Re[2]: Dental X-rays

[julian.gibbs@mcmail.vanderbilt.edu]

     Thanks to all for your comments from my message yesterday.  I realized 
     that it was sketchy, but did not want to test system bandwidth or 
     reader's patience with the gory details.  A brief response, in no 
     particular order:
     
     We did dosimetry for panoramics, for 3 representative machines using 
     400-speed screen-film.  Results were effective dose equivalents of 
     0.01 to 0.02 mSv/film.  We used exposures determined empirically from 
     a sample of each make and model.
     
     The high-yield criteria were designed in an attempt to reduce 
     unnecessary x-ray exposure in dentistry by reducing the number of 
     unproductive exams.  It seems impossible to eliminate these entirely.  
     If every exam is positive, then the criteria were probably too rigid 
     and significant disease may have been missed.
     
     As in many fields, dissemination and implementation of new technology 
     in practice lags well behind research.  The long-term solution is 
     upgraded radiology curricula in dental schools.  Radiology is not 
     recognized by the American Dental Association as a specialty of 
     dentistry, so curriculum quality varies greatly among schools.  There 
     is a major current effort to obtain specialty recognition for dental 
     radiology.  It was very nearly accomplished last year, and probably 
     will be in the next few years.
     
     For our Monte Carlo calculations we used optimum skin exposures by 
     technique and beam energy, measured by Larry Crabtree at CDRH in the 
     mid-80s.  These were determined for optimum conditions of darkroom QA, 
     etc., and are less than those from DENT, NEXT, etc.  I don't think the 
     data were ever published.  We used organ weighting factors from ICRP 
     26.  The ICRP at that time was quite dogmatic that the term effective 
     dose equivalent could be used only with those factors.  Our anatomic 
     input was obtained from head-to-foot CT scans of a typical adult 
     female cadaver.  We had dose for the entire remainder.  Our results 
     are strictly applicable to adult female patients.  Other investigators 
     have since published results of measurements and calculations of 
     effective dose equivalent for dental exams.  Results agree reasonably 
     well, given the large uncertainties of the method.
     
     Sorry to ramble on so long--but you asked for it.
     

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     S. Julian Gibbs, DDS, PhD                           Voice 615-322-3190
     Professor of Radiology                                FAX 615-322-3764
     Vanderbilt University Medical Center
     Nashville TN 37232-2675    Internet julian.gibbs@mcmail.vanderbilt.edu
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