Fluoroscopy and IRBs

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

J. Villanueva-Meyer expressed concern about regulation of x-ray fluoroscopy
doses to subjects who also receive radiopharmaceuticals during medical
research.  Here's my experience with fluoro and isotopes combined.

When you deal with the cardiologists who perform fluoro, you must first
recognize where each of them "sits" on the learning curve.  If the 
person who is going to the fluoro during the research project is at the
beginning of the curve, then you don't have a lot of flexibility in limiting
the amount of fluoro-time since the individual will be learning while he/she
is doing the procedure(s).  On the other hand, if you work with an estab-
lished fellow or attending cardiologist who has done a lot of fluoro, then
you can simply tell them to "keep the fluoro-time down" and they will
most likely say to you "no problem."  

So through control, i.e., "don't give my test subjects high doses," 
you can substantially reduce exposure.  In a recent experiment in
which astroanauts received tracers and fluoro to localize a catheter
placeed in the heart pre-flight, I sat down with the flight surgeon
before the procedures and decided that we would limit the cardiologist
to 1 minute of TOTAL fluoro-time.  It worked.  In fact,  a total of
1
 minute of fluoro wasn' t even needed.  This resulted in an 80% drop
in fluoro skin entrance exposures when compared with a previous 
experiment when ALARA was not used "as strongly."  In addition, most
IRBs I have been on let the RSCs decide if doses are an issue or
not.  We just finished a project that involved your IRB and Radiation
Safety Office (UTMB).  They seem to have a good handle on x-rays and
isotopes used with human research.  It was good to see that they wanted
effective doses and risks for all procedures (x-rays and isotopes)
before study approval was given.  

If you are still at a loss after reading this, do the following:

1).  Find out the skin entrance exposure rate (R/min) for the EXACT
       procedure to be performed with fluoro.
2).  Pick a starting number of 0.05 Sv (5 rem) and limit the dose
       to subjects at this level.  
3).  Estimate the effective doses for the proposed isotopes.
4).  Add up all expected doses.  If the total exceeds 0.05 Sv ( 5 rem),
      then figure out how many minutes of fluro would be needed to 
      meet the 0.05 Sv (5 rem) limit.  

If the use of Radioactive Drug Research Committee Drugs, i.e, use of
Tc-99m sprinkled on corn flakes for a GI bleed imaging study, is
proposed, then there are specific limits that are legally required
under FDA regulation.


L.P.