Schmidt CW 2012. CT
Scans: Balancing Health Risks and Medical Benefits. Environ Health Perspect
120:a118-a121.
http://dx.doi.org/10.1289/ehp.120-a118
[excerpts] "CT
scanners emit X rays. Different tissue types absorb X rays in varying amounts,
and the resulting contrasts provide detailed images of anatomy and disease. Absorbed radiation can break chemical bonds in tissues,
liberating charged ions (hence the term “ionizing radiation”) that can damage
DNA and produce cancer should cells be unable to repair themselves. Nonionizing radiation—lower-energy radiofrequency waves
such as those emitted by microwave ovens and cell phones—doesn’t break chemical
bonds....
...The dominant risk
assessment model appears in a 2006 report from the National Research Council’s
Biological Effects of Ionizing Radiation (BEIR) subcommittee.6 The BEIR VII model postulates there is no safe level of ionizing
radiation exposure; carcinogenic effects are assumed to follow a linear dose
response, meaning even the smallest exposure carries some level of cancer risk. The BEIR VII model generates so-called lifetime
attributable risk (LAR) factors, which estimate the likelihood of cancer in
hypothetical individuals as a function of dose. Multiplying the LAR by the
number of people exposed to a given dose yields an estimate of expected cancers
from that exposure in the population....
The AAPM’s position
statement asserts that cancer risks are negligible at effective doses below 50
millisieverts (mSv) for single CT exposures and below 100 mSv for multiple
exposures over short durations. But a 2003 paper coauthored by David Brenner,
director of the Center for Radiological Research at Columbia University School
of Public Health, claims that the atom-bomb survivor data work well for
low-dose extrapolation because they’re drawn from large cohorts with
well-defined exposures and complete followup.9 And those data, Brenner says, show a statistically significant
trend of increasing cancer risk with increasing organ dose between 5 and 100
mSv. Smith-Bindman echoes his conclusions, arguing that cancer risks are
established even at effective doses of 10 mSv...
Brenner DJ, et al. Cancer
risks attributable to low doses of ionizing radiation: assessing what we really
know. Proc Natl Acad Sci USA 100(24):13761–13766. 2003. http://dx.doi.org/10.1073/pnas.2235592100
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