• Brelet, Fabien
• Nigron, Etienne
• Tarinas, Maryne
• Audouin, Nadia
• Guertin, Arnaud
• Kamalakannan, Keerthana
• Alliot, Cyrille
• Sounalet, Thomas
• Haddad, Ferid
• Bozovic, Nicolas
• Granger, Lucas
• Dureau, Remy

Abstract

Lead-212 (t1/2 = 10.6 h) and lead-203 (t1/2 = 51.9 h), can be used as a theranostic pair of isotopes for theranostic applications in nuclear medicine. 212Pb can be obtained from ageing 232Th and is used for alpha targeted therapy [1] whereas 203Pb can be produced by proton or deuteron irradiation of a thallium target and allows for single photon emission computed tomography (SPECT) thanks to its 279.2 keV (80.9%) photons. Current production of 203Pb uses natTl bombarded by a proton beam. In this work, we consider alternative production routes using enriched 205Tl and a deuteron beam in order to limit the level of 201Pb (t1/2 = 9.33h) impurities and to avoid the production of 200Pb (t1/2 = 21.5h). Starting from cross section measurements, we have defined optimal production parameters and yields. In parallel, we have developed a manufacturing process of the target by electroplating as well as a separation chemical process using a Pb resin from Triskem. This scheme will allow us to produce 203Pb in the near future.The electrodeposition technique is used to prepare enriched Tl target for both cross section measurements and mass production. A pulse reverse potential is used to reduce Tl+ to Tl on gold substrate. The temperature and pH of the solution are fixed respectively at 20°C and 8. The solution contains EDTA as complexing agent, hydrazine to prevent Tl+ from oxidation to Tl3+ and Brig-35 as surfactant.For the study of 203Pb production cross sections and its impurities, thin deposits of 205Tl (thicknesses ranging from 10 µm and 15 µm) with a circular shape (4 cm2) were made. Experiments were done with a deuteron beam whose energy is ranging from 22 MeV and 34 MeV.For the future routine production, a large deposit of enriched Tl is needed (14 cm2 area) to reduce the heat deposition density. To this end, we are using our rabbit system that accommodate a 15° tilted angle target. A 40 µm thick was successfully obtained with a smooth deposit and good adhesion on gold backing. In parallel, we have studied the chemical separation of Pb/Tl using 203Pb and 202Tl (t1/2 = 12.31 d) obtained by irradiation of thin deposits of natTl (20 µm) with an intensity of 50 nA deuteron beam during 1 h beam. Large Tl targets were dissolved in 1 mol/L of hot nitric acid (70°C) and tracers were added to be able to follow the different species. The solution was first filtered to recover the precipitate of thallium nitrate, which is formed at ambient temperature. The solution was then poured in the column containing the Pb resin previously conditioned with 1 mol/L of HNO3. Tl was recovered by further eluting with 1 mol/L of nitric acid. For the elution of Pb, we studied two methods: the first one corresponds to elution with 0.001 mol/L of nitric acid and the second one with ammonium acetate 1M at pH 7. The recovery of Pb is 83% and 88% respectively with less than 1% of the presence of the impurities of Tl in the solution containing Pb.Our results shows that future routine production of 203Pb using enriched thallium target and deuteron beam is feasible and that the direct elution of 203Pbwith ammonium acetate 1M at pH 7 seems very promising.[1] E. Delpassand, I. Tworowska, R. Esfandiari, J. Torgue, J. D. Hurt, and R. Nunez, “Phase I dose-escalation study of AlphaMedix for targeted-alpha-emitter therapy of PRRT-naive neuroendocrine patients.,” JCO, vol. 39, no. 15_suppl, pp. 4117–4117, May 2021, doi: 10.1200/JCO.2021.39.15_suppl.4117.

Topics

• density
• impedance spectroscopy
• phase
• experiment
• tomography
• laser emission spectroscopy
• gold
• precipitate
• aging
• resin
• electrodeposition
• surfactant
• Thallium
• elution