## CDC and NCI Responses to Key NAS Recommendations

The National Academy of Sciences Committee to Review the CDC-NCI
Feasibility Study of the Health Consequences from Nuclear Weapon Test
was asked by CDC to address the following specific questions:

> 1\. Are the methods and sources of information used in the technical
> report to estimate radiation doses and health effects from fallout
> appropriate for this study?
>
> 2\. Are the methods and results clearly presented in the main text of
> the technical report?
>
> 3\. Are the findings presented in the report supported by the data and
> analyses provided?
>
> 4\. Do the Options for Future Work presented in Chapter 6 represent an
> appropriate range of options for public health activities that could
> be pursued as a result of this study?

The Committee made the following comments and recommendations to CDC and
NCI. The CDC/NCI responses to these recommendations are also provided.

##### Estimates of dose from Nevada Test Site and global fallout {#estimates-of-dose-from-nevada-test-site-and-global-fallout .unnumbered}

***Recommendation:*** The committee recommends that changes be made in
the draft report to clarify the assumptions, methods, and uncertainties
related to dose estimation. Tables should be used to lay out the sources
of uncertainty in the dosimetry and in the estimation of risk. The basis
of a "credibility interval" of a factor of 3 for dose estimates should
be described in the text in a manner analogous to description of the
credibility interval for the risk estimation (given some dose).

***CDC/NCI Response:***

The main assumptions and the methods related to dose estimation have
been clarified in the body of the report. In addition, the Appendices D,
E, F, and G where the methods are explained in detail are referred to as
many times as judged appropriate. However, it was considered that a
systematic assessment of the uncertainties associated with the dose
estimates was not within the scope of this feasibility report. It was
subjectively estimated that the 90% credibility interval for dose
extends from a factor of about 3 below the dose estimate to a factor of
about 3 above the estimate. It is emphasized that this quantitative
estimate of uncertainty was provided for illustration only. In fact, the
uncertainties in the dose estimates vary according to the type of dose
that is considered, the conditions of exposure, and the lifestyle and
dietary habits of the population groups or individuals that are
considered. A much more detailed dose estimation process would be needed
in order to derive the uncertainties with a reasonable degree of
reliability. It would be carried out if the decision is made to exercise
Option 5.

***Recommendation:*** CDC and NCI should consider performing a
reanalysis of the ^131^I exposures to the American public that would
incorporate new dosimetry-related information from Chernobyl and
elsewhere, the contribution of global fallout, a more comprehensive
uncertainty analysis, and correction of acknowledged errors in the
previous dosimetry. However, the committee does not recommend an
expanded study of exposure to radionuclides other than ^131^I inasmuch
as the human doses were much lower than those of ^131^I, they confer
essentially non-detectable increases in individual risk, and the risks
are of little public-health significance.

***CDC/NCI Response:*** CDC and NCI acknowledge that the feasibility
report incorporates data available through Fall 2001, and that should
future research efforts be undertaken by either agency these should
include the topics addressed in this recommendation. It should be noted
that these analyses, particularly the estimation of the contribution of
global fallout to the ^131^I exposures of the American public and the
preparation of a more comprehensive uncertainty analysis, will require a
substantial effort and, although these updates might affect the
estimated doses, they would not change the report's conclusions
regarding the feasibility of a study.

**Document location and retrieval**

***Recommendation:*** The committee recommends an effort to retrieve and
archive additional relevant information about the nuclear-weapons
testing program. That means collecting data preserved in various
repositories that have not been cataloged and may be in danger of
imminent destruction. CDC should also:

-   Continue its search for documents not held by governmental agencies
    and take steps necessary to ensure their preservation.

-   Enroll other government agencies, especially the Department of
    Defense, in the effort to identify, preserve, and publish
    information.

-   Make copies of key documents, the data derived from them, and
    relevant computer codes or other calculation tools and make them all
    publicly available, including archiving and providing public access
    to all the databases and spreadsheets generated by the feasibility
    study and mentioned in it and its appendices, together with inputs
    and calculation tools used for other studies performed for NCI and
    CDC.

***CDC/NCI Response:*** CDC has a long history of conducting similar
projects, and will undertake this particular effort if resources are
identified. NCI will continue to process unique and unpublished fallout
data sets obtained by means of direct contact with fallout specialists.

***Recommendation:*** The committee also recommends that CDC urge
Congress to declare a government-wide moratorium on the destruction of
documents that are potentially pertinent to measuring fallout in the
United States and to mandate declassification of historical
fallout-related records.

***CDC/NCI Response:*** CDC will explore methods to communicate this
information to Congress and other stakeholders.

**Estimates of cancer and non-cancer risks**

***Recommendation:*** The committee recommends that more emphasis be
placed on levels of individual risk and the associated uncertainty and
less on population risk from collective dose. Although collective dose
and population risk may have some public health utility if the doses are
significant in the context of doses and risks from other sources, they
fail to show the size of the risk that individuals are likely to
experience, which is the key consideration for concerned citizens and
for most public-health implications. It is also important that the
executive summary and text compare putative lifetime risks posed by
fallout with risks posed by natural background irradiation and with
natural lifetime risks. Such comparisons will help to provide a
perspective for the general public to better understand the risks
related to fallout.

***CDC/NCI Response:***

Although qualitative statements are made in the report on the levels of
individual risk and of their associated uncertainties, it was considered
that quantitative estimates were beyond the scope of this feasibility
report.

With regard to the comparison of fallout and natural background
radiation, a section was added in Chapter 3 to describe the components
of natural background radiation exposure; this section includes a
presentation of the geographic variation of natural background exposures
in the continental U.S. in the form of maps, which allow a comparison
with the doses from fallout to be made. The corresponding risks are
considered in section 4.

***Recommendation:*** The potential that the dose-response association
might have a substantial upward quadratic component or a threshold
should be considered in modeling the risk of leukemia posed by fallout
radiation.

***CDC/NCI Response:***

The potential that the dose-response association might have a
substantial upward quadratic component or a threshold was mentioned in
the discussion of the risk estimates. The implications of dose-response
curves other than linear, however, were not assessed quantitatively in
the absence of refined dose estimates.

***Recommendation:*** There is no evidence that radiation doses of the
magnitude sustained from NTS or global fallout cause any of the major
non-cancer diseases (cardiovascular, respiratory, digestive or
genitourinary). A conclusion to this effect would therefore be
appropriate.

***CDC/NCI Response:***

It was clearly indicated in the report that, other than thyroid cancer
and leukemia, there is no epidemiological evidence that fallout caused
any other major disease.

**Communication with the public about exposure and cancer risk**

***Recommendation:*** CDC/NCI should develop a detailed public summary
and a communication plan for its distribution. The public summary should
provide information that can be readily understood by the lay public,
including comparison of background radiation with the radiation doses
discussed in the report of the feasibility study and a description of
the important uncertainties (related to dose and risk) that apply to the
feasibility study.

***CDC/NCI Response:*** CDC has developed a public summary, which will
be posted on its website
(http://www.cdc.gov/nceh/radiation/fallout/default.htm) and linked with
NCI's ^131^I/Nevada Test Site website materials. The public summary
discusses comparison with background radiation as well as the importance
of uncertainties in dose and risk estimates that apply to the
feasibility study.

***Recommendation:*** The agencies should phase information from the
feasibility study into the ^131^I/Nevada Test Site Communication Plan in
a timely fashion to give interested American citizens a more complete
picture of their exposure to NTS and global fallout with appropriate
explanations of relative health risks.

***CDC/NCI Response:*** A public summary providing information from the
feasibility study will be linked with the ^131^I/Nevada Test Site
Communication Plan on the NCI website. If additional information becomes
available through further research, CDC will ensure that it is also
added into these linked websites in a timely fashion.

***Recommendation:*** If Option 5 is adopted and important new
scientific work develops, CDC/NCI should produce a timely major
educational effort that builds on the efforts of the communication plan
for the ^131^I/Nevada Test Site study.

***CDC/NCI Response:*** If additional information were found that would
have significant impact on the data and/or conclusions in this
feasibility report, CDC and NCI could produce appropriate materials
building on the existing communication efforts related to the
^131^I/Nevada Test Site.

***Recommendation:*** CDC and NCI should make studies on radiation
exposure of US citizens transparent and accessible to interested
individuals. The committee recommends that interested citizens take part
in the study process and, with scientific and social science experts,
serve as members of advisory boards for such studies.

***CDC/NCI Response:*** Communication of study results to interested
individuals and the general public are important aspects of CDC and NCI
policy, and will continue to be emphasized in the areas of radiation
exposure and associated health effects, as well as others. We will also
continue to provide opportunities for interested members of the public
to participate in the study process and to serve on study advisory
boards.

***Recommendation:*** CDC and NCI should hold a follow-up conference,
similar to the one sponsored by NCI on risk communication (January
2000), as part of the continuing CDC effort to develop effective
guidelines for communicating radiation risk to the American public.

***CDC/NCI Response:*** CDC has held several meetings and roundtables in
which radiation risk communications has been a key topic. We will
continue to seek opportunities to add to the body of knowledge about
this important topic.