits of Qualitative Detection and Quantitative Determination. Anal.
Chem., 40, (3), 586-593, 1968.

American National Standard Institute (ANSI), Performance Criteria for Radiobioassay.
ANSI N13.30 standard. New York, NY: ANSI 1989.

Brodsky A. "Accuracy and Detection Limits for Bioassay Measurements in Radiation
Protection -- Statistical Considerations, " NUREG-1156, April 1986.

Page 26



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Nondetectable Workshop

could be convened to review and evaluate
the validity of exposure assignments.

Historic Overview of External
Monitoring Methods: Herb Meyer

Mr. Meyer, former manager of Health
Physics for Monsanto Research
Corporation at the DOE Mound Plant,
described the historical DOE external
dosimetry program involving the use of
pocket ion chambers and film dosimeters
as the methods for monitoring external
radiation exposure. Neutron dosimetry
using film badges is also discussed.
Finally, the discussion session summarizes
contributions from members of the meeting
who provided additional insight to the
historical external dosimetry practices at
the DOE.

Pocket fon Chamber (PIC):

A pocket ion chamber, see Figure 1, is
essentially a capacitor which holds about
150 volts. Photon interactions in the wall
of the PIC discharge the capacitor. The
amount of discharge is related to the
exposure received by the individual. PICs
were used as the official record of external
exposures to ionizing radiation until about
1944, when Hanford Engineering Works
made film badges the official record.”
Prior to 1944, they were routinely (daily)
used to assure a workers exposure was
within the radiological limits.

Advantages:
Although PICs proved to be a useful

instrument for compliance purposes, their
usefulness for epidemiologic studies is

still to be determined. Several

“epidemiologic” advantages for using PIC

exposure data are:

e PIC data provide individual exposure
information.

@ Frequent monitoring results are
available (often daily).

e Lower limit of detection than film
badges

e PIC exposure data exist in historical
documents.

Having individual exposure data is ideal
for conducting epidemiologic studies, and
the PIC data provide this type of
information. Daily monitoring of the
workers' activities is also very useful,
especially in the exposure assessment
portion of a study. For example,
combining an individual's exposure history
with his work activities/responsibilities can
help estimate a co-worker's exposure that
is missing. PIC data also provide critical
information that may be used to build a
JEM for a group exposure. Another
advantage is that the PICs have lower
LODs (about 0.02 mSv) than the film

badge (about 0.3 mSv) and is easier to read
at the lower ranges. Historically, during
read-out the spacing between numbers was
further apart at the lower exposures and
was closer together at the higher
exposures, making the Jower exposures
easier to read. Finally, historical PIC
records exist at these facilities and can be
utilized for future studies. However, the
magnitude of this type of task could be
quite large and expensive. Its important to
consider the cost effectiveness before

ing any steps to improving the exposure
data.

Page 10

———————— CS


Nondetectable Workshop wath

Figure 2
Historic Film Badge

aun 10 (2
=
& 7
Z
ncutnon Fis (>

neutrons/cm?-sec which is equivalent to Advantages:
approximately 300 mrep (roentgen

| equivalent physical). Eventually, the Beginning as early as 1944, doses

| weekly tolerance limit was reduced in determined from film badges became the
stages to 30 neutrons/cm’-sec in 1956. official record for compliance reporting,
Unfortunately, historical occupational replacing the PICs. Therefore, most of the
radiation exposure records at several DOE historical exposure data used in
facilities recorded the neutron dose as a epidemiology today is in this form. The
multiple of the tolerance limit, making a advantages of using film badge data in
dose adjustment more difficult. Exposure epidemiologic studies are:
assessment strategies must take into
account these factors to assign appropriate © Individual exposure information.

dose estimates for epidemiologic studies.

Page 13