Speaker
Summary
For the treatment of micrometastatic or disseminated cancers, radiopharmaceuticals with high Linear Energy Transfert (LET) radiations, such as Auger Electron emitters (AEs), show potential in preclinical studies [Kassis, 2003]. Fundamental radiation biology studies on effects of AEs require a pure AE-emitting radionuclide, with minimal associated medium/high energy electron or photon emissions. To this end, 165Er is a promising radionuclide. It emits 7 AEs per decay [ICRP 107] with only associated X-rays emission. There are several possible production routes among which one of the most promising routes is the indirect production through 165Ho(α,4n)165Tm reaction that allows to make a 165Tm/165Er generator (T1/2 = 30.06 h/10.36 h). Moreover, the naturally monoisotopic target allows to limit co-productions by adapting beam energy. From that, it makes possible to reach better Apparent Molar Activity (AMA) mandatory for dosimetry studies.
In a project including also aspects of chemical separations and radiolabeling tests, a focus on productions with the 165Ho(α,x) reactions using a 68 MeV alpha beam from the GIP ARRONAX C70 XP cyclotron will be presented. Firstly, cross-sections measurements were performed using the stacked foil technique to consolidate the shape of the excitation function, which could show some discrepancies between existing values. Beam intensity has been obtained using an instrumented Faraday cup. Absolute cross-sections were also measured for the monitor reactions natAl(α,x)22Na,24Na. These values acquired between 38 and 67 MeV allow us to establish theoretical estimations of AMA values under thick-target irradiation conditions. In a second phase, thick target (50 µm) production were carried out.
The cross-section measurements performed for the 165Ho(a,xn) reactions are in agreement with recent cross-section data. The maximum production cross-section of 165Tm is around 1200 mb at 50 MeV. Thick target (50 µm) productions were carried out at an incident energy of 58 MeV, limiting the production of 166Tm and enhancing the 166Er/165Er ratio. The 165Tm activities produced for 14 µA.h are 93 MBq. A theoretical calculation based on these measured cross-section values gives a production of 125 MBq. This difference of 25% can be explained by the overestimation of the current measurement of our high-intensity irradiation device and by the losses of the recoil nuclei. Without considering the efficiency of chemical separation, the radiological purity of 165Er would be 100%. After a chemical separation to isolate the thulium completed End Of Beam (EOB) plus 2h and an 8h 165Tm/165Er generator cycle, the calculated AMA is minimum for the 1st elution (EOB+10h) with 1.9 103 MBq/nmol for 50 MeV and 2.4 103 MBq/nmol for 56 MeV.
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