Medical exposure of 1-year old (Sue Dupre, Princeton University)

["Leif E. Peterson, PH.D." <PETERSON@plato.jsc.nasa.gov>]

Dear Sue Dupre (and Radsafers):

Your inquiry as to which (what?) path to go down with regard to radiation
bioeffects in a 1-year who has undergone a head CT a many chest x-rays is
a somewhat complex issue.  But up front, you need to be sensitive about the 
feelings of the mother, and let her know that you are concerned and want to 
help her.  She asked Princeton for help, because she needs it.  

Generally, I always recommended that people ask the radiologist, who ordered 
the procedures, about doses and risks.  Afterall, a physician in a medical 
facility that can order x-rays can order someone in the medical physics 
department to estimate doses and look at risks.  If a medical physicist is 
not on staff, then there would most likely be a consultant physicist for the 
institution who performs all of the equipment performance evalautions from 
which you can obtain dose (and possibly risk) information.  The bottom line 
is that the mother first needs to contact the radiologist(s) who performed 
the evaluations, and ask them about the doses and associated risks.  Then 
see what materializes.  From my experience, radiologists seem to be good 
about this, but there may be some who are reluctant to help out as you
indicated in your earlier message about mammography doses and likely risks.

I did some calculations about two years ago, for a 1-year old girl who died
of acute leukemia in the United Kingdom.  We based our risk data on the 
Life Span Study of Hiroshima atomic bomb survivors, and had to make some 
_large_ leaps fo faith about risk projection.  We knew that our estimates 
of risk suffered from *assumption bias*, since 1) the risks we generated 
were for a population rather than an individual, 2) there are problems
with *generalizing* risk from the Japanese population, 3) use of a 
dose-rate-reduction-effectiveness factor of 2 is conservative.  But I think
we may have used a DRREF of unity.  Despite all of the bias we suffered
from, I think the data were in fact used during litigation.  I never heard
the results of the decision -- ignorance is bliss!  

So there are some things that one can do to estimate risks, whether or not 
these risks are a step in the right direction, is subject to
debate.  There is a voluminous literature on childhood cancers following
medical irradiation, and the three scientists who come to mind are Drs.
George Kneale, Alice Stewart and Margaret Tucker.  You might do a search
on their names to look at some of their latest work.  Although most of my
time is spent with vital statistics (cancer rates, atomic bomb survivor
risk coefficients, life tables, etc.) for adults, I don't at all feel 
comfortable going outside the narrow bandwith of my area of knowledge 
because I don't follow the literature in this area.  If your inquiry was 
for an exposure during pregnancy, called *in-utero* exposure, I would probably
have been in a better position to help you with effects such as untoward
pregnancy outcomes, small head size, reductions in sitting height, reduced
mean school scores (koga, in Japanese) and IQ among children exposed
in utero during the Hiroshima and Nagasaki atomic bombings.  But these 
estimates would also be subject to the sources of bias outlined above.

My recommendation is to ask the mother to talk to the child's radiologist.
It is always best to let the physicians (who prescribed the exposures) inform
the parent about risks, since they are obligated to do so.  Since I am not
a physician I, I like to stiff-arm these issues and "dance around" them
when possible.  From a medico-legal framework, I place physicians at a higher 
level than scientists, and therefore feel compelled to put the onus on them.    
If you get in a snag, call the American College of Radiology.  A name
that rings a bell is Otha Linton.  I suspect that you receive quite
a bit of suggestions from the Radsafers on this one.  

With best regards,

-L.P.

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Leif E. Peterson, Ph.D., M.P.H.      Internet: peterson@plato.jsc.nas.gov
Epidemiologist/Health Physicist          SPAN: (Solar Physics Alert Network)
Kesley-Seybold Clinic, P.A.                    peterson@9.24.span.nasa.gov
NASA/JSC Mail Code SD23                Voice:  713.483.6470
Houston, Texas 77058 USA                 FAX:  713.483.3395
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