DISCLAIMER: This is a working document provided by the Centers for Disease Control and Prevention (CDC) 

technical support contractor, SC&A for use in discussions with the National Institute for Occupational Safety and 

Health (NIOSH) and the Advisory Board on Radiation and Worker Health (ABRWH), including its Working Groups or 

Subcommittees. Documents produced by SC&A, such as memorandum, white paper, draft or working documents are 

not final NIOSH or ABRWH products or positions, unless specifically marked as such. This document prepared by 

SC&A represents its preliminary evaluation on technical issues.

NOTICE: This document has been reviewed to identify and redact any information that is protected by the 

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Memorandum

To: Subcommittee for Procedure Reviews

From: SC&A, Inc.

Date: September 9, 2022 

Subject: DCAS-PER-049 Subtask 4 – Internal Dose Followup

At the August 18, 2022, meeting of the Advisory Board on Radiation and Worker Health, SC&A 

presented its subtask 4 case review for DCAS-PER-049, “Paducah Gaseous Diffusion Plant.” 

Although SC&A’s review only evaluated external and occupational medical doses that were 

impacted by PER-049, SC&A did point out that the internal dose significantly increased. The 

increase in dose is questionable because the original dose reconstruction (DR) assigned 

hypothetical internal dose, while the rework used the energy employee’s (EE’s) bioassay data. 

During the meeting, the Board ask SC&A to evaluate the internal dose in more detail and report 

its findings to the Subcommittee for Procedure Reviews (SCPR). This memo provides a 

chronology of events and a summary of the internal dose calculations.

Chronology of DCAS-PER-049 Subtask 4 Review

• August 5, 2016: NIOSH issued DCAS-PER-049. 

• March 2, 2018: SC&A submitted its review of one case under subtask 4. SC&A had 

reviewed the Paducah Gaseous Diffusion Plant (PGDP) technical basis document (TBD) 

separately in 2006, and the 25 findings were resolved under the Gaseous Diffusion Plant 

Work Group. 

• October 31, 2018: SC&A presented its subtask 4 review of PER-049 to the SCPR. There 

were no findings, and the SCPR closed the review. 

Followup Discussion about Internal Dose

March 6, 2018. After receiving and reviewing SC&A’s PER-049, subtask 4 report, the 

Designated Federal Official (DFO) sent the following email to SC&A:

I’m curious. You reported that the “hypothetical” intakes originally estimated for 

internal doses were only about half of the actual internal doses estimated using the 

EEs bioassay records. I recognize this wasn’t part of your tasking but do you 

know the basis for the hypothetical intakes? I assume the bioassays weren’t 

captured at the time of the early DR but my question is whether there is anything 

to be learned from the original approach, whatever it was, to reduce the likelihood 
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PER-049 Internal Dose Followup, page 2 September 9, 2022 

NOTICE: This document has been reviewed to identify and redact any information that is protected by the 

Privacy Act 5 U.S.C. § 552a and has been cleared for distribution.

of underestimating should there be similar circumstances (the limited data 

available at the time of the original dose reconstruction) at other sites. 

I’m not asking you to do any digging on this at the moment, if you don’t know 

about the original basis. In that case, I’ll raise the issue directly with DCAS as it 

seems to me it could have some importance. 

March 6, 2018. SC&A responded to the DFO’s email as follows:

In the original 2005 DR it was stated (pages 5 and 6): 

Internal dose monitoring records were reviewed. Most measurement results for 

non-naturally occurring radionuclides showed an activity less than the level of 

detection for the given radionuclides and bioassay method. However, to account 

for any incidental dose that may have been received but not documented, internal 

dose was assigned based on a hypothetical intake assuming an intake of 

28 radionuclides. This results in an intake that greatly exceeds any possible actual 

intake by [the EE] because these nuclides would not all be found in a single 

location on site. The total internal dose assigned was 18.332 rem. 

[The EE] was monitored routinely during [the EE’s] career. Several urinalysis 

results were slightly above the minimum detectable values provided in PGDP 

internal dose TBD. An evaluation of the measurements that were above the level 

of detection was made for this dose reconstruction by comparing the bioassay 

results against the predicted results of the data provided in the Maximum Internal 

Dose Estimates for Certain DOE Complex Claims [NIOSH, 2004] The internal 

dose assigned based on the hypothetical intake is significantly higher than if the 

highest urinalysis result in [the EE’s] records was assumed to apply to a chronic 

intake over the entire employment period. This methodology applies and is 

considered claimant-favorable. . . . 

In the reworked 2016 DR it was stated (pages 8 and 9): 

Internal dose monitoring records were reviewed and it was determined that [the 

EE] was monitored for internal dose via [the EE’s] participation in the in vitro and 

in vivo bioassay programs in place at the Paducah Gaseous Diffusion Plant. [The 

EE] submitted several urine samples that were analyzed 

for total uranium concentration.

 Fitted and missed internal doses were calculated in 

accordance with the Technical Information Bulletin: Internal Dose Reconstruction 

. . . and the Technical Basis Document for the Paducah Gaseous Diffusion Plant – 

Occupational Internal Dose. . . . 

The total internal dose assigned was rem. 

The internal dose assigned to the in this dose reconstruction represents an 

increase from that assigned previously. This is due to the approach used in this 
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PER-049 Internal Dose Followup, page 3 September 9, 2022 

NOTICE: This document has been reviewed to identify and redact any information that is protected by the 

Privacy Act 5 U.S.C. § 552a and has been cleared for distribution.

dose reconstruction (a reasonable overestimate) as compared to the maximizing 

approach used in the previous dose reconstruction. Previously, the dose was based 

on hypothetical intakes. As stated above, the internal dose assigned in this dose 

reconstruction used [the EE’s] bioassay data, which presents a claimant-favorable 

estimate which more closely approaches the true internal dose received by [the 

EE].

There appears to be a contradiction between the two DRs concerning which is the 

larger dose resulting from the two internal dose methods (hypothetical or 

bioassay), that could use NIOSH’s clarification. I checked NOCTS for this EE 

and only a few external dose docs were added since the original 2005 DR, no 

additional internal data. I noticed this issue during in my evaluation but only 

briefly mentioned it in my report because of being tasked with a focus external 

dose review per PER-049, which did not include internal dose. For SC&A to 

investigate it further would require analyzing the info from the related OTIBs and 

TBDs used in the DRs and the IMBA files, etc.

March 7, 2018. The DFO sent the following email to NIOSH:

Would you please take a look (or have someone else take a look) at this DR and 

clarify what transpired to result in the original intended overestimate of the 

internal dose being only about half of the actual dose based on bioassays, as 

determined in the redone DR. Just want to make sure there isn’t a problem with 

the earlier method that might apply to other cases (for which bioassay is NOT 

available) at this site or at other sites. I recognize the first DR for this case was 

early on, so maybe whatever the problem might be, it is long ago resolved. I’ve

attached the SC&A PER Review report so you can identify the case. (SC&A 

wasn’t tasked with addressing the internal dose procedure, which wasn’t subject 

to the PER being reviewed.) 

SC&A is unaware of the outcome of this email or whether NIOSH provided a followup. 

ORAUT-OTIB-0002, Maximum Internal Dose Estimates for Certain DOE Complex 

Claims

In the original DR, NIOSH used ORAUT-OTIB-0002, revision 01 PC-2 (NIOSH, 2004; 

“OTIB-0002”), to assess the hypothetical internal dose for the PER-049 case. A summary of the 

OTIB-0002 sections relevant to internal dose follows. It should be noted that OTIB-0002 has 

been canceled. The date of cancellation approval is unknown to SC&A. 

OTIB-0002 application

OTIB-0002, section 2.0, “Background,” states the following: 

In accordance with OCAS-IG-002 (Internal Dose Reconstruction Implementation 

Guideline, Rev. 0, August 2002), internal dose is assigned to employees who were 

monitored but had no detectable activity (“positive”) in their samples and to 

employees who were not included in a bioassay program, because there is some 
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PER-049 Internal Dose Followup, page 4 September 9, 2022 

NOTICE: This document has been reviewed to identify and redact any information that is protected by the 

Privacy Act 5 U.S.C. § 552a and has been cleared for distribution.

amount of intake and associated dose that is not detectable by an internal 

dosimetry program. For employees who were monitored and who do have 

detectable activity (“positive”) in their samples, those sample results will be 

evaluated to ensure the method described in this TIB results in a greater 

probability of causation. To expedite the dose reconstructions, cases that met the 

criteria above will first be evaluated with the method described in this TIB. If the 

outcome yields a probability of causation >50%, a dose reconstruction using more 

reasonable assumptions will be performed. [NIOSH, 2004, pp. 3–4] 

OTIB-0002 assumptions

OTIB-0002, section 3.1, Assumptions,” states the following: 

For claims where it is considered likely that the covered employee had no 

significant internal radiation exposure, a method to expedite claims has been 

developed in accordance with 42 CFR 82.10(k)(2). This method assumes the 

“largest reasonably possible value” of the source term comprised of radionuclides 

that are/were typically the more significant radionuclides (by either 

preponderance or by internal dose significance) on a site. For this “worst-case” 

estimate of internal dose, it is assumed that on the first day of the first year of 

employment, the covered employee had an acute inhalation intake of each of the 

radionuclides in the source term, in the amounts listed below. [NIOSH, 2004, 

p. 4] 

Additional assumptions provided in section 3.1.1 include: 

• Inhalation intakes are the standard 5 micrometer activity median aerodynamic diameter 

(AMAD).

• The most soluble form of the radionuclides specified in International Commission on 

Radiological Protection Publication 66 was used. 

• Doses are calculated assuming 10 percent of the maximum permissible body burden 

• For sites without a reactor, table 3.1.1-2 lists 12 radionuclides of interest and associated 

parameters.

• For sites with a reactor, table 3.1.1-2 lists 28 radionuclides for which dose is calculated. 

• Table 3.1.1-4 lists 22 organs appropriate for applying the maximum internal dose. 

OTIB-0002 limitations

Section 5.0 of OTIB-0002 states the limitations of using this maximizing approach. Limitations 

applicable to this DR are as follows:

• The EE’s initial hire date was after 1969. If OTIB-0002 is used prior to 1969, the DR

report much include an explanation that demonstrates the doses resulting from 

table 3.1.1-2 intakes overestimate actual or potential doses received by the worker. 

• The target organ must be listed in table 3.1.1-4. 
SC&A, Inc.

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• The EE has no significant exposure to uranium. 

• Employment must be at a U.S. Department of Energy (DOE) site or national laboratory 

with an active radiation protection program.

Reworked Internal Dose Estimates 

The reworked DR used the EE bioassay data to calculate internal dose. A summary of the 

approach used by NIOSH follows. 

The EE submitted several urine samples that were analyzed for total 

uranium.

NIOSH calculated both fitted dose to account for the positive results 

and missed dose to account for the less-than-MDA results.

The uranium results were reported in units of milligrams uranium per liter excreted urine 

(mg U/L). These results were normalized to a daily excreted urine volume of 1.4. Uranium was 

assumed to be enriched to 2 percent, and the specific activity of 1.05 picocuries per microgram 

(pCi/μg), 2.22 disintegrations per minute (dpm) per pCi, and the conversion factor of 

1,000 μg/mg were used in the conversion of units of mg/L to dpm/day.

Fitted uranium

The EE’s urine bioassay data were fitted in the Interactive Modules for Bioassay Analysis 

(IMBA) program, using a combination of chronic intakes and acute intakes to determine a fit that 

represented a reasonable overestimate of the actual intakes. Positive bioassay data were assumed 

to have a normal distribution with ±30 percent error, and the uranium-in-urine activity curve 

either overpredicted the urine bioassay data or was contained within the 30 percent uncertainty 

band. The acute intake dates were initially estimated to be the midpoint between the date of the 

positive sample and the previous negative sample. However, the intake dates were adjusted as 

necessary to arrive at a reasonable fit of the intake regimes to the bioassay data. IMBA was used 

to generated uranium intake activities associated with absorption types F, M, and S. A 

comparison of the absorption types showed that type S solubility resulted in the highest dose. 

Missed uranium

Missed dose was derived using one-half the appropriate MDA as bioassay input to IMBA. MDA 

values were taken from the EE’s bioassay records and the PGDP occupational internal dose 

TBD, ORAUT-TKBS-0019-5, revision 03 (NOISH, 2012). A chronic intake period of 

 was used. IMBA-generated uranium intake activities 

associated with absorption types F, M, and S were calculated and compared. NIOSH determined 

that type S solubility resulted in the highest dose.

Recycled uranium 

The recycled uranium components were also assessed. This assessment was based on the 

 operations ratios to uranium in ORAUT-TKBS-0019-5. Absorption types for the 
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recycled uranium components were determined using table 3-1 of ORAUT-OTIB-0060, 

revision 01, “Internal Dose Reconstruction” (NIOSH, 2014). 

Total uranium dose

The fitted doses were compared to the missed doses on a year-by-year basis and the higher 

annual organ dose used in the Interactive RadioEpidemiological Program (IREP). This resulted 

in the assignment of a total internal dose of rem. 
SC&A, Inc.

PER-049 Internal Dose Followup, page 7 September 9, 2022 

NOTICE: This document has been reviewed to identify and redact any information that is protected by the 

Privacy Act 5 U.S.C. § 552a and has been cleared for distribution.

References

National Institute for Occupational Safety and Health. (2004). Technical information bulletin – 

Maximum internal dose estimates for certain DOE Complex claims (ORAUT-OTIB-0002, 

rev. 01 PC-2). https://www.cdc.gov/niosh/ocas/pdfs/arch/tibs/or-t2-r1-p2.pdf 

National Institute for Occupational Safety and Health. (2012). Paducah Gaseous Diffusion Plant 

– Occupational internal dose (ORAUT-TKBS-0019-5, rev. 03). SRDB Ref. ID 117897 

National Institute for Occupational Safety and Health. (2014). Internal dose reconstruction

(ORAUT-OTIB-0060, rev. 01), SRDB Ref. ID 135808