>> Thanks very much.
It's a great pleasure to be here and I'm excited to speak
with you about epidemiology and ionizing radiation.
I'd like to discuss three issues
in interpreting published studies
that health professionals, managers
and decision makers should consider.
First, some studies are high quality and reliable,
and we will describe characteristics
of a high quality study.
Second, some studies are not
of high quality and are not reliable.
They shouldn't be incorporated into decision making.
Third, some studies are conducted with poor methods,
such as with poor or no measures of radiation dose
and inadequate statistical analyses- they are so flawed
that they cannot be interpreted.
Studies of human populations exposed
to radiation have become very sophisticated,
but many are very difficult to interpret, misleading,
or over interpreted, despite being published
in high-impact journals.
For simplicity, we will refer to these three categories
as reliable, unreliable and flawed.
In 2018, the National Council on Radiation Protection
and Measurements or the NCRP published Commentary 27,
supported in part by the CDC,
which critically evaluated 29 recent epidemiologic studies
as to their strengths, limitations and usefulness
for radiation protection decision makers.
In this module, we will discuss- what is radiation epidemiology
and what have we learned from 100 years
of radiation epidemiology research.
It would be good to start with some background information.
Let's begin with a definition of epidemiology.
It is simply the study of the distribution and causes
of disease in human populations.
It comes from the word "epidemics," epi means upon
and demos means people.
So it's the study of what causes disease in people.
And radiation epidemiology is simply the study of radiation
as the cause of disease in people.
I believe that many people are familiar with epidemiology
but in the context of infectious disease epidemiology,
which deals with flu, Ebola, and Zika viruses, or in the context
of epidemiologic departments that deal with food poisoning,
and other sources of population disease.
Radiation epidemiologists deal primarily with chronic diseases,
and cancer in particular, these diseases that occur many years
after radiation exposure.
Because of the wealth of knowledge on the health effects
of radiation on people,
radiation epidemiology has a huge impact
on setting radiation protection standards
for workers and public safety.
But the plethora of studies with conflicting
if not questionable results create confusion
for decision markers, standard setters, and the public.
How do you separate the wheat from the chaff?
What makes a study reliable
versus unreliable, or simply flawed?
Some of the limitations in the unreliable
and flawed studies render them uninterpretable
and they should not be considered for public policy
or risk assessment and management.
Epidemiologists, of which I am one,
have been studying populations exposed
to radiation for over 100 years.
We know about the effects of radiation at high doses,
especially when such doses are delivered at a high rate.
High doses, for example, occur during radiation treatments
for cancer, and high dose rates usually refer to exposures
that occur in less than a second or perhaps as much as an hour.
We have learned how to quantify or estimate the chance
that radiation causes specific cancers following specific doses
from the many studies conducted since the turn
of the last century, the early 1900s.
These studies begin with the early radiologists
who developed skin carcinomas and leukemia,
the radium dial painters who developed bone cancer,
the Japanese atomic bomb survivors in 1945, the children
who were treated for benign conditions,
such as enlarged tonsils, who later developed thyroid cancer;
the underground miners who breathed radon
and its decay products
and developed lung cancer many years later, the nuclear energy
and nuclear weapons workers who are still being studied,
the children living near Chernobyl after the accident
who drank milk contaminated with radioactive iodine
and developed thyroid cancer at a high rate,
the cancer survivors who developed second cancers later
in life, and even the astronauts who developed cataracts
or lens opacities from space flight and space radiation.
Recently, new information is coming from worker studies
where the exposure was gradual and over a period of years,
and not brief and at a high rate as in many other studies.
Radiation human studies have been ongoing for decades
and much knowledge has been gained about acute
and long-term health effects of workers and populations
that were exposed
to considerable amounts of radiation.
The radiation human studies continue to this day
and are used as the basis for radiation protection standards
and for compensation schemes related to claims
of ill health among atomic veterans who participated
in atmospheric nuclear weapons tests, and Department
of Energy weapons employees at Manhattan project facilities
such as Oak Ridge, Hanford, and Los Alamos.
Despite the decades of research in radiation epidemiology
and the vast amount of knowledge currently available,
there remain many important and unanswered questions.
Today, the focus of radiation epidemiologists has turned
to not whether radiation causes cancer,
but "how much cancer is caused by radiation"
and "does it matter at all whether you're exposed
to radiation briefly or chronically?"
As will be the theme of these discussions,
there are many epidemiologic studies out there
with conflicting results that create confusion
for decision makers, the public and even scientists.
So sound judgment from radiation professionals, managers,
and decision makers is needed to protect people
without unduly restricting the beneficial effects of radiation,
such as in medicine and in industry,
such as non-destructive testing with radioactive sources.
What have we learned from the past century of research?
Importantly, the focus on genetic effects - that is,
any effects of parental exposures that might result
in adverse effects in their children
and subsequent generations - has shifted to somatic effects
in individuals, for example, cancer.
There have been large-scale epidemiologic studies
of the children of parents who had been exposed
to the atomic bombings, and of children of cancer survivors
who were treated with radiation therapy.
No evidence for untoward effects on the children
of these exposed parents were found.
No increase following preconception exposure
to the gonads was seen for a variety of adverse effects
such as malformations, stillbirths, neonatal deaths,
cancer, multifactorial diseases such as diabetes,
or biological measures of possible changes
in genes transmitted from the parents to the children.
Has radiation damage to parents' gonads,
testes or ovaries been passed on to their children?
There hasn't been any evidence in humans,
although there is evidence in studies of mice.
Now we have switched concern to the individual to what about me?
Understandably, we were very concerned about our kids,
but it's now about the individual.
Here's what else we've learned.
You can get exposed once in your life and your risk of cancer
or your chance of developing a cancer remains
for your entire life.
And a one-time exposure
of sufficient dose is all that's needed.
The young are more susceptible
to developing cancer following exposure than the old,
but there are a few notable exceptions.
Another somewhat surprising finding from the study
of atomic bomb survivors is that exposure during pregnancy
to the fetus or embryo does not carry a greater risk
of developing cancer than exposure to a young child
under the age of 6 years.
In fact, prenatal exposures may carry a lower cancer risk
than exposures after birth to the young child.
Women are more susceptible than men, mainly because the breast
and the ovaries are highly susceptible
to radiation-induced cancer, whereas the testes
and prostate are highly insensitive.
One cancer site of current interest is the lung
where women, based on the atomic bomb survivor study,
appear to have a much higher risk
than men following radiation.
This is important to NASA in their guidelines
for space exploration,
and it limits the time women can spend in space.
But the evidence is conflicting and based on only one study,
albeit of very high quality.
Risk of developing cancer later in life, again the probability
that cancer might occur, differs by organ or tissue.
The bone marrow is very sensitive
and leukemia might develop.
The rectum and other tissues are very insensitive
and cancer risk rarely, if ever, is elevated following exposure.
Perhaps surprisingly, some sites have not been convincingly
or consistently linked to radiation exposure:
cancer of the cervix, the prostate, the pancreas,
chronic lymphocytic leukemia, malignant melanoma,
and Hodgkin lymphoma, for example, despite 100 years
of epidemiologic studies.
An interesting biological question is why this may be so.