LNT -- Letter to NRC from ACNW

[Jim Hardeman <Jim_Hardeman@mail.dnr.state.ga.us>]

Fellow RADSAFE'rs --

Remembering the thread in this list a while back regarding
LNT, I thought that you might be interested in the following.

Enjoy!

Jim Hardeman, Manager
Environmental Radiation Program
Environmental Protection Division
Georgia Department of Natural Resources
4244 International Parkway, Suite 114
Atlanta, GA 30354
(404) 362-2675   fax: (404) 362-2653
Jim_Hardeman@mail.dnr.state.ga.us

------------------- 96-100.txt follows --------------------

           United States Nuclear Regulatory Commission
                     Office of Public Affairs
                       Washington, DC 20555
              Phone 301-415-8200   Fax 301-415-2234
                       Internet:opa@nrc.gov
No. 96-100                              FOR IMMEDIATE RELEASE
                                      (Thursday, July 11, 1996)

NOTE TO EDITORS:

     The Nuclear Regulatory Commission has received the
attached report from its Advisory Committee on Nuclear
Waste.  The report, in the form of a letter, provides
comments on the health effects of low levels of ionizing
radiation.

                                #


Attachment:
As stated

#                                        July 10, 1996





The Honorable Shirley Ann Jackson, Chairman
U.S. Nuclear Regulatory Commission
Washington DC  20555-0001

Dear Chairman Jackson:

SUBJECT:   HEALTH EFFECTS OF LOW LEVELS OF
IONIZING RADIATION

The health effects of ionizing radiation are central to many of
the regulations that are promulgated by the Nuclear
Regulatory Commission (NRC).  The validity of the linear- no
threshold (LNT) dose-response relationships in the area of
low doses and low dose rates has been questioned.  This
letter supports the Commission's present course of action of
a review and analysis by the National Council on Radiation
Protection and Measurements (NCRP) leading to an
evaluation of this important issue.  

Our discussion and recommendations concerning this
subject derive from the first meeting of the Joint
Subcommittee of the Advisory Committee on Reactor
Safeguards (ACRS) and the Advisory Committee on Nuclear
Waste (ACNW) held on March 26, 1996.  Presentations were
made by members of the NRC staff, including the visiting
medical fellow, and representatives from institutions and
agen- cies such as the NCRP, the Health Physics Society,
and the Massa- chusetts Emergency Management Agency. 
Written comments were also received from the public.

Most national and international scientific committees dealing
with the subject take the view that the safest approach to
regulation is one that relies on the LNT model of response to
doses of ionizing radiation.  This model holds that the ill
health effects observed at high doses and high dose rates
(mainly among atomic bomb survivors) can be extrapolated
linearly to low doses and low dose rates, down to the
smallest doses.  The NRC staff prepares regulations on the
basis of this model.  One of the basic questions in this field
is whether the LNT model is valid at the low doses and rates
normally encountered in many of the regulatory domains. 
The increasing emphasis placed by the Commission on
risk-informed regulation makes it imperative that the actual
health risk of low levels of ionizing radiation be assessed
accurately. 

The NRC is currently funding a contract with the NCRP to
make a critical evaluation of the LNT assumption.  The
ACNW has not reached conclusions on the validity of the
LNT model, and will continue to study the matter.  We see
the NCRP study as an opportunity to obtain an independent
review of the data and their quality.  

The presence of unavoidable background radiation and the
need for very large samples have made it difficult in the past
to obtain definitive data on the validity of the LNT model.  As
with all small-effects phenomena, the quality of the data and
the statis- tical interpretation of the results govern the ability
of any study to contribute to the testing of the model. 
However, investigators in the field have recently been able to
account for the effect of such confounding factors such as
variation in back- ground radiation.  Some studies in the
United States, as well as in China, Sweden, Poland, and
Canada, have arrived at conclusions that do not support the
LNT model.  Other research concludes that it is likely that at
least a threshold or perhaps a corresponding zero equivalent
point with beneficial risk decrements (hormesis) exists at
lower doses.  

A notable example of the latter is a ten-year study by Johns
Hopkins University of U.S. nuclear shipyard workers which,
we were told, showed lower mortality, no increase in
malignancies among workers exposed to radiation when
compared to those who were not exposed, and no "healthy
worker effect."  This study may be particularly significant
since the investigators were looking for evidence to support
the LNT model.  Another study, of Canadi- an women
patients in tuberculosis sanitariums who underwent re-
peated fluoroscopy to monitor response to therapy, is used
fre- quently to show the validity of the LNT model, but
examination of data at lower doses shows significant
beneficial effects.  The 1994 report of the United Nations
Scientific Committee on the Effects of Atomic Radiation
(UNSCEAR) contains an extensive appendix detailing cellular
repair mechanisms (called "adaptive response mechanisms")
that could contribute to an explanation of a threshold, or, if
such cellular responses were stimulated by low doses of
radiation, to an explanation of beneficial effects.   In contrast,
some of the public comments received by the Subcom-
mittee suggested that the LNT model underestimates the
harmful effects of low doses of radiation.  Also NCRP Report
No. 121, "Principles and Application of Collective Dose in
Radiation Protection," issued November 1995 and discussed
with the Joint Subcommittee at its March 26, 1996 meeting,
finds that "from the point of view of the scientific bases of
collective doses for radiation protection purposes, it is
prudent to assume the effect per unit dose in the low-dose
region following single acute exposures or low-dose fractions
is a linear response."    

In the face of conflicting views, the general belief of the
national and international committees dealing with the matter
has been that using the LNT model for regulatory purposes is
a safe and conservative approach and, if there is error, it is
on the side of enhanced protection.  However, if there is a
health benefit at low doses, this logic is incorrect.  Even if
there is no evident health benefit, there are significant
societal costs associated with this conservatism that could
be avoided or reduced if a threshold level could be
established below which no harm occurs.  A basic principle
of risk-informed regulation is to prevent a situation in which
scarce resources are misspent to avoid negligible risks,
while significant risks remain unattended for want of
resources to deal with them.  Owing to the potentially
significant costs of the present conservatism, we conclude
that a reexamination of the regulatory model is appropriate.  

It is obvious that agreement on an appropriate dose-response
model is made more difficult by the differing voices on this
subject within the scientific community and those outside of
this community, including regulators, policy makers, and
members of the public.  The first task required to reach such
an agreement is an impartial review of the data and their
quality in the face of the extensive application of the LNT
model in regulations and scientific opinion.  

We recommend that the need for special attention be
conveyed to the NCRP regarding its study.  Such attention
should include:  (1) assurance that the study includes
scientists other than those who are "recognized experts"
with a reputation built on the LNT model, (2) an evaluation of
the data by an entity with expertise in statistics or
information science, but no prior position on
LNT - such as the National Institute of Standards and
Technology (NIST) as well as the NCRP study committee,
and (3) consideration of essentially all studies that could
relate to the LNT.

The Committee strongly believes in the NCRP goal of
critically evaluating data related to low dose health effects. 
We will follow the program through interaction with NRC's
Office of Research and will report to the Commission on the
study and its implications. 

                               Sincerely,

                                 /S/

                               Paul W. Pomeroy
                               Chairman, ACNW