An alternative radiochemical separation strategy for isolation of Ac and Ra isotopes from high energy proton irradiated thorium targets for further application in Targeted Alpha Therapy (TAT).

Targeted Alpha Therapy (TAT) has shown very high potential for the treatment of cancers that were not responsive to other therapy options (e.g., ß- therapy and chemotherapy). The main constraint to the widespread use of TAT in clinics is the limited availability of alpha-emitting radionuclides. One of the most promising candidates for TAT is 225Ac (t1/2 = 9.92 days), which can be used directly in combination with selective biomolecules (e.g., antibodies, peptides, etc.) or be a generator source of 213Bi (t1/2 = 45.6 min), another shorter-lived TAT radionuclide. Several strategies are currently under investigation to increase the supply of 225Ac. One of the most attractive options is the irradiation of natural thorium-232 targets with high-energy protons (≥100 MeV). However, there are several challenges associated with this production method including the development of an efficient radiochemical purification method. During irradiation of natural thorium with proton energy above 100 MeV, several Ra isotopes (223,224,225Ra) are produced. 223Ra (t1/2 = 11.43 days) is used for the treatment of bone metastases and can also be used as a generator source for 211Pb. Additionally, 225Ra (t1/2 = 14.9 days) can be a valuable source of isotopically pure 225Ac. In the present work, we address the radiochemical separation aspects of isolating Ac and Ra isotopes from irradiated thorium targets.

Improved separation scheme for 44Sc produced by irradiation of natCa targets with 12.8 MeV protons.

INTRODUCTION: 44Sc is of great interest as a positron emission tomography (PET) radionuclide due to its suitable nuclear characteristics: Eß+max = 1.47 MeV, branching ratio 94.3% and convenient half-life of 3.97 h. Here, 44Sc was produced via the widely used reaction 44Ca (p,n)44Sc using natural calcium as a target. METHODS: The irradiation was performed at TRIUMF using the 13 MeV cyclotron. The separation consisted of a combination of DGA branched resin and Dowex 50Wx8 (200-400 mesh). The distribution coefficients of Sc3+ on Dowex 50Wx8 (NH4+ form, 200-400 mesh) with ammonium α-hydroxyisobutyrate (pH = 4.8) medium were determined in this study. RESULTS AND CONCLUSION: The tested scheme allows both a reliable separation of 44Sc from the target material as well as from the other competitive metals and a final fraction with high specific activity. The achieved radiochemical yield was 95 ± 3%.