Re: Beta Emitters and Dose Calibrators

[carol marcus <csmarcus@ucla.edu>]

At 11:04 AM 10/8/99 -0500, you wrote:
>Carol Marcus wrote:
>
>"Dear Radsafers:
>
>Yes, the error in the measurement can be significant, but that is a physics
>issue.  From the point of view of the accuracy that is needed in medicine,
>the error is of no significance.  So, why should we worry about it?"
>
>Carol- Your assertion that the error is of no significance may be true, but
>there is a need for more facts before you can convince me of it.  How much
>variability is there in dose calibrator response from one calibration geometry
>to another?  Do the people doing the assay realize the greater sensitivity
>to container material/geometry that beta emitters have compared to gamma 
>emitters?  Given that beta emitters are going to be used for therapy rather
>than just diagnostic imaging, I would think that delivering an accurate dose
>would be significantly more critical than for a diagnostic application.  What
>is a safe +/- range for therapy doses of Sr-89, P-32, Y-90 etc before you 
>start to cause serious injury to critical organs?  Is this range
>smaller or larger than the +/- range of the assay?
>
>
>John Laferriere, CHP
>DuPont Pharmaceuticals Co.
>Medical Imaging Division
>john.r.laferriere@dupontpharma.com
>Standard disclaimers.
>
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Dear John:

The work was done many years ago at Brookhaven by David Weber, Ph.D., now at
U.C. Davis, for P-32, for the NRC.  All the measurements were made ad nauseum.  

As far as what is medically required, that is a job for physicians to
determine.  If physicians were to need greater accuracy and precision with
some future therapy radiopharmaceutical, they will ask physicists and
engineers to develop something appropriate.  At present, we have no
problems.  Your assumption that more precision is needed for therapy than
diagnosis is dead wrong.  Many diagnostic tests require more precision
because of the technique and data processing involved.  Any old amount of
I-131 can treat hyperthyroidism, and if it isn't enough the first time, you
give a second or third dose.  The same patient can go to 2 doctors, and one
could prescribe 2 mCi and the other 30 mCi
and each doctor would manage to cure the disease.  

Ciao, Carol

<csmarcus@ucla.edu>

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