Abstract The development of a highly efficient resonance ionization scheme for lutetium is presented. A laser ion source, based on the all-solid-state Titanium:sapphire laser system, was used at the 30 keV RISIKO off-line mass separator to characterize different possible optical excitation schemes in respect to their ionization efficiency. The developed laser resonance ionization scheme can be directly applied to the use at radioactive ion beam facilities, e. g. at the CERN-MEDICIS facility, for large-scale production of medical radioisotopes.

Measurement of the laser resonance ionization efficiency for lutetium

The β--particle-emitting erbium-169 is a potential radionuclide toward therapy of metastasized cancer diseases. It can be produced in nuclear research reactors, irradiating isotopically-enriched 168Er2O3. This path, however, is not suitable for receptor-targeted radionuclide therapy, where high specific molar activities are required. In this study, an electromagnetic isotope separation technique was applied after neutron irradiation to boost the specific activity by separating 169Er from 168Er targets. The separation efficiency increased up to 0.5% using resonant laser ionization. A subsequent chemical purification process was developed as well as activity standardization of the radionuclidically pure 169Er. The quality of the 169Er product permitted radiolabeling and pre-clinical studies. A preliminary in vitro experiment was accomplished, using a 169Er-PSMA-617, to show the potential of 169Er to reduce tumor cell viability.

/pdf/production-of-mass-separated-erbium-169-towards-the-first-4whsilz4ay.pdf

Production of Mass-Separated Erbium-169 Towards the First Preclinical in vitro Investigations.

Resonance ionization mass spectroscopy is employed in a time of flight mass spectrometer to explore atomic structure of lutetium in continuum using three- step photoionization. Nineteen new odd parity autoionization levels of neutral lutetium are identified in the range 50650 – 51650 cm−1 above ground level. The work provides three photon ionization pathways for neutral lutetium with all transitions in the visible range.

Odd parity autoionization levels of Lu I by three-step photoionization

Abstract Terbium-149 (T 1/2 = 4.1 h, E α = 3.98 MeV (16.7%), 28 µm range in tissue) is a radionuclide with potential for targeted alpha therapy. Due to the negligible emission of α-emitting daughter nuclides, toxicity to healthy tissue may be reduced in comparison with other α-particle emitters. In this study, terbium-149 was produced via 1.4 GeV proton irradiation of a tantalum target at the CERN-ISOLDE facility. The spallation products were mass separated and implanted on zinc-coated foils and, later, radiochemically processed. Terbium-149 was separated from the co-produced isobaric radioisotopes and the zinc coating from the implantation foil, using cation-exchange and extraction chromatographic techniques, respectively. At the end of separation, up to 260 MBq terbium-149 were obtained with &gt; 99% radionuclidic purity. Radiolabeling experiments were performed with DOTATATE, achieving 50 MBq/nmol apparent molar activity with radiochemical purity &gt; 99%. The chemical purity was determined by inductively coupled plasma–mass spectrometry measurements, which showed lead, copper, iron and zinc only at ppb level. The radiolabeling of the somatostatin analogue DOTATATE with [ 149 Tb]TbCl 3 and the subsequent in vivo PET/CT scans conducted in xenografted mice, showing good tumor uptake, further demonstrated product quality and its ability to be used in a preclinical setting. 

Terbium-149 production: a focus on yield and quality improvement towards preclinical application

Ion sources exploiting laser resonance ionization offer efficient and element-selective radioactive ion beam production at the leading isotope separation on-line facilities worldwide. Most commonly, laser resonance ionization takes place inside a resistively heated atomizer tube directly coupled to the production target, where the element of interest is evaporated and provided as atomic vapor. While naturally the majority of atoms is ionized inside this hot cavity, a fraction of the neutrals effuses towards the high voltage beam extraction system of the subsequent mass separator. We report on several systematic investigations on this phenomenon regarding its significance and implications on the operation of resonance ionization laser ion sources. Experiments suggest a less sharply directed atom cone than expected from theoretical model, up to a lateral opening angle of 45°. Inside the tubular volume defined by the laser beam diameter around the central axis behind the source exit, more than 90% of potentially ionizable atoms are found within the first 2 cm. Geometrical constraints for the construction of devices based on ionization in the effusing atom beam directly downstream of the hot cavity are derived, and causes for cross-mass beam contamination are identified. Counter measures using laser repetition rate synchronized beam gating by fast electrostatic beam deflection to overcome these problems are presented.

Atom beam emersion from hot cavity laser ion sources

The MEDICIS-PROMED Innovative Training Network under the Horizon 2020 EU program aims to establish a network of early stage researchers, involving scientific exchange and active cooperation between leading European research institutions, universities, hospitals, and industry. Primary scientific goal is the purpose of providing and testing novel radioisotopes for nuclear medical imaging and radionuclide therapy. Within a closely linked project at CERN, a dedicated electromagnetic mass separator system is presently under installation for production of innovative radiopharmaceutical isotopes at the new CERN-MEDICIS laboratory, directly adjacent to the existing CERN-ISOLDE radioactive ion beam facility. It is planned to implement a resonance ionization laser ion source (RILIS) to ensure high efficiency and unrivaled purity in the production of radioactive ions. To provide a highly efficient ionization process, identification and characterization of a specific multi-step laser ionization scheme for each individual element with isotopes of interest is required. The element lutetium is of primary relevance, and therefore was considered as first candidate. Three two-step excitation schemes for lutetium atoms are presented in this work, and spectroscopic results are compared with data of other authors.

/pdf/laser-resonance-ionization-spectroscopy-on-lutetium-for-the-13lyu7rlmw.pdf

Laser resonance ionization spectroscopy on lutetium for the MEDICIS project

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Laser resonance ionization spectroscopy on lutetium for the MEDICIS project