Production of high purity 47Sc from proton irradiation of natural vanadium targets

BACKGROUND

Scandium-47 is the therapeutic counterpart to the diagnostic radionuclides, 43Sc and 44Sc. Together, these form elementally matched theranostic nuclide pairs, but their incorporation into radiopharmaceuticals requires developing production techniques leading to radioscandium isotopes with high chemical and radionuclidic purity. Previous 47Sc production methods involved expensive, enriched titanium targets that require additional procedures for target recovery. This work investigates the irradiation of natural vanadium targets and the development of purification methods for high-purity 47Sc. Natural vanadium foils were used in cyclotron target configurations. Targets were irradiated with 24 MeV protons at currents of up to 80 µA. A purification method was developed by determining the Kd values of Sc, Cr, and V using MP-50 resin. The final purification method used MP-50 and CM resin columns to isolate the 47Sc from natV and co-produced 51Cr. Inductively Coupled Plasma Mass Spectrometry (ICP-MS), gamma-ray spectroscopy, and a DOTA titration were used to characterize the 47Sc product.

RESULTS

Two cyclotron targets were designed, a small-scale target for developing a purification procedure and a high-power target for scaled-up production. The high-power target maximum current was 80 µA of 24 MeV protons. The yield for an 8 h irradiation at 80 µA of 24 MeV protons, was 128.02 ± 11.1 MBq of 47Sc at End of Bombardment. The radionuclidic purity of 47Sc was 99.5 ± 0.2%. The purification using MP-50 and CM columns resulted in the removal of natV target and 51Cr contaminate in the final 47Sc product, with an average recovery of 72 ± 2.1% and a DOTA apparent molar activity of 7733 ± 155 MBq/µmol. ICP-MS results showed that all top-row transition metals were below the limit of detection (< 1 ppb) with the exception of Zn, which was 64.6 ± 10.3 ppb.

CONCLUSIONS

A high-power cyclotron target capable of withstanding a proton current of 80 µA was developed. A novel separation method was developed for isolating the 47Sc from the vanadium target and the co-produced 51Cr contaminate. The final product characterization resulted in a chemically and radionuclidically pure 47Sc product with high recovery yields.

Production and radiochemical separation of Tb-161 as a feasible beta therapeutic radioisotope from reactor irradiated Gd target

Terbium-161 (161Tb) is a promising therapeutic radionuclide that has gained significant attention in the field of nuclear medicine in recent years. 161Tb has several favorable characteristics that make it a valuable candidate for targeted radionuclide therapy. The production of No-carrier-added 161Tb was carried out by the neutron activation of natural gadolinium target in the Egyptian Second Research Reactor (ETRR-2) at a thermal neutron flux position of 1.8 × 1014 ncm-2s-1. The radioactivities of 161Tb as well as coproduced Gd radioimpurities were computed theoretically by the MCNPX2.7.0 code and verified by actual measurements, where accepted discrepancies were obtained. The purification of 161Tb from irradiated Gd target was developed by Chelex-100 resin. The elution performance was studied using different eluents, and 0.1 M HNO3 was found to be the best medium to obtain a high separation efficiency of more than 92% in a short time. The eluted 161Tb was of high chemical, radiochemical, and radionuclidic purities, indicating its potential for effective application in radiopharmaceutical preparation.

Towards Clinical Development of Scandium Radioisotope Complexes for Use in Nuclear Medicine: Encouraging Prospects with the Chelator 1,4,7,10-Tetraazacyclododecane-1,4,7,10-tetraacetic Acid (DOTA) and Its Analogues

Scandium (Sc) isotopes have recently attracted significant attention in the search for new radionuclides with potential uses in personalized medicine, especially in the treatment of specific cancer patient categories. In particular, Sc-43 and Sc-44, as positron emitters with a satisfactory half-life (3.9 and 4.0 h, respectively), are ideal for cancer diagnosis via Positron Emission Tomography (PET). On the other hand, Sc-47, as an emitter of beta particles and low gamma radiation, may be used as a therapeutic radionuclide, which also allows Single-Photon Emission Computed Tomography (SPECT) imaging. As these scandium isotopes follow the same biological pathway and chemical reactivity, they appear to fit perfectly into the "theranostic pair" concept. A step-by-step description, initiating from the moment of scandium isotope production and leading up to their preclinical and clinical trial applications, is presented. Recent developments related to the nuclear reactions selected and employed to produce the radionuclides Sc-43, Sc-44, and Sc-47, the chemical processing of these isotopes and the main target recovery methods are also included. Furthermore, the radiolabeling of the leading chelator, 1,4,7,10-tetraazacyclododecane-1,4,7,10-tetraacetic acid (DOTA), and its structural analogues with scandium is also discussed and the advantages and disadvantages of scandium complexation are evaluated. Finally, a review of the preclinical studies and clinical trials involving scandium, as well as future challenges for its clinical uses and applications, are presented.

Potential production of Ac-225 at Egyptian second research reactor (ETRR-2) through neutron induced transmutation of Ra-226

A considerable focus has been paid to the production of 225Ac due to its effective therapeutic action in alpha-targeted radiotherapy. Considering the future global clinical demand, it is necessary to increase the production capacity of 225Ac. A feasibility study was conducted to investigate the production of 225Ac through neutron induced transmutation of 226Ra at the Egyptian Second Research Reactor (ETRR-2) using the MCNPX code. The calculations were carried out for 1 g of 226Ra target exposed to the highest neutron flux in the irradiation grid surrounding the reactor core. The 227Ra, 225Ra, 227Ac, and 225Ac generated activities as a function of irradiation and decay times were estimated. Our study revealed that in this non-linear production process, 39.22 MBq of pure 225Ac could be obtained after three days of irradiation, while 148.74 MBq could be obtained after fifteen days of continuous irradiation.

Radiometals in Imaging and Therapy: Highlighting Two Decades of Research

The present article highlights the important progress made in the last two decades in the fields of molecular imaging and radionuclide therapy. Advancements in radiometal-based positron emission tomography, single photon emission computerized tomography, and radionuclide therapy are illustrated in terms of their production routes and ease of radiolabeling. Applications in clinical diagnostic and radionuclide therapy are considered, including human studies under clinical trials; their current stages of clinical translations and findings are summarized. Because the metalloid astatine is used for imaging and radionuclide therapy, it is included in this review. In regard to radionuclide therapy, both beta-minus (β-) and alpha (α)-emitting radionuclides are discussed by highlighting their production routes, targeted radiopharmaceuticals, and current clinical translation stage.

Radioactive nuclei for β + γ PET and theranostics: selected candidates

Positron emission tomography (PET) is an established medical diagnostic imaging method. Continuous improvements are aimed at refining image reconstruction, reducing the amount of radioactive tracer and combining with targeted therapy. Time-of-flight (TOF)-PET provides the localization of the tracer through improved time resolution, nuclear physics may contribute to this goal via selection of radioactive nuclei emitting additional γ-rays. This additional radiation, when properly detected, localizes the decay of the tracer at the line of response (LoR) determined by two detected 511 keV quanta. Selected candidates are presented. Some are particularly interesting, as they are strong candidates for theranostic applications.

Separation of 44Sc from 44Ti in the Context of A Generator System for Radiopharmaceutical Purposes with the Example of [44Sc]Sc-PSMA-617 and [44Sc]Sc-PSMA-I&T Synthesis

Today, ⁴⁴Sc is an attractive radionuclide for molecular imaging with PET. In this work, we evaluated a ⁴⁴Ti/⁴⁴Sc radionuclide generator based on TEVA resin as a source of ⁴⁴Sc. The generator prototype (5 MBq) exhibits high ⁴⁴Ti retention and stable yield of ⁴⁴Sc (91 ± 6 %) in 1 mL of eluate (20 bed volumes, eluent—0.1 M oxalic acid/0.2 M HCl) during one year of monitoring (more than 120 elutions). The breakthrough of ⁴⁴Ti did not exceed 1.5 × 10⁻⁵% (average value was 6.5 × 10⁻⁶%). Post-processing of the eluate for further use in radiopharmaceutical synthesis was proposed. The post-processing procedure using a combination of Presep^® PolyChelate and TK221 resins made it possible to obtain ⁴⁴Sc-radioconjugates with high labeling yield (≥95%) while using small precursor amounts (5 nmol). The proposed method takes no more than 15 min and provides ≥90% yield relative to the ⁴⁴Sc activity eluted from the generator. The labeling efficiency was demonstrated on the example of [⁴⁴Sc]Sc-PSMA-617 and [⁴⁴Sc]Sc-PSMA-I&T synthesis. Some superiority of PSMA-I&T over PSMA-617 in terms of ⁴⁴Sc labeling efficiency was demonstrated (likely due to presence of DOTAGA chelator in the precursor structure). It was also shown that microwave heating of the reaction mixture considerably shortened the reaction time and improved radiolabeling yield and reproducibility of [⁴⁴Sc]Sc-PSMA-617 and [⁴⁴Sc]Sc-PSMA-I&T synthesis.

Production of scandium radionuclides for theranostic applications: towards standardization of quality requirements

In the frame of "precision medicine", the scandium radionuclides have recently received considerable interest, providing personalised adjustment of radiation characteristics to optimize the efficiency of medical care or therapeutic benefit for particular groups of patients. Radionuclides of scandium, namely scandium-43 and scandium-44 (43/44Sc) as positron emitters and scandium-47 (47Sc), beta-radiation emitter, seem to fit ideally into the concept of theranostic pair. This paper aims to review the work on scandium isotopes production, coordination chemistry, radiolabeling, preclinical studies and the very first clinical studies. Finally, standardized procedures for scandium-based radiopharmaceuticals have been proposed as a basis to pave the way for elaboration of the Ph.Eur. monographs for perspective scandium radionuclides.

Synthesis of chitosan-acrylic acid/multiwalled carbon nanotubes composite for theranostic 47Sc separation from neutron irradiated titanium target

A simple and efficient separation method of carrier-free ⁴⁷Sc from neutron irradiated titanium target using a novel chitosan-acrylic acid/multiwalled carbon nanotubes (CS-AA/MWCNTs) composite was established. The synthesis of the CS-AA/MWCNTs composite was achieved using gamma radiation-induced template polymerization. The grafting efficiency (GE%) of AA on CS onto the surface of f-MWCNTs reached a maximum of~84% under the optimized conditions (30 wt% CS, 1.0 wt% AA, 0.15 wt% f-MWCNTs, >0.2 wt% N,N'-Methylenebisacrylamide (NMBA), and irradiation dose ~25 kGy). Different analyses (FT-IR, SEM, TGA and DTA) were examined for confirming the structural morphology and mechanical properties of the new synthesized composite. Interestingly, the CS-AA/MWCNTs composite depicted a selective adsorption of Sc(III) rather than Ti(IV) ions at pH 5 with adsorption efficiency of ~93.93%. The ionic exchange separation of no-carrier-added (NCA)⁴⁷Sc(III) from irradiated TiO₂ target on CS-AA/MWCNTs composite packed column efficiently eluted ⁴⁷Sc(III) by 91 ± 0.8% using 1 M HCl solution. The quality control tests (radionuclidic, radiochemical, and chemical purities) for the eluted ⁴⁷Sc(III) clarified its high purity and validity for cancer theranostics.