National Institutes of Health
                                    
                      WHAT WE KNOW ABOUT RADIATION



1.  What is radiation?
     We live in a sea of radiation.  There are many different
types of radiation, some of which are visible light, ultraviolet
rays from the sun, infrared from a heat lamp, microwaves, radio
waves and ionizing radiation.  Radiation is said to be ionizing
if it has sufficient energy to displace one or more of the
electrons that are part Of an atom.  This creates an electrically
charged atom known as an ion.  Common examples of ionizing
radiation are x rays and their cousins, gamma rays, which are
emitted by radioactive materials.  Others include beta rays,
which are also emitted from radioactive materials, and neutrons,
which are emitted during the splitting (fission) of atoms in a
nuclear reactor.

2.   When do we encounter ionizing radiation in our daily lives?
     Everyone who lives on this planet is constantly exposed to
naturally occurring ionizing radiation (background radiation).
This has been true since the dawn of time.
     Sources of background radiation include cosmic rays from the
sun and stars; naturally occurring radioactive materials in rocks
and soil; and radioactive isotopes (unstable radioactive
counterparts to naturally stable atoms) normally incorporated
into our body's tissues; and radon and its products, which we
inhale. Radon exists as a gas and is present in soil from which
it seeps into the air.  Radon gets trapped inside buildings,
especially if the ventilation is poor.  Levels of environmental
radiation depend upon geology, how we construct our dwellings,
and altitude.  For example, radiation levels from cosmic rays are
greater for people On airplanes and those living on the Colorado
plateau.  However, the risk of cancer has not been shown to vary
consistently with the levels of background radiation.
     We are also exposed to ionizing radiation from man-made
sources, mostly through medical procedures.  On the average,
doses from a diagnostic x ray are comparable to natural
background radiation.  Radiation therapy, however, can reach
levels many times higher than background radiation but this is
usually targeted only to the affected tissues.  We are also
exposed to ionizing radiation from color televisions, smoke
detectors, building materials, mining and agricultural products,
and coal-burning.  People who smoke receive additional radiation
from radioisotopes in tobacco smoke.

3. How do we know about the effects of high doses of ionizing
radiation?
     The adverse effects of high doses radiation were seen
shortly after the discovery of radioactivity and x rays in the
1890s.  In 1902, skin cancers were reported in scientists who
were studying radioactivity. Back then, no one took special
precautions in working with radioactive materials because their
effects were not yet fully recognized.  The occupational hazards
soon became apparent.  For example, a 1931 report described cases
of bone cancer in women who wet their brushes on their tongues to
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get a good "point" for painting radium on watch dials.
Radiation's role in causing leukemia in humans was first reported
in 1944 in physicians and radiologists.
     Much of our data On the effects of high doses of radiation
comes from survivors of the 1945 atomic bombs dropped on
Hiroshima and Nagasaki and from other people who received high
doses of radiation, usually for treatment.  The National Cancer
Institute (NCI), part of the National Institutes of Health (NIH),
in collaboration with the Radiation Effects Research Foundation,
an international group supported jointly by the U.S. Department
of Energy and the Japanese Ministry of Health and Welfare,
continues to study the long-term effects of radiation on the
survivors of the bombs.  Only about 12% of all the cancers that
have developed among these survivors are estimated to be related
to radiation; only about 9% of the fatal cancers in these people
are estimated to be related to radiation.  Uranium miners and
those who lived near the Nevada nuclear weapons test sites used
from 1951-1963 are also among those being monitored in order to
learn more about the effects of high doses of ionizing radiation. 
NCI is also helping to set up studies of the people most affected
by the Chernobyl nuclear power plant accident, especially the
children who lived nearby and the workers who cleaned up the
plant after the accident.  The information from all these studies
has been and will continue to be published--after rigorous
review--in medical and scientific journals that are available to
everyone.  

4.   What are some of the beneficial ways in which ionizing
radiation is used in medicine and in medical research?
          The discovery of x rays in 1895 was a major turning
point in diagnosing diseases because physicians finally had an
easy way to "see" inside the body without having to operate. 
Newer x-ray technologies such as CT (computerized tomography)
scans have revolutionized the diagnosis and treatment of diseases
affecting almost every part of the body.  Other sophisticated
techniques have provided physicians with low-risk ways to
diagnose heart disease.  For example, doctors can now pinpoint
cholesterol deposits that are narrowing or blocking coronary
arteries, information essential for bypassing or unclogging them.
     Every major hospital in the United States has a nuclear
medicine department, in which radioisotopes are used to diagnose
and treat a wide variety of diseases more effectively and safely
by "seeing" how the disease process alters the normal function of
an organ.  To obtain this information, a patient either swallows,
inhales, or receives an injection of a tiny amount of a
radioisotope.  Special cameras reveal where the isotope
accumulates briefly in the body, providing, for example, an image
of the heart that shows normal and malfunctioning tissue. 
Radioisotopes are also used in laboratory tests to measure
important substances in the body, such as thyroid hormone. 
Radioisotopes are used to effectively, treat thyroid diseases,
including Graves disease--one of the most common forms of
hyperthyroidism--and thyroid cancer.
     The use of ionizing radiation has led to major improvements
in the diagnosis and treatment of patients with cancer.  These
innovations have resulted in increased survival rates and

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improved quality of life.  Mammography can detect breast cancer
at an early stage when it may be curable.  Needle biopsies are
more safe, accurate, and informative.when guided by x-ray or
other imaging techniques.  Radiation is used in monitoring the
response of tumors to treatment and in distinguishing malignant
tumors from benign ones.  Bone and liver scans can detect cancers
that have spread.
     Half of all people with cancer are treated with radiation,
and the number of those who have been cured continues to rise.
There are now tens of thousands of individuals treated and cured
from various cancers as a result of radiotherapy.  In addition,
there are many patients who have had their disease temporarily
halted by radiotherapy.  Radioisotopes are also being used to
decrease or eliminate the pain associated with cancer- - such as
that of the prostate or breast-- which has spread to the bone.
     Radioisotopes are a technological backbone for much of the
biomedical research being done today.  They are used in
identifying and learning how genes work.  Much of the research on
AIDS is dependent upon the use of radioisotopes.  Scientists are
also "arming" monoclonal antibodies--that are produced in the
laboratory and engineered to bind to a specific protein on a
patient's tumor cells--with radioisotopes.  When such "armed"
antibodies are injected into a patient, they-bind to the tumor
cells, which are then killed by the attached radioactivity, but
the nearby normal cells are spared.  So far, this approach has
produced encouraging success in treating patients with leukemia.
Most new drugs, before they are approved by the Food and Drug
Administration, have undergone animal studies that use
radioisotopes to learn how the body metabolizes them.
     Another clinical and research tool, PET scanning (positron
emission' tomography), involves injecting a small amount of a
radioisotope into a person to "see" the metabolic activity and
circulation in a living brain.  PET studies have enabled
scientists to pinpoint the site of brain tumors or the source of
epileptic activity, and to better understand many neurologic
diseases.  Researchers were able to learn how dopamine--the
chemical messenger (neurotransmitter) that's involved in
Parkinson's disease--is used by the brain.
     These are but a few of the many vital uses of ionizing
radiation in medicine.  About 70 to 80 percent of all research at
the National Institutes of Health is performed using radiation
and radioactive materials.  NIH research has consistently
produced results that have improved the health of the American
people.

5.   What are the adverse effects of ionizing radiation?
     Ionizing radiation can cause important changes in our cello
by breaking the electron bonds that hold molecules together. For
example, radiation can damage our genetic material (DNA) either
directly by displacing electrons from the DNA molecule, or
indirectly by displacing electrons from some other molecule in
the cell, which then interacts with the DNA.  A cell can be
destroyed quickly or its growth or function may be altered
through a change (or mutation) that may not be evident for many
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years.  However, the possibility of this inducing a clinically
significant illness or other problem is quite remote at low
radiation doses.
     Our cells, however, have several mechanisms to repair the
damage done to DNA by radiation.  The efficiency of these repair
mechanisms differs among cells and depends on several things,
including the type and dose of radiation.  There also are
biological factors that can greatly modify the cancer-causing
effects of high doses of radiation.
     The severity of radiation's effects depends on many other
factors such as the magnitude and duration of the dose; the area
of the body exposed to it; and a person's sex, age, and physical
condition.  A huge dose of radiation to the whole body at one
time can result in death.  Exposure to high levels of radiation
can increase the risk of developing cancer.  Because a radiation-
induced cancer is indistinguishable from cancer caused by other
factors, it is very difficult to pinpoint radiation as the cause
of cancer in a particular individual.
     Other effects of high doses of radiation include suppression
of the immune system and cataracts.  Certain tissues of a fetus,
particularly the brain, are especially sensitive to radiation at,
specific stages of development.  An increased rate of severe
mental retardation has been found in atomic bomb survivors whose
mothers were 8-25 weeks pregnant when the bombs were dropped.
However, the children and grandchildren of the atomic bomb
survivors so far have shown no greater incidence of genetic
problems than unexposed populations.
     It is very difficult to detect biologic effects in animals
or people who are exposed to low-level radiation.  Based on
studies in animals and in people exposed to high doses of
radiation such as the atomic bomb survivors, scientists have made
conservative estimates of what might be the highest doses that
would be reasonably safe for a person over a lifetime.' But these
calculations are estimates only, based on mathematical models.
Even so, the U.S. government uses these estimates to set the
limits on all potential exposures to radiation for-workers in
jobs that expose them to ionizing radiation.  International
experts and various scientific committees have, over the years,
examined the massive body of knowledge about radiation effects in
developing and refining radiation protection standards.

6.   Should patients be concerned about the radiation they may
receive from tests that their physicians have ordered?
     The doses involved in medical procedures have been
decreasing over the past two decades as x-ray films and equipment
have been improved.  In addition, the ability to target radiation
more precisely to one part of the body has resulted in less
exposure to the rest of the body.
     It is always wise to avoid unnecessary radiation exposure.
Physicians routinely compare the risks of radiation to the
benefits derived from a diagnostic use of radiation to ensure
that there is more benefit to the patient than risk.  In many
cases, such diagnostic tests enable doctors to treat the patient
without invasive and life-threatening procedures.
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     Radiologists, health physicists, the National Council on
Radiation Protection and Measurements--the Congressionally
chartered independent advisory group that, among other things,
recommends what the U.S. radiation standards should be--and other
responsible parties are continually seeking ways of minimizing
risk while retaining or improving the benefits from medical uses
of radiation.

7.   Should patients be concerned about the radiotherapy they
undergo for cancer treatment?
     Radiation, surgery, and chemotherapy are the mainstays of
cancer treatment and are used in combinations depending on the
cancer.  Certain tumors can be treated successfully with
radiotherapy alone.  The effectiveness of radiation in killing
cancer cells--and, at the same time, the potential for harm to
normal tissues--depends on several things. including the type of
radiation used, the extent of the body that is treated, and the
patient's age or other medical problems.  Doctors try to avoid
exposure of large parts of the body to radiation because this can
cause serious side effects like cancer.  However, only about 5%
of all secondary cancers--ones that develop after treatment for
the initial cancer- -have been linked to radiotherapy.  The risk
of leukemia after high doses of radiation to localized areas of
the body often is surprisingly low, because the local effect is
to kill cells that might, at lower doses, undergo transformation
-- the changes that a normal cell undergoes as it becomes
malignant --eventually leading to leukemia.  Other side effects
of radiotherapy range from mild to serious; many are temporary.
     With the development of better machines and the use of
computers to plan the treatment, the safety and efficacy of
radiotherapy has steadily improved.  Radiologists make every
attempt to minimize harmful effects to normal tissues.  Thus, a
patient's risks from exposure to radiation are far offset by the
benefits from the treatment.

8.   Should patients or normal volunteers be concerned about
participating in medical research studies in which they may be
exposed to some radiation?
     The U.S. government takes measures to protect the rights and
welfare of everyone who participates in medical research studies.
By law, studies involving humans and funded by the U.S.
government must first be approved by the Institutional Review
Board (IRB) of the hospital or university where the study will be
conducted.  The IRB, composed of a group of individuals with
backgrounds in science, ethics, and other fields, must ensure
that all risks to the participants are justified on the basis of
potential benefits either to themselves or to society and that
their rights will be protected.  This regulation applies to all
studies, including those in which the use of radiation is
proposed.  It is also the IRB's responsibility to ensure that
patients or volunteers are fully and accurately informed of the
risks and benefits of participation in the study, are not coerced
in any way into participating, and are competent to make the
decision to participate.  (If the studies will be conducted in
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children, then parental consent and assent by the child is
required.) When the use of ionizing radiation is involved, nearly
all such institutions also have a group of radiation health
experts (the radiation safety committee) review the proposed
research before it can be approved to proceed.

     9.   Should people be conceded about ionizing radiation?
     Most of the radiation that we are receiving is naturally
occurring background radiation.  Some level of exposure to
radiation is unavoidable.  It appears, however, that the cancer
risk from very low-dose exposure is quite low.  It is prudent to
avoid unnecessary exposure, but not if one loses more--in money,
time, convenience, or increased risks from other things--by
avoiding radiation rather than ignoring it.
     The cancer risk associated with exposure to high-levels of
ionizing radiation is among the best understood of any
relationships involving environmental agents that cause cancer;
this relationship continues to be studied and reevaluated.  This
knowledge is constantly used in evaluating the risks and benefits
of the uses of radiation in medicine.  In the overwhelming
majority of cases where it is used, the benefits of medical
radiation far outweigh the risks associated with it, but there is
a tradeoff.  In this sense, radiation is no different than any
other diagnostic or therapeutic agent, except that we have more
information than usual.
          Properly managed, radiation can be used for great
benefit to humanity and with minimal risk, a risk comparable to
or lower than those commonly accepted as an ordinary part of
daily life such as driving to work.

Prepared by the Office of Communications, OD, NIH April Il, 1994