Cyclotron production of 128Cs (3.62 min). A new positron-emitting radionuclide for medical applications.

The cyclotron production of the short-lived positron emitter 128Cs (3.62 min) from its longer-lived parent 128Ba (2.42 d), based upon the 133Cs(p, 6n) 128Ba leads to 128Cs reaction (Q = -43.98 MeV), has been studied. Cesium-128 has potential applications in positron tomography, particularly for imaging the myocardium and/or for the assessment of regional blood flow. Thick-target yields (mCi/muAh) and cross sections (mb) for 128Ba, 131Ba, 129Cs and 132Cs were measured in the 67-36 MeV proton-energy region. Cyclotron production of 128Ba-128Cs (transient equilibrium) was measured as 3.1 mCi/muAh at end of bombardment (EOB) with a 2.32 g cm-2 thick CsCl target with a proton entrance energy of 67 MeV and exit energy of 54 MeV. Target-radiochemistry using ion-exchange methods allow the preparation of a generator-type system from which high-radionuclidic purity, radiopharmaceutical quality, no-carrier-added 128Cs can be obtained for immediate administration. In addition, with proper radiochemical handling of the 128Ba-128Cs generator, no-carrier-added, high-purity 129Cs (32.35 h, 372 keV, 32%) can also be produced for use in research applications.