Re: Radionuclide impurities in Therapeutic Dosages

[schoenho@via.at]

At 17:59 30.10.1996 -0600, you wrote:
>     
>     A colleague has enquired as to what levels of radionuclide impurities 
>     would be acceptable in radiopharmaceuticals of therapeutic dosage 
>     magnitudes.  An alternate way of phrasing his question would be "what 
>     level of unwanted absorbed dose or equivalent dose is acceptable due 
>     to contaminating trace impurities in a radiopharmaceutical?"
>     
>     The application is that some radioisotopes for pharceuticals can be 
>     chemically extracted from high level radioactive waste and might 
>     contain impurities such as Cs-137, Pu isotopes, uranium isotopes, etc.
>     
>     Obviously the impurity should be a negligible contributor to the total 
>     dose from the agent - but does anyone care to offer an opinion on what 
>     that percentage or absolute magnitude might be?  I am unaware of any 
>     pertinent FDA guidance or any other guidance on this particular 
>     subject.
>     
>     Thanks in advance.
>     
>     Gene Carbaugh
>     Pacific Northwest National Laboratory
>     eh_carbaugh@pnl.gov
>
>===========================================================

Gene,

I am not an expert in radiopharmaceuticals, but the problem of "impurities"
is usually not the question of fission products, plutonium or uranium
isotopes. Many radionuclides for radiopharmaceuticals are produced by
accelerators by special nuclear reactions. The radionuclides produced are
usually short lived, so their dose to the person which they are adminstered
to is rather low. This is the reason why they are used! There is the
possibility of byproducts from unwanted reactions, which produce long lived
radionuclides or radionuclides with unwanted decay (beta or alpha radiation). 

One classic example of an unwanted radionuclide is Tc-99, which accumulates,
if Tc-99m generators are not used for a long time. When Tc-99m is milked
from the generator a relatively large amount of unwanted long lived Tc-99,
which is furthermore a beta-emitter, will be injected into the patient
together with Tc-99m.

Franz
Schoenhofer
Habichergasse 31/7
A-1160 WIEN
AUSTRIA/EUROPE
Tel./Fax:	+43-1-4955308
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e-mail:		schoenho@via.at