Re(2): 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 got interested in the subject you raised. I apologize that I did not pay
attention that it was originally the question of radiotherapy and not of
radiopharmaceuticals which make a big difference of course. Nevertheless I
asked a friend and she confirmed that in radiopharmaceuticals used for
diagnosis the presence of certain radionuclides is not tolerated. For
instance in the use of Tl-201, which is used for myocard investigations the
nuclide Tl-202 is not welcome. The same is true for I-125 which is used in
invitro investigations. The impurity of I-124 must not exceed 1/1000 of I-125.

The radionuclide Ga-57 is produced by accelerators. The long lived and
unwanted impurities have to be kept to a minimum by optimizing the
accelerator production as to the irradiation time and the energy of the
beam. But Ga-57 is used very seldom now.

The question of Tc-99 and Tc-99m is difficult. Of course Mo-99 should not be
eluted from the generator. Tc-99m is of course not used for therapeutic
reasons (see above). Having made a quick calculation I think that the
concentration of Tc-99 might not be worth considering, even if it had been
eluted after a long weekend. But - whenever Tc-99 is present it will be
eluted together with Tc-99m.

Franz
Schoenhofer
Habichergasse 31/7
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