Risø National Laboratory, Roskilde, Denmark; 2 The Niels Bohr by nig11470

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									The 108Cd(α,2n)110Sn nuclear reaction – A production route to the PET-
radionuclide 110mIn


H. Thisgaard1,2 , M. Jensen1 , H. J. Jensen3
1
 Risø National Laboratory, Roskilde, Denmark; 2 The Niels Bohr Institute,
Copenhagen, Denmark; 3 PET and Cyclotron Unit, Copenhagen University Hospital,
Denmark.

Aims: The PET-radionuclide 110mIn (T1/2 = 69,1 m) is an interesting alternative for the
widely used SPECT-radionuclide 111In coupled to the precursor DTPA-D-Phe1-
octreotide in the detection of somatostatin receptor-positive neuroendocrine tumors
[1]. 110mIn can be produced either directly via the 110Cd(p,n) 110mIn reaction giving a
mixture of 110mIn and the radionuclidic contaminant 110gIn, or via the decay of 110Sn
(T1/2 = 4,11 h) without any radionuclidic contamination. We have suggested a new
route for the production of 110mIn via the 108Cd(α,2n)110Sn nuclear reaction and the
production of a 110Sn/110mIn isotope generator.
Methods: Excitation functions for the 108Cd(α,2n)110Sn and 108Cd(α,n)111Sn nuclear
reactions have been measured in the α-energy interval 19,9-30,5 MeV by irradiation
of a 70,6% enriched 108Cd metal foil in the Scanditronix MC32-NI cyclotron at
Copenhagen University Hospital. The irradiation was performed at 900 incident beam
angle as an internal irradiation on a water cooled probe with a single natCu monitor
foil in front of the target foil. Both foils were mounted in a special designed
Aluminum target holder which also served as a beam collimator.
Because of inconsistency in the EXFOR database between the sets of tabulated
isomeric ratios and the tabulated cross sections for the 110Cd(p,n) 110m+gIn reactions we
have measured the isomeric ratio at 13,5 MeV proton energy by external irradiation of
a 97,36% enriched 110Cd metal foil. The target foil and a single natTi monitor foil were
irradiated in a Faraday-cup-like target holder.
Results: The measured excitation functions are in good agreement with theoretical
model calculations performed with the computer code ALICE/91. The 110Sn thick
target yield has been calculated from the experimental data resulting in a saturation
activity of approximately 0,8 GBq/µA of 110Sn in the energy interval 30,5-26,4 MeV.
From the measured isomeric ratio the correct set of isomeric ratios in EXFOR has
been determined.
The separation of the produced 110Sn from the target material and the following
110
    Sn/110mIn separation have been done using a modified silica gel column without any
noticeable loss of 110Sn activity (< 1%). The 110Sn/110mIn generator has been produced
and eluted with a typical 110mIn elution yield of 95% and a 110mIn : 110Sn separation
factor of 1 : 2,3 ± 0,2 * 10-6. The eluat has a high radionuclidic purity. The very high
chemical purity of the eluat required in the following labeling procedure has been
confirmed with an ICP-MS analysis.
Conclusion: The suggested production route introduces a new way of producing large
and radionuclidic pure amounts of the PET-radioisotope 110mIn allowing for
exploitation of the isotope generator principle.


[1]:   Lubberink et al., J. Nucl. Med., vol. 43, no. 10, 1391 (2002)

								
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