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Probability of Causation (PC) News & Updates


Dependence of Cancer Risk on Dose and Dose Rate of Low-LET Radiation

This report describes a study for the National Institute for Occupational Safety and Health (NIOSH) to re-evaluate dose and dose-rate effectiveness factors (DDREFs) for low-LET radiation (photons and electrons) that are incorporated in cancer risk models in the Interactive RadioEpidemiological Program (IREP). The objective of this study was to develop recommendations that provide unbiased representations of the current state of knowledge of DDREFs for low-LET radiation.


Revision of Guidelines on Non-Radiogenic Cancers

On March 21, 2011, the Department of Health and Human Services (HHS) proposed to treat chronic lymphocytic leukemia (CLL) as a radiogenic cancer under the Energy Employees Occupational Illness Compensation Program Act of 2000 (EEOICPA or the Act) (76 FR 15268).

CLL is now treated as being potentially caused by radiation and as potentially compensable under the Act. This reverses the earlier decision by HHS to exclude this cancer from consideration. The final rule was published on February 6, 2012. This change became effective on March 7, 2012.

Please Note: The Final Rule does not add CLL to the list of “specified cancers” or qualifying cancers for the Special Exposure Cohort.

Public comment on this rulemaking closed on June 20, 2011. A complete electronic docket containing reviews of CLL radiogenicity and the CLL Risk Model and public comments can be found on the NIOSH Docket page, under Docket Number 209: PC – Nonradiogenic Cancer Reconsideration.


Changes to the NIOSH-IREP Lung Cancer Risk Model


Radiogenicity of Specific Cancers


Changes to the Dose Reconstruction Target Organ Selection for Lymphoma


New Procedure for Resolving Cases Close to 50% PC

There is a new procedure for resolving cases in which the upper 99th percentile credibility limit of probablity of causation (PC) is equal to or greater than 45% but less than 52% using the default simulation sample size of 2000 and default random number seed of “99.” This procedure became effective on June 6, 2006.

Previously, each case with an initial PC value falling between 45% and 50% at the upper 99th percentile credibility limit (C.L.) was processed by increasing the simulation sample size to 10,000, choosing a new random number seed, and rerunning the case in NIOSH-IREP. The resulting upper 99% C.L. of PC obtained with a sample size of 10,000 determined the case outcome, supplanting the initial PC value that had been obtained with a sample size of 2000. This procedure was adopted in order to provide better statistical precision for cases approaching the compensation threshold of 50%.

To achieve even greater statistical precision for cases close to the compensation threshold, the following new procedure was adopted on June 6, 2006 and replaces the procedure described above.

For cases in which the initial PC is equal to or greater than 45% but less than 52% using the default sample size of 2000:

  1. The simulation sample size will be increased to 10,000.
  2. 30 additional IREP runs will be performed, using a new random number seed for each run.
  3. The average value (arithmetic mean) of the upper 99% C.L. of PC of the 30 runs will determine the case outcome.
  4. For cases with more than one primary cancer in which the initial PC calculated from the “multiple primary” equation is equal to or greater than 45% but less than 52%, 30 runs will be performed for each primary cancer per steps 1 and 2 above. The arithmetic mean of the upper 99% C.L. of PC of the 30 runs for each cancer will then be entered into the multiple primary equation. The newly calculated PC, based upon the arithmetic mean PC value of each cancer as entered into the multiple primary equation, will determine the case outcome.

The NIOSH-IREP User’s Guide was revised to reflect this procedural change.

The following Program Evaluation Report details the effect of this new procedure on previous non-compensable cases.


Revision 1985 NIH Radioepidemiological Tables

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