Research Subject Doses

["Gibbs, S Julian" <s.julian.gibbs@vanderbilt.edu>]

Our Clinical Radiation Committee and Institutional Review 
Board prefer to avoid stating radiation risk to research 
subjects as a probability of adverse effect, such as death. 
So doing would require adoption of some model; one can 
produce coherent arguments pro and con for basically any 
model of low-dose radiation risk.  We, instead, provide a 
statement of the time required for an average subject to 
receive an equivalent dose from natural background 
radiation.  Using the NCRP figure of 3 mSv/y, your 
procedure that delivers 500 mrem, or 5 mSv, would equate to 
about 1 y 8 mo of background.  This assumes that your 5 mSv 
was calculated as effective dose (or effective dose 
equivalent).  Obviously this does not completely avoid the 
issue of which model to use, since weight factors for 
effective dose are derived from linear dose-response 
models.  We think that our method is much less 
objectionable.
Use of time for equivalent background exposure provides 
information to the subject that is at least as useful as 
probability of adverse effect, at least for subject 
consideration for informed consent.  So far we have not 
encountered any objections to this method of risk 
expression.
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S. Julian Gibbs, DDS, PhD               Voice: 615-322-3190
Professor of Radiology                    FAX: 615-322-3764 
Dept. of Radiology & Radiological Sciences
Vanderbilt University Medical Center
Nashville TN 37232-2670 Email:s.julian.gibbs@Vanderbilt.Edu