The International Role of RERF
Among investigations providing the
basis for radiation protection standards worldwide, the
atomic-bomb survivor study is the most long-standing and
extensive ever undertaken.
|by Warren K Sinclair, president emeritus,
US National Council on Radiation Protection and Measurements,
and RERF visiting director
|This article is abridged from a talk
given at ceremonies held in June 1995 in Hiroshima and Nagasaki
to mark RERF's 20th anniversary. Attending the event were
present and past employees as well as representatives of citizen's
groups, the local and national governments, RERF's funding
agencies, and the US National Academy of Sciences. This article
originally appeared in RERF
Update 8(1):6-8, 1996.
|We are here this afternoon to celebrate
the 20th year since the Radiation Effects Research Foundation
(RERF) was founded, thus beginning the unique Japanese-American
collaboration that succeeded 27 years of atomic-bomb survivor
studies conducted by the Atomic Bomb Casualty Commission (ABCC).
These studies have led to what we now recognize, worldwide,
as the most informative findings on the delayed effects of
ionizing radiation on man ever obtained.
'Discovery' of radiation
This year is 1995, which marks a century of man's awareness
of ionizing radiation as a factor in his life. Röntgen
discovered x rays in 1895 and put them to manifold use at
once, including in medicine. In 1896, Becquerel discovered
the radioactivity of uranium, which was followed by the discovery
of other radioactive substances, such as radium by Marie Curie.
Obviously, radioactivity and ionizing radiation have been
present naturally in the universe since the beginning of time,
but man finally became aware of them just 100 years ago. The
discovery of radioactivity opened the field of nuclear physics
and quickly led Rutherford and others to an understanding
of the structure and composition of the atom and, indeed,
of nuclei themselves.
Today, we recognize that radiation is an inevitable part of
our lives and that natural background radiation is ubiquitous
on Earth. It consists of radon exposure, external terrestrial
exposure, internal radionuclides, and cosmic radiation, which
result in a dose to the individual of about 3 mSv per year
(NCRP Report 93, Bethesda, Maryland, USA, 1987). Assuming
linearity at low doses, the risk of cancer associated with
natural background may be of the order of 1%, ie, about 1/20th
of the cancer risk due to all other causes. In the US, individuals
receive on average about another 0.6 mSv per year from manmade
sources, mainly medical.
Putting radiation to work
Man also has put ionizing radiation to a broad range of uses,
including industrial, agricultural, medical, and nuclear power,
thus providing the opportunity for further exposure to manmade
sources (International Atomic Energy Agency, Highlights
of Activities, IAEA, Vienna, 1993). With these uses--some
involving large amounts of radiation and radioactivity--comes
the inevitability of accidents. However, in spite of widespread
use, comparatively few fatal accidents have occurred in radiation
work. By 1995, a total of 389 accidents had taken place--some
3,000 persons exposed significantly and 112 fatalities (not
counting possible later cancer deaths) (Radiation Emergency
Assistance Center/Training Site Accident Registries, Oak Ridge
Institute for Science and Education, Oak Ridge, Tennessee,
These activities occupationally expose radiation workers (about
4 million worldwide) to an average of about 2 mSv per year,
which is about equal to a doubling of natural background radiation
except for radon. This effectively doubles the radiogenic
component of their risk.
The good news about radiation protection is that in the US,
while the number of workers has grown from about 500,000 persons
to 2,000,000 between 1960 and 1990, the average dose of those
exposed has decreased by more than a factor of 2 because of
the "as low as reasonably achievable" philosophy and other
radiation protection pressures. In the US nuclear industry,
the decrease has been more rapid and greater--more than a
factor of 3 (from over 6 mSv/y on average in 1980 to under
2 mSv/y on average in 1990).
Except for accidents involving high doses, radiation protection
today is not concerned with direct deterministic effects--erythema,
cataract, sterility--because the low doses involved in most
occupational settings are below the thresholds for these effects.
However, stochastic effects--cancer and genetic effects--may
be caused at low frequency after low-dose exposures. The major
radiation protection question is: "What is the frequency (or
risk) of cancer after a specific low dose of ionizing radiation?"
Source of most radiation risk information:
All of our information on these risks comes from exposed human
populations, of which by far the most important are the survivors
of the atomic bombings at Hiroshima and Nagasaki, although
some medically exposed populations and some occupationally
exposed populations provide important complementary information.
Cancer induction after ionizing radiation is, of course, a
delayed effect. Leukemia has a minimum latency of two years
and a peak incidence at about six to eight years. Solid tumors
have a minimum latency of about five to ten years, and thereafter
incidence rises as the natural cancer rate increases with
age at least up to 40 years after exposure.
Internationally, the responsibility of informing the world
community on risk estimates for induced cancer is undertaken
by the United Nations Scientific Committee on the Effects
of Atomic Radiation (UNSCEAR) and, in the US, by the Advisory
Committee on the Biological Effects of Ionizing Radiation
(BEIR) of the US National Academy of Sciences (NAS). These
bodies consider the relevant worldwide data from exposed populations
and estimate the risk. Internationally, the International
Commission on Radiological Protection (ICRP) and, in the US,
the National Council on Radiation Protection and Measurements
(NCRP)--informal professional bodies--use these risk estimates
as the basis for recommendations on limits of exposure for
workers and the public. Governments usually frame their radiation
safety legislation on the ICRP and NCRP recommendations.
I have been personally involved with UNSCEAR from the 1977
report onwards and with the ICRP since 1977 (especially during
the drafting of the ICRP 1990 recommendations), and I also
have been president of the NCRP through most of that period.
Consequently, I have considered these radiation risks from
both international and national viewpoints.
The largely US-funded ABCC and, more recently, the RERF have
assessed the epidemiological data on excess cancer deaths
in their program approximately every four years beginning
in 1961. These data have formed the basis of input to UNSCEAR
and BEIR periodically. It warrants noting that a risk estimate
is actually a risk coefficient, ie, the number of excess cancers
per unit population divided by the dose causing the excess.
Thus, the dose also is important and also has been evaluated
carefully at intervals for the RERF program, stimulated by
both NCRP and NAS committees. The latest revision, known as
Dosimetry System 1986, was approved for use at RERF by both
US and Japanese national dosimetry committees.
|The extent of the cancer risk information
available to UNSCEAR has increased over time (Table
1), derived mainly from the ABCC-RERF Life Span Study
(LSS) but supported by some other studies. Information has
increased through the years so that a single value for leukemia
risk in 1958 has evolved into individual risks for about ten
organs and a "remainder" in 1994. The estimated lifetime risk
(high dose rate) for all cancers was about 10%-12%/Sv in the
1988 and 1994 reports. I believe that will not differ greatly
when LSS Report 12, which incorporates data up through
1990, is completed and published in 1996 [Pierce et al, Radiation
Research 146:1-27, 1996]. BEIR committee evaluations follow
a pattern similar to those of UNSCEAR and generally have found
Why is the RERF Life Span Study
more important than any other radiation-related study?
A summary of the number of cancer deaths altogether as of
1985 indicates 339 excess cancer deaths among about 6,000
cancer deaths. This is not a large number statistically, especially
when it is broken down into individual cancer sites.
the LSS, because of the number of persons involved and the
range of doses received (up to high doses), has more power
than any other study to do the following:
We are now beginning to see in the early and imprecise results
of occupational studies (from the US, UK, and Russia) risk
data that are similar to those from the LSS as interpreted
by the ICRP (UNSCEAR, 1994). This is important confirmation.
- to produce risk estimates for total cancer, mortality,
- to produce risk estimates for 10-20 individual organs;
- to demonstrate the shape of the dose response;
- to find the lowest doses for which there are statistically
significant risks (LSS Report 11: 0.2 Sv; LSS
Report 12: 0.05 Sv);
- to examine the effect of variables such as age and sex;
- to follow the fate of the youngest cohorts: 0-9 years
old and 10-19 years old at the time of the bombings;
- to demonstrate latency and whether the risk of solid
tumors decreases with time; and
- to demonstrate cancer risks in sensitive groups such
It is not only for total risk estimation that the LSS is so
powerful. The 1994 UNSCEAR report also considered risks by
individual site from all sources as completely as possible.
For some sites, such as the breast, the number of sources
is extensive. The average risk derived from all studies is
about the same as the LSS value, the standard against which
all other studies are measured.
The RERF LSS not only has all this power with respect to cancer
induction but it also yields information on noncancer effects
as well, including acute effects, mental retardation among
those exposed in utero, delayed noncancer effects, and genetic
effects. Note that here I am focusing on the human effects
studies arising from the LSS program. I am not addressing
the entire RERF research program which includes the important
radiobiological and other studies that have always been a
part of the program.
Applications of the cancer mortality
The RERF LSS risk data are invariably the standard for risk
estimates and form the basis for the following:
Probably the most important single application is the underlying
basis of low-dose radiation protection standards. The change
in risk estimates based on RERF LSS data collected up through
1988 caused the ICRP (and NCRP) to lower limits for workers
in 1990 for the first time in over 30 years from an average
of 50 mSv/y to an average of 20 mSv/y. Limits for the public
were similarly lowered.
- standards for radiation workers;
- standards for the public;
- probability of causation assessment in a wide variety
- assessing the impact of accidents;
- assessing the risk to the public of environmental exposures;
- assessing the risk to soldiers and others exposed to tests, etc; and
- assessing effects on special groups, eg, fetuses (mental
For the data up through 1985, only 39% of the LSS population
had died and been evaluated. For LSS Report 12, which
covers the data up through 1990, the figure is about 44%.
The change in percentages expected in the future can be
calculated easily from the characteristics of the Japanese
population (in 1990).
The most important groups, about which we so far know little,
are the 0- to 9-year-old group and the 10- to 19-year-old
group. The population demographics with respect to these
groups are shown in Table 2. In 1990, only 6% and 14% of
these two groups had died and could be evaluated. By the
year 2010, 44% of the 10- to 19-year-old group are projected
to have been evaluated, as compared with only 20% of the
youngest (0- to 9-year-old) group. In my view, the epidemiological
and statistical study must continue at least until that
time and in modified form perhaps even longer.
| Table 2. Decrease in numbers of atomic-bomb
survivors in the youngest cohorts (percent alive)
| aAt the time of the bombings
Note: Calculations by Dale Preston, RERF Department
of Statistics, June 1995.
|Long-term projects require enormous
patience on the part of everyone concerned: the study subjects,
the scientists, the managers, and the funding sources, ie,
the Japanese Ministry of Health and Welfare and the US Department
of Energy. The latter especially has had severe funding pressures
mainly, but not solely, because of fluctuations in the yen-dollar
exchange rate. In spite of these difficulties, the RERF program
must continue strongly for the sake of future world knowledge.
It is fitting, in this 20th year, to quote James Liverman,
who, in 1975 as assistant administrator of DOE's predecessor
(the Energy Research and Development Agency), was instrumental
on the US side in bringing about this unique binational research
foundation. "I regard the binational RERF as a great move
forward in Japanese and American science. . . . I am very
proud of it," he said in June 1995.
In closing, let me say that the RERF staff has not only made
a great success of this ongoing binational project but it
has contributed enormously and uniquely to the worldwide knowledge
of radiation-induced cancer and to many other delayed effects
as well. Without you and the splendid cooperation of the atomic-bomb
survivors, the world scientific community would still be floundering
on this important subject. However, we still have much to
learn, especially about the youngest groups of survivors.
Thank you for what you have done so far. I wish you Godspeed
in what you will do for the world scientific community tomorrow.