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


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

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

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
    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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