Health Risks of Ionizing Radiation: - Clark University

Figure 3-2. In the 1950s the panoramic X-ray machine was
invented to take a picture of the whole mouth with just
one exposure (www.nist.gov/public_affairs/licweb/dental.
htm).
There is a vast and growing literature on
this topic and we have not included all of the
available information; the studies reviewed here
are representative. Included in this section are
studies focusing on diagnostic exposure, treatment
for non-cancerous diseases, treatment for cancer,
irradiation of adults and of children, in-utero
exposure, and radiologists’ occupational exposure.
As a practical matter an individuals’ decision to
accept medical radiation exposure will always be
a matter of balancing risks; hopefully this section
can help inform that decision. Tables 3-1 through
3-4 summarize the studies discussed below. Table
3-1 includes diagnostic exposures to x-rays, tables
3-2 and 3-3 include other exposures for diagnosis
or treatment of benign disease, and Table 3-4 covers
cancer survivors who received radiation therapy.
3.2 Diagnostic exposures
Diagnostic radiation, commonly used in modern
medicine to detect the presence of health problems
such as a bone break or a tumor, is the largest manmade
source of radiation exposure to the general
public. The doses that patients have received from
this type of exposure have varied greatly over the
Medical Exposures 21
years and for the most part have been strategically
reduced over time. Doses currently vary by procedure
and by organ. A dental x-ray, for example, might
result in a thyroid dose of 0.1 mGy while a CT chest
scan 3 could result in doses of over 20 mGy to the
breast, lung and esophagus. Figure 3-1 shows one set
of “average” dose estimates for various procedures.
A good source of organ-specific dose estimates is
Berrington de Gonzalez and Darby 2004. Because
these exposures are so common and are so carefully
controlled (especially in recent years), they are a
good source of data for epidemiologic research.
Diagnostic x-rays. There is some evidence
linking diagnostic x-rays with leukemia. Gibson et
al. (1972) conducted a case-control study of leukemia
in adults who had been exposed to diagnostic xrays
in upstate New York, in Baltimore, and in
Minneapolis-St.Paul. This study found significant
risks of acute myeloid leukemia (AML) and chronic
myeloid leukemia (CML) in males. The RRs for the
lowest category of exposure, 11 or more x-rays, were
1.61 (p