Re: Dose Calibrator Setting for I-123

[mikeg@SLAC.Stanford.EDU (Michael P. Grissom)]

I notice Peter didn't get much response from radsafe on this, so
here's an issue:  I'm curious about the higher level of "impurities", 
particularly radionuclidic impurities, for (p, 5n) I-123 vice 
(p, 2n) I-123.  In a series of nuclear imaging calibrations for
a LFOV gamma camera (and also used for a SPECT system review), I observed
significantly more interference from non I-123 radionuclides in the
gamma camera analyzers from (p, 2n) than from (p, 5n) I-123.  One
has to be careful in interpreting this since from a dosimetric
standpoint some weak gamma emitters (and any beta emitters) may be
making a significant contribution to the dose that might be delivered
to the patient.  However, we got our (p, 2n) I-123 from an Eastern
commercial radiopharmacy (relatively low energy cyclotron) and our 
(p, 5n) I-123 from P. Richards at Brookhaven National Laboratory's 
BLIP line (very high energy proton linac).  Mr. Richards (he has been 
retired for some time now) was famous for delivering very high purity 
I-123 as a "radiochemical" to our collaborative group and it should be 
noted that the radiochemistry and target purity/proton energy 
relationships obviously have big impacts on the final delivered product.  
On gamma spectroscopy in the analytical lab (back in the bad old Ge(Li) 
days!), we had significantly lower impurity levels seen with the (p, 5n) 
I-123 which was entirely consistent with the results of the imaging 
studies using a BRH line phantom to generate series of line spread functions.  
Hence, I presume there is a non-gamma (or very low energy gamma) emitter 
(one or more) that is causing the dose problems suggested by Syncor.
Anyone familiar with what they are?

This incidentally gets us back to where and how radionuclides are produced
for the medical and research communities in the U.S.  The national isotope
production facility needs to happen (in some way) to ensure the availability
of high quality radionuclides if many of the studies being done (some
literally life-saving) are to continue or improve in technological value.
--------------------
>We recently got a new CRC-15 ... When I talked to them they said the 
>I-123 from the p-2n reaction was the reason.  That the old 277 setting
>accounted for the higher level of impurities in the I-123 from the
>p-5n reaction.  The Syncor supplied I-123 is produced by Golden
>Pharmaceuticals [formerly North American Chemical formerly Benedict
>Nuclear Pharmaceuticals] and assay using the 277 gain setting gave a 
>reading consistent with Syncor's assay as did assaying it on the new CRC15.
>This implies that Capintec has not changed their recommended gain
>setting from 277.  Syncor/Golden's I-123 is also p-2n from Nordian
>International [same supplier as Mallinkrodt's]
> 
>Anybody out their know anything about what gain setting should be used?
>I'm going to call Syncor and Golden but wanted to post this quick befor
>the gateway clogs.  Thanks in advance to anybody who can shed some
>light on this.
>Peter G. Vernig RSO, VA Med Center, Denver, vernig.peter@forum.va.gov
>(303)399-8020 ex 2447
Michael P. Grissom
mikeg@slac.stanford.edu
Phone:  (415) 926-2346
Fax:    (415) 926-3030