Clarification of Answer by
welte-ga
on
01 Jul 2006 12:43 PDT
Hi again,
The 14.57 mSv is somewhat higher than the typical range for neck CTs,
and may indicate that multiple scans needed to be taken (and are
counted as one). Another possibility is that the current was
increased to get a better quality scan, etc.
Your total exposure was about 20mSv, causing an increased lifetime
risk of cancer of 0.1% (total risk 20.1%). This estimate on increased
risk refers to cancers that typically appear on the order of 20-30
years after exposure, meaning that people who have this level of
radiation exposure, but who are already 90 years old, are unlikely to
live long enough to realize an actual fatal cancer from the radiation.
Their risk is the same, provided they live long enough. In your
case, the 0.1% increased risk is more meaningful, since you are quite
likely to live another 20-30 years.
In any case, as I stated, the Health Physics Societies states that
adverse effects have not been reliably documented below exposures of
about 100 mSv, so the 0.1% increased risk is likely more theoretical
than real. In other words, below about 100mSv, the increased risks of
getting cancer are so small that they are dwarfed by other risk
factors, making it almost impossible to do studies that are large
enough to establish that a cancer was likely caused by prior radiation
exposure.
In terms of reproductive risks, the Health Physics Society has an
excellent summary of both the risks with regard to gametes (sperm,
eggs) and to a fetus:
http://hps.org/hpspublications/articles/pregnancyandradiationexposureinfosheet.html
"According to published information, the reported dose of radiation to
result in an increase incidence of birth defects or miscarriage is
above 20 rad or 200 mSv."
They also state that during the first 2 weeks of pregnancy, doses of
much greater than 50mSv are required to induce a miscarriage.
In terms of damage to sperm or testes, the same source states
"For those patients who remain fertile after [radiation] therapy,
their reproductive risks are not increased significantly. In other
words, the risk of birth defects in the next generation for those men
who remain fertile and conceive is quite low. Studies of the atomic
bomb survivors indicate even in the high-exposure group that there is
not an increased incidence of chromosome abnormalities or genetic
disease in the next generation. That is also the case for studies from
the National Cancer Institute, which indicate that patients who had
cancer and received chemotherapy and radiation did not have an
increased incidence in genetic disease or birth defects in the next
generation although they did have problems with infertility."
Regarding exposure to ovaries, a question relating to a higher dose,
in this case to the abdomen and pelvis rather than the neck (closer to
the ovaries, so higher dose) was answered by Dr. Brent of HPS,
indicating that the risk of mutations passed to a child approach zero:
http://hps.org/publicinformation/ate/q2988.html
Finally, the iodine used for CT contrast studies is not radioactive.
It is more radio-opaque than blood, and so shows up within the
vessels. This helps to distinguish, for example, lymph nodes from
blood vessels, etc., which is particularly important in the neck,
where the anatomy is quite complicated.
I hope this information is helpful.
-welte-ga
,
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