Health Risks of Ionizing Radiation: - Clark University

20 Medical Exposures
Figure 3-1. Average doses from diagnostic radiation exposures (values from http://www.ans.org/pi/resources/
dosechart/).
large doses to many small doses. Because most of
the doses have been administered in a controlled
way we have very good dose information for these
patients and they can provide good insight into
the patterns of radiation risk. Studies of the health
effects of medical radiation also provide important
insights into risks of a variety of exposure patterns,
into risks of cancers with long latency, and into the
relevance of in utero risk estimates to adult cancers.
These studies can also organize unique sets of data
about the effect of fractionated doses due to the
scheduled dose patterns that many patients receive.
Despite having good exposure information,
medical radiation studies, like other radiation
studies, are uncertain. Study results and estimates
of risk vary 2 . Uncertainty in this area comes from a
number of factors:
• Dose distributions are often anatomically
heterogeneous; administration of iodine-131 for
hyperthyroidism will result in a huge dose to the
thyroid but a negligible dose to the brain or the
bones.
• Patients undergoing radiotherapy, particularly
cancer therapy, may have a predisposition to
the same effects that the therapy can be causing;
distinguishing the underlying risk from the
radiation-induced risk can be difficult.
• Exposure is often received in adulthood and
many radiotherapy-induced cancers, with long
latent periods, may go unnoticed.
• The healthy worker effect is an issue in studies
of radiologists and technicians. It has often been
observed that health care professionals have
lower mortality and morbidity rates than the
general population and this can complicate the
interpretation of results.
• Retrospective studies often lack individual dose
information and therefore researchers are unable
to make dose-response relationship estimates
or comparisons with other studies of radiation
exposure (Berrington 2001). Although it is
possible to estimate doses based on the number
of years a worker was certified or the number of
x-rays a person thinks she had over the years,
this can lead to misclassification errors (Doody
1998).
2 This variability is exemplified in the difference between Gofman’s (1996) estimate that medical x-rays are responsible
for 62-90% of breast cancer and Evan’s (1986) estimate of fewer than 1%.