Proton and deuteron cyclotron production of the beta-gamma emitter rhenium-186g for metabolic radiotherapy and spet : RENIO experiment of INFN GR-V

Excitation functions, thin- and thick-target yields (tty and TTY) for the 181-186Re radionuclides have been measured with the activation method on stacked natural W foils for proton energies up to 22 MeV and deuteron energies up to 19 MeV. Besides, TTYs obtained irradiating highly enriched W-186 targets were measured. These results are compared both with the experimental literature values and the ones calculated by the EMPIRE II code. In particular, the attention is focused on Re-186g due to its remarkable applications in nuclear medicine for metabolic radiotherapy of tumors. The 186gRe is a B/y emitter presently used in metabolic radiotherapy and with optimal perspectives to be used in radioimmunotherapy (RIT) too, thanks to its suitable nuclear properties. In particular the energy range of the B particles suggests that this radionuclide is a good candidate for cancers with small dimensions (from few millimeters to a few centimeters). The possibility to use this radionuclide for therapeutic purposes is strictly linked to the possibility of increase its specific activity AS. This improvement is reached by substituting the common 185Re(n,y) production route with the 186W(p,n) or (d,2n) cyclotron production ones, due to the possibility of radiochemical separation of the product from the target in no-carrier-added form (NCA). The excitation functions were measured by using the stacked-foil technique, while the experimental TTYs were measured by using thick W-186 pressed powdered slabs in order to guarantee the total proton beam absorption. As regard the cross-section, the stack of foils consisted of alternating aluminum (as energy degrader and catcher foils), W, and Ti beam monitor foils. All the irradiations have been carried out with the cyclotron (K=38) of JRC- Ispra at different energies. We can note that there is a pretty good agreement between the data obtained irradiating natW and the one obtained from an highly enriched target. A selective radiochemical separation of radio-Re from irradiated W target and radio-Ta by-products was set up.