Your link with current trends in radiation dosimetry
RADIATION PROTECTION FOR THE
A candid interview with Stewart C. Bushong, Sc.D., Professor of Radiologic Science, Baylor University, College of Medicine
Editor’s Note: Since the publication of this article, regulations have been enacted requiring that dose to the embryo/fetus of declared pregnant
workers not exceed 500 mrem over the entire pregnancy. See Title 10 Part 20 of the Code of Federal Regulations or Landauer’s Nexus on the
new 10CFR20 for details.
Nexus: It is reported to us from mately 2 Gy (200 rads) no one will Dr. Bushong: There are basically
time to time that a pregnant die; therefore, 2 Gy is said to be two. Radiation-induced malignant
radiation worker was furloughed the threshold dose for radiation- disease,
or dismissed from her job because induced acute lethality. leukemia and
the employer became concerned cancer, and
over possible radiation injury to genetic change.
responds in a nonthreshold fash-
the unborn child. Is this proper
ion. If a large population were to Nexus: What about congenital
receive a 2 Gy dose, a small per- abnormalities?
Dr. Bushong: Absolutely not. centage of that population, less
Dr. Bushong: That type of re-
There are a number of protective
sponse to radiation is a threshold
devices and administrative proce-
type effect and certainly does not
dures to ensure that no harm will
occur at doses in the range of the
come to the unborn.
Nexus: Is there a safe dose to
Nexus: Then, for example, what
which a pregnant worker can be
is the risk of a newborn develop-
ing a childhood malignancy follow-
Dr. Bushong: There is an easy than 5%, would develop leukemia ing exposure to the MPD?
response to that question, but the several years later. Following 1
Dr. Bushong: To the best of our
true situation is much more Gy, approximately half of that
knowledge, the absolute risk of
complicated. The easy response is percentage would develop leuke-
radiation-induced cancer and
that the maximum permissible mia. Following even lower doses, a
leukemia in adults is approxi-
dose (MPD)—5 mSv (500 mrads) proportionately lower percentage
mately 30 cases in a population of
during pregnancy—is safe. would be expected to develop
1 million, each of whom has re-
leukemia. At doses in the occupa-
Nexus: Is this radiation level, 5 ceived a dose of 1 cGy (1 rad);
tional exposure range, there is a
mSv for nine months, considered an therefore, following 5 mGy (500
statistically predictable level of
absolutely safe level of radiation? mrad) to 1 million persons, one
would expect 15 cases or 1.5 cases
Dr. Bushong: Simplistically, yes. However, it is so small that it is
per 100,000. That estimate is for
But since we know that some not measurable.
adults receiving an abrupt expo-
possible radiation effects on the
Nexus: So even radiation doses sure, not one that is extended over
fetus are nonthreshold, there is
less than the MPD have a prob- time such as that which we re-
theoretically a vanishingly small
ability of producing an effect? ceive occupationally. It is, there-
probability of response following
fore, a worst case estimate. To
even lower radiation levels. Dr. Bushong: Yes, but the prob-
worsen the estimate further, let’s
ability is so very, very small that
Nexus: What do you mean by a assume that the entire MPD was
even if all pregnant workers
nonthreshold type of effect? received during the first trimester
received the MPD, no injury to
of pregnancy when the risk is
Dr. Bushong: Let’s first consider any unborn child would be ex-
approximately ten times higher.
a threshold type effect. Death, pected.
Therefore, one might expect as
following a single high exposure to
Nexus: Can you be more specific? many as 15 cases in 100,000. The
radiation, is a threshold type
First, tell us what radiation re- total number of active radiologic
effect. At doses less than approxi-
sponses are we talking about? technologists is approximately
Dr. Bushong: The principal absolutely necessary, especially if
Page 2 protective device is one that is temporary help would have to be
Concluded routinely used anyway, the lead employed to accommodate such a
apron. A radiologic technologist move.
receives nearly all occupational
100,000, certainly less than 1% of Nexus: Anything else?
exposure during fluoroscopy and
whom would be pregnant at any
portable radiography where Dr. Bushong: Yes. You can
time, so that the excess risk of
protective aprons are used. These provide the pregnant employee
such a harmful effect is only about
aprons do just what they are with an additional radiation
1/10th of a case.
designed to do—reduce the radia- monitor and instruct her to wear
Nexus: You mentioned genetic tion dose to near zero. it at waist level under the protec-
effects. tive apron. This monitor should be
Nexus: Can you be more specific?
identified as “baby badge” or “fetal
Dr. Bushong: The probability of a
Dr. Bushong: Very few radio- badge.” This is not specifically a
harmful genetic effect is only
logic technologists will exceed an dose reduction measure, but
about 1/10th that for malignant
occupational exposure of 1 cSv (1 rather to define more clearly the
disease and, therefore, it is of even
rem) in a nine-month period as fetal dose that is actually received.
recorded by a radiation monitor
Nexus: So do we understand that
Nexus: So if you consider the positioned at collar level above
there are no circumstances under
MPD to be a safe dose, what dose
which a pregnant employee should
is considered to be dangerous?
be terminated because of concern
Dr. Bushong: Let’s use the over her radiation exposure?
example of a patient who has been
Dr. Bushong: None. Furthermore,
exposed to diagnostic x-rays
there is no situation in which the
during pregnancy. If the exposure
pregnant employee should feel
occurred during the first trimes-
that she is placed at undue risk.
ter, we would not recommend an
the protective apron. Most will get That situation simply doesn’t
alteration in the pregnancy at
less than half of that, but for exist. With proper attention to
doses less than about 10 cGy (10
simplicity let’s assume 1 cSv (1 routine radiation protection
rads). Late in pregnancy, the safe
rem). The dose to the abdomen practices, the pregnant worker
dose rises to approximately 25
under the protective apron will be should not feel any more concern
cGy (25 rads).
approximately 5% of the collar for her unborn than she does
Nexus: Okay, you indicate that dose, or 500 µSv (50 mrem). Be- following the normal experiences
the MPD is a safe dose so there- cause of overlying maternal tis- and exposures of everyday life.
fore protective measures are not sues, the dose to the fetus will be Stewart C. Bushong, Sc.D., received
necessary. Right? only about 1/4th of the abdominal his B.S. in physics from the
Dr. Bushong: Wrong. Because entrance dose, or approximately University of Maryland. He went on
some responses of the fetus to 125 µSv(12.5 mrem). This is a to spend four years as a nuclear
radiation are nonthreshold in vanishingly small exposure and reactor physicist for the U.S. Public
certainly absolutely nothing to be Health Service and at Westinghouse
nature, it is important that we
concerned about. Atomic Power Laboratory.
reduce the fetal dose as low as
possible. Nexus: Can anything else be done? In 1966, he earned his Sc.D. at the
University of Pittsburgh and joined
Nexus: How do we do this? Dr. Bushong: Yes. There are the staff at Baylor University, College
Through the use of the devices perhaps two other procedures of Medicine. Currently, he holds the
and administrative procedures that should be followed. If staffing position of Professor of Radiologic
you mentioned earlier? permits, one could shift the preg- Science in the school’s Department of
nant employee from her normal Radiology.
Dr. Bushong: Yes. And, perhaps
we could consider the largest position to a job with potentially Bushong has authored more than 100
lower exposure. For instance, the scientific papers and has written 10
population of potentially pregnant books. One of his books, “Radiologic
radiation workers, radiologic radiologic technologist could be
assigned to radiography only, and Science for Technologists,” is the
technologists, as an example. popular standard in x-ray technology
removed from the fluoroscopy
Nexus: What protective devices training.
schedule and portable work.
can be employed? However, such a move is not
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