DCAS-PER-049 Subtask 4 –

Internal Dose Issue

Ron Buchanan, PhD, CHP

Advisory Board on Radiation and Worker Health, 

Subcommittee for Procedure Reviews

November 16, 2023
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Introduction

 2005: NIOSH’s dose reconstruction (DR) assigned a total internal dose of 

18.330 rem using ORAUT-OTIB-0002 (ORAUT, 2004) hypothetical model to 

derive intakes for a Paducah Gaseous Diffusion Plant (PGDP) case.

 2016: Under DCAS-PER-049, NIOSH’s reworked DR assigned a total internal 

dose of 33.244 rem using bioassay data and overestimating methods to derive 

intakes.

– Issue: This raised the concern that the hypothetical model may not provide an 

adequate overestimate of the intakes and resulting doses. 

 2023: Issue was addressed by NIOSH reworking the case using bioassay data 

and more reasonable, but claimant-favorable, DR methods. 

– Results: NIOSH’s 2023 DR resulted in a lower total internal dose and probability of 

causation (POC) than the two previous DRs.
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SC&A’s review of DCAS-PER-049

 2012: NIOSH revised sections 3, 4, and 6 of the PGDP site 

profile.

 August 5, 2016: NIOSH issued DCAS-PER-049 (NIOSH, 

2016) to address changes in the PGDP site profile that could 

affect DR.

 March 2, 2018: SC&A submitted its review of one case under 

subtask 4 (SC&A, 2018).
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2018 correspondence re internal dose issue

 March 6, 2018: Designated Federal Official (DFO) sent an email to SC&A 

inquiring why the hypothetical intakes resulted in internal doses that were about 

half of the internal doses estimated using the energy employee’s bioassay 

records.

 March 6, 2018: SC&A responded that there appeared to be a contradiction 

between the DRs concerning the results from the two internal dose methods 

(hypothetical and bioassay) that could use NIOSH’s clarification.

 March 7, 2018: The DFO requested that NIOSH clarify the different internal 

doses. SC&A was not informed of the outcome or whether NIOSH provided a 

followup.

 October 31, 2018: SC&A presented its subtask 4 review of PER-049 to the 

SPR. There were no findings, and the SPR closed the review.
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2022–2023 discussions concerning internal 

dose issue

 August 18, 2022: SC&A gave a presentation on the status of 

PER-049 subtask 4 and mentioned the internal dose issue to 

the Board. The Board ask SC&A to evaluate the internal dose 

in more detail and report its findings to the SPR.

 September 9, 2022: SC&A provided a memorandum to the 

SPR on the status of the internal dose issue (SC&A, 2022). 

 February 16, 2023: SC&A presented the internal dose memo 

to the SPR. The SPR discussed the issue and requested that 

NIOSH provide SC&A with the details of the DRs.
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Previous NIOSH DRs

 2005: NIOSH performed the original overestimating DR using 

hypothetical intakes and assigned a total internal dose of 

18.330 rem with a POC of 39.40%.

 March 2016: NIOSH reworked DR

– NIOSH input bioassay data in the Integrated Modules for Bioassay 

Analysis program (IMBA): 

• Used seven acute and three chronic intakes, as an efficiency method

• Resulted in an overestimate of intakes and projected organ internal doses 

–This rework resulted in a relatively large total internal dose of 

33.244 rem with a POC of 45.43%.
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NIOSH’s 2023 DR

 February 17, 2023: NIOSH reworked the case using bioassay 

data in IMBA and reasonable estimating methods:

– Analyzed the bioassay data and assumed nine acute and one chronic 

intakes.

– Resulted in a more uniform fit of the potential intakes.

– Derived a smaller total internal dose and a smaller POC.

 February 21, 2023: NIOSH provided SC&A with the general 

results of the reworked DR. SC&A requested more detailed 

information and calculation files. 

 May 2023: NIOSH provided SC&A with the detailed data and 

associated files.
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SC&A’s analysis of NIOSH’s 2023 DR

 August 2023: SC&A performed an analysis of NIOSH’s 2023 

reworked DR as follows: 

– Reran the IMBA program.

– Derived the uranium intakes.

– Derived the associated radionuclide intakes using the PGDP site profile 

ratio values.

– Derived the resulting annual and total internal doses (14.544 rem).

– Ran the Interactive RadioEpidemiological Program (IREP).

– Derived a POC of 33.86%.

 Results: SC&A’s total internal dose and POC value matched 

those derived by NIOSH for the reworked case. 
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Summary

 SC&A found that the 2016 DR, which was performed using 

bioassay data, employed overestimating methods.

 This resulted in the internal dose and POC being greater than 

the original 2005 DR that used hypothetical intakes. 

 NIOSH’s 2023 DR, which used bioassay data and reasonable 

estimating methods, but still claimant-favorable, resulted in a 

smaller internal dose and POC than either of the former DRs. 

 SC&A did not have any findings or observations concerning 

NIOSH’s 2023 reworked DR, assigned dose, or final POC.
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Conclusions

 It appears that the original case was not a good candidate and did 

not meet all requirements for using the ORAUT-OTIB-0002 

hypothetical internal intakes. 

 The 2016 rework of this case used overestimating methods in 

assessing the bioassay data.

 SC&A concluded that it is unlikely the hypothetical intake model 

would result in an underestimate of dose, if more reasonable 

estimating methods were used to fit the bioassay data. 

 SC&A has concluded that it is improbable this issue would impact 

other cases and recommends closing the issue.
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Questions?
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References

National Institute for Occupational Safety and Health. (2016). Paducah Gaseous Diffusion 

Plant (DCAS-PER-049, rev. 0). https://www.cdc.gov/niosh/ocas/pdfs/pers/dc-per49-r0.pdf

Oak Ridge Associated Universities Team. (2004). Technical information bulletin – Maximum 

internal dose estimates for certain DOE Complex claims (ORAUT-OTIB-0002, rev. 01 PC2). https://www.cdc.gov/niosh/ocas/pdfs/arch/tibs/or-t2-r1-p2.pdf

SC&A, Inc. (2018). DCAS-PER-049, subtask 4: Review of an Advisory Board selected case 

reworked for the evaluation of Paducah Gaseous Diffusion Plant technical basis document 

revisions (SCA-TR-2018-PER049-ST4, rev. 0).

SC&A, Inc. (2022, September 9). DCAS-PER-049 subtask 4 – Internal dose followup 

[Memorandum]. https://www.cdc.gov/niosh/ocas/pdfs/abrwh/scarpts/sca-per49-090922-

508.pdf