Re: Radiation Risks

[David Scherer <scherer@uiuc.edu>]

I have to disagree with Al T.  I don't think that radiation risk is being
singled out over al others.  Just this morning I heard that the CPSC is
advising everyone with children under 6 to take down any imported vinyl
mini-blinds.  Apparently, Pb is used in the formulation and when exposed to
sunlight, some Pb can be released from the product.  (Even the small amount
of Pb previously used in solder for Cu water pipes is banned.)  I also heard
the FAA blasted for being lax on small, growing airlines.  The sound-bite I
heard claimed the public was exposed to unacceptable risks because the FAA
didn't want to give the industry a black eye.  Excuse me, but I thought that
air travel was among the safest modes of travel in the world.  The Delaney
clause prohibits _any_ additives in food (no matter how small the
concentration) if they _might_ be carcinogenic.  The claim that radiation is
singled out appears to border on the paranoid.  The public is adverse to
_any_ risk that is perceived to be high-tech or man-made.  (Excuse me,
human-made.)

On the matter of informing patients of radiation doses for medical
exposures, again, the discussion seems a bit simplistic.  Perhaps you missed
one of Mike Bohan's many good points: what dose do you want?  Entrance skin
dose?  Organ doses?  Effective dose?  To standard man or to the particular
patient (the geometries and attenuation properties are sometime very
different).  In the case of peds, does anyone have Monte Carlo calculations
for all the different sizes/ages that are encountered?  Presenting
quantative information is far more difficult than it may seem.  Even knowing
technical factors (kVp, mAs, distance), anatomical site, and exposure is
insufficient to reporduce the dose.  The beam quality and attenuation
properties vary markedly based depending on the filtration.  In addition,
scatter is highly dependent on the patient.  Often, scatter contributes mor
than half of the dose; in some cases much more.  So a single, meaningful
number is not readily available.

What's more, if we did give a numerical idex of risk, we would again be
treating radiation differently from other risks.  Patients are usually given
qualitative assessments of risk.  E.g., "A small percentage of people have
reactions to iodinated contrast media.  These reactions can be severe and
they, rarely, result in death."  For major procedures, there have been
clinical studies that reveal themortality rates.  In those cases, physicians
may include that information in the informed consent.  But the level of
detail in commensurate with the risk, especially the acute risk.

I do agree, however, that hospitals should be able to give numerical
information to those who ask.  (This question comes up frequently,
especially in children's hospitals.)  If there were more in-house diagnostic
medical physicists, the ballpark numbers would be readily available.  But
the current business climate in the medical industry makes that seem
unlikely.  In any event, it is more important to get this information
_before_ the exam as part of the informed consent to do the study.  Getting
the dose afterwords is like closing the barn door after the (insert favorite
domesticated animal) has left.

At least that's my opinion.

Dave Scherer
scherer@uiuc.edu