ORAU Team

Dose Reconstruction Project for NIOSH

Technical Information Bulletin – Analysis of Coworker 

Bioassay Data for Internal Dose Assignment

Document Number:

ORAUT-OTIB-0019 

Effective Date: 12/29/2004

Revision No.: 00

Controlled Copy No.: ______

Page 1 of 6

Subject Expert: Elizabeth M. Brackett

Document Owner

Approval: Signature on File Date: 12/09/2004

Judson L. Kenoyer, Task 3 Manager

Concurrence: Signature on File Date: 12/09/2004

Richard E. Toohey, Project Director

Approval: Signature on File Date: 12/29/2004

James W. Neton, Associate Director for Science

Supersedes:

None
Effective Date: 12/29/2004 Revision No. 00 Document No. ORAUT-OTIB-0019 Page 2 of 6

RECORD OF ISSUE/REVISIONS

ISSUE 

AUTHORIZATION 

DATE

EFFECTIVE 

DATE

REV. 

NO. DESCRIPTION

Draft 11/10/2004 00-A New technical information bulletin for the analysis 

of coworker bioassay data for internal dose 

assignment. Initiated by Elizabeth M. Brackett.

Draft 11/18/2004 00-B Incorporates internal review comments. Initiated 

by Elizabeth M. Brackett.

12/29/2004 12/29/2004 00 First approved issue. Initiated by Elizabeth M. 

Brackett.
Effective Date: 12/29/2004 Revision No. 00 Document No. ORAUT-OTIB-0019 Page 3 of 6

1.0

This document assigns responsibility for and guidance on the analysis of coworker internal dosimetry 

data for the purpose of assigning doses to unmonitored or partially monitored workers. The general 

approach outlined herein is to be used, but the specific details are guidance rather than requirements. 

Deviation from the guidance could be necessary because the dosimetry data sets will have unique 

characteristics based on facility procedures, periods of monitoring, and other factors. Deviations from 

the guidance must be documented. 

PURPOSE

2.0

This method assumes that the dosimetry results for groups of workers are lognormally distributed. 

Studies of worker dosimetry results (bioassay results, dosimeter results, etc.) tend to support this 

assumption. Alternate distributions can be used if the data for a particular set do not appear to be 

lognormally distributed. 

BACKGROUND

In general, dosimetry is associated with workers who have the largest potential for exposure. While 

there can be exceptions to this such as accidents, it remains very unlikely that any unmonitored 

worker received a dose greater than the most exposed monitored worker at a site.

The 50th-percentile (median) result and the 84th-percentile result are calculated for the data set on a 

monthly basis where there are adequate results. The period could need to be lengthened where the 

data sets are small or sporadic. For internal dose, intake rates must be determined from the 

calculated bioassay distributions. The geometric standard deviation (GSD) is calculated by dividing 

the 84th percentile by the 50th percentile. 

This method avoids the need to define the minimum detectable activity or amount (MDA) for 

uncensored data sets. In addition, the method eliminates the need to remove what could appear to 

be unreasonable outliers because the data distribution is evaluated rather than the individual datum. 

3.0

Figure 1 shows the process flow of the following responsibilities:

RESPONSIBILITIES AND FLOW OF INFORMATION 

Team Leader

Responsible for coordinating all aspects of the process for a given site. Ensures that each identified 

party has required information and maintains schedules.

Obtains information or answers in response to questions identified by the SME. 

Compiles all information, including the following details, into the appropriate site technical basis 

document (TBD). 

• Documents intake periods and intake rates of primary (monitored) radionuclides and 

associated absorption types. 

• If appropriate, documents radionuclides associated with the primary radionuclides that should 

be included in intake calculations. The associated radionuclides and their relative activities 

should be specified. 
Effective Date: 12/29/2004 Revision No. 00 Document No. ORAUT-OTIB-0019 Page 4 of 6

Task 1

Obtains identified dosimetry data sets and makes them available, in a database with query ability, to 

individuals who review or analyze the data.

Subject Matter Expert (SME)

Reviews the data sets to determine completeness and usability and to identify shortcomings. 

Determines which data sets are useful for assigning coworker doses and, for sites with several 

methods of monitoring (e.g., urine and lung counting), determines which method to use to assign best 

estimates of dose and which data are to be used to verify reasonableness.

Documents information required for proceeding with data analysis to be turned over to the Team 

Leader for investigation and resolution. Information that could be needed for a given site includes:

• Interpretation of bioassay results (e.g., units, period of collection, and codes).

• Unmonitored radionuclides in the source term (e.g., specific ratios of plutonium, neptunium, 

and technetium contaminants in recycled uranium).

• Appropriate assumed intake periods (i.e., for missing periods in the data, determine if there 

should have been monitoring or if there was no potential for intakes).

• Conversion of results from mass to activity units.

• Identification of “positive” results, if results are listed as less than the MDA or if the data are 

incomplete. 

Determines periods for analyzing the data (e.g., monthly or quarterly). This is a matter of judgment 

that includes consideration of the monitoring frequency and the amount of available data.

Addresses any data adjustments (e.g., normalization of bioassay results to 24-hour sample period, 

recovery efficiency) needed before data analysis can be performed. 

Data Statistics Analyzer

If any anomalies are found in the data, contacts the Team Leader and explains the situation. After 

reviewing the data and the anomalies, and based on professional judgment, the Team Leader and 

SME may recommend deviations from the data analysis instructions. Deviations and their bases must

be documented. 

Analyzes the data:

Sorts data for each identified period (e.g., month or quarter) from low to high results and ranks the 

data. All data are to be included in the ranking.

Calculates the percentile midpoint represented by the rank. 

Log-transforms the data. 

Calculates the z-score of each percentile. 

Plots the z-scores versus the natural logarithms of their respective data (this step is optional).
Effective Date: 12/29/2004 Revision No. 00 Document No. ORAUT-OTIB-0019 Page 5 of 6

Uses the z-scores and associated natural logarithms of the data to determine a line equation and 

the associated fit parameter, R2

. (R2 > 0.9 indicates a reasonable fit.) The line equation is

y = mx + b 

where

y = natural logarithm of the data 

m = slope of the line

x = z-score

b = y-intercept

Note: Results with values less than or equal to 0, as well as results recorded as less than MDA, 

where MDA can be a numeric value or the letters MDA, are excluded from the line fit.

Calculates the 50th percentile, the GSD, and the 84th percentile for each period of dosimetry data: 

50th percentile = eb

GSD = em

84th percentile = em ∗ eb

Provides the resultant values to the SME in a columnar format suitable for pasting into IMBA. 

Columns contain the period of the data, an effective bioassay date, the 50th-percentile values, and 

the 84th-percentile values. 

Modeler

Determines intake rates by performing fits of the two data bioassay data sets (50th- and 

84th-percentile results) associated with each radionuclide.

• For most data sets, intakes will be assumed to be chronic. There could be large, short-term 

releases that need to be addressed individually.

• Uses site information (e.g., dates of shutdowns; known operating periods), where possible, to 

break the chronic intake into periods. These periods should be adjusted as necessary to 

obtain a reasonable fit but assumed intake periods should not be very small. 

• Assesses intakes for each of the absorption types associated with a given facility. Documents 

intake regimes and rationale for fits.

Provides intake rates and periods, with documentation, including rationale for intake periods, to the 

Team Leader.

Tool Development Group

Develops tools to determine organ doses in accordance with the TBD. 
Effective Date: 12/29/2004 Revision No. 00 Document No. ORAUT-OTIB-0019 Page 6 of 6

Figure 1: Process Flow