>> In this module,
we'll summarize the information presented in this training
and discuss some take home messages.
Over separate modules in this training,
we touched on radiation epidemiology
and its contributions to our understanding of health effects,
on the strengths and limitations of selected radiation studies,
and on how you should be cautious
in interpreting results from such studies.
We live in a world where radiation exposures to all
of us are increasing; in medicine, in the environment,
in certain occupations, in travel, and in the development
of nuclear technologies.
There is concern
about radiological accidents and intentional acts.
In whatever area or circumstance you can think of, we have more
and more exposures to radiation.
So radiation epidemiology is needed.
It was needed in the past and it is the foundation
for creating radiation protection standards
and guidance needed by regulators,
decision makers and managers.
Radiation epidemiology also is needed now and certainly
in the future as the issues facing the nation are becoming
more complex.
There is a focus on conducting studies
of large populations exposed to low doses at low rates,
the type of exposure we are concerned
about in our daily lives and occupations.
There are continuing needs to inform regulators,
decision makers and managers on the latest understandings
of radiation risks associated with changing circumstances.
This need was emphasized
in recent Government Accountability Office
or GAO reports on radiation research.
Is there enough human capital to meet those needs?
Are there enough radiation professionals?
This is an area of concern for the National Council
on Radiation Protection and Measurements as well
as many radiation agencies and industries.
Another take home message is
that all studies have limitations,
and some are more limited than others even if published
in high-visibility journals.
Some studies are useful and reliable, and others are not
and should be discounted in decision-making.
Hopefully, I've provided some basic understanding of what
to look for to separate the wheat from the chaff,
the good from the flawed, the reliable from the unreliable.
So what is helpful
to distinguish the reliable from the unreliable?
The study must have sound epidemiologic methods;
procedures to design, conduct and analyze the study properly.
You should consider: whether the population is well-defined;
whether the information on radiation dose and outcome,
such as cancer occurrence, is comparable between exposed
and unexposed; whether one group received special screening
that the otherw didn't; whether the follow-up
and outcome ascertainment was complete and comparable
between the exposed and non-exposed;
whether the study size was adequate
to detect an effect had there been one; whether the likelihood
of serious biases, such as selection bias
or information bias was high;
whether serious confounding influences,
such as cigarette smoking, were accounted for or addressed;
whether the dosimetry, that is the estimates
of radiation doses were of highest quality.
Was there any dosimetry?
Were doses estimated for individuals?
Many studies can be discounted solely
because of unreliable dosimetry.
You've also got to have comprehensive
statistical analyses.
When you're dealing with low doses, the choice of parameters
that you put into your statistical models can make the
difference on whether your study is statistically significant.
Statistical significance is probably overplayed,
it does not mean that a result is causal or not;
it suggests that the play of chance might be reduced somewhat
as a possible explanation for the findings.
But statistically significant results can be totally biased
and wrong.
The analyses should be transparent
to understand what was done, and not just a phrase
"we used logistic regression."
Are the results consistent with other reliable studies
or are they inconsistent?
If the study is the only one in the world
that reports enormously high or enormously low risk,
this suggests the likely possibilities of serious errors.
Were the results biologically plausible?
For example, is it plausible that a CT exam
of the abdomen would cause a brain tumor?
Is it biologically plausible that radiation
in a single study would increase the risk
of all individual cancers and by the same amount?
Even for cancers not known to be increased following radiation?
Having a dose gradient helps in making causal interpretations.
Did the conclusion hang on subgroup analyses,
sort of like cherry picking
to emphasize the result the authors appeared to have wanted?
Is the paper balanced or just one-sided,
discounting limitations or contradictory information?
And be aware that in the radiation arena there is a group
who believe, that radiation at low doses is good for you.
They are proponents of radiation hormesis.
They claim that there is evidence for a threshold below
which there are no radiation effects,
or the effects are good ones.
They are against using the
"linear non-threshold" dose response model for the purposes
of radiation protection.
On the opposite end of the spectrum, there is another group
who believe that radiation exposure is bad,
even a single radioactive molecule or a single gamma ray.
This group believes that all sources
of radiation exposure should be eliminated.
A related problem is the abuse of the concept
of collective dose as used in radiation protection.
Collective dose is when the estimates of individual doses
in a population are summed.
This might be done to consider whether cost-effective actions
could be taken to reduce this collective dose.
Misuse occurs when the collective dose is used
to predict numbers of cancer deaths attributable
to miniscule population exposures.
Radiation protection organizations, regulators,
and managers need to have the latest
and best epidemiologic findings
to make informed judgments and decisions.
Much of the study evaluations are just common sense.
If results seem peculiar or wrong, they probably are,
and careful scrutiny is called for.
There's not a simple checklist that separates the reliable
from the unreliable studies, but there are multiple
and diverse topics to focus on before coming
to your own conclusion
on whether a study is trustworthy or not.
Be skeptical, there's a lot of unreliable and flawed studies
out there and you should be aware of that.
This review that I've provided is not totally original,
except for my interpretation,
but based on the world's literature.
We have radiation reports
that review epidemiologic studies published periodically
from the United Nations, the National Academy of Sciences,
and from international and national protection
and scientific committees.
It's rather remarkable, I think, that we have standing committees
in the United States and throughout the world
that periodically review the effects of ionizing radiation.
The National Academy has a series of reports dedicated
to the biological effects of ionizing radiation.
At the National Council on Radiation Protection,
there is a continual review of the literature
on radiation epidemiology and biology.
A 2018 NCRP Commentary reviews the quality
of all recent epidemiologic studies considering methods,
dosimetry and statistics.
The World Health Organization has several volumes reviewing
the radiation literature.
No other carcinogen, not even tobacco, has such an array
of ongoing committees continually assessing
health effects.
Radiation is unique and because of population exposures
and population concerns, deserves, in my view,
this continued attention.
Thank you very much for this opportunity
to talk about my profession!