Molybdenum-99 production pathways and the sorbents for 99Mo/99mTc generator systems using (n, γ) 99Mo: a review

How green are radiopharmaceutical sciences?

The rapid growth of radiopharmaceutical sciences, driven by regulatory approvals of theranostic agents and the expanding role of PET imaging, underscores the need for sustainable and green practices. While radiopharmaceuticals offer high precision and targeted therapy with minimal systemic toxicity, the field faces challenges related to increasing demand, energy consumption, and waste management. The nuclear medicine market is projected to reach $30 billion by 2030, necessitating the integration of sustainability principles such as green chemistry and green engineering into radiopharmaceutical development. Given the energy-intensive nature of radiochemical processes, these principles provide strategies for reducing environmental impact. However, radiopharmaceutical sciences require adaptations to traditional sustainability frameworks due to factors like radiation safety, speed, and automation. This perspective examines the applicability of the 12 principles of green chemistry and engineering, proposing nine key principles tailored to radiopharmaceutical sciences. These principles address waste prevention, radionuclide recycling, energy efficiency, and the adoption of cleaner irradiation technologies. As the field evolves, incorporating sustainability into training programs and research initiatives will be essential.

99mTc-Labeled Quinolone-Based Novel Skeletal Tracers for Tumor Visualization through Fibroblast Activation Protein

Fibroblast activation protein (FAP) has emerged as a prominent target for tumor diagnosis. Quinoline-based FAP PET tracers demonstrated clinical feasibility. However, there is a relative scarcity of clinical studies on 99mTc-labeled FAP SPECT tracers. The existing quinoline-derived 99mTc-FAPI tracer exhibits relatively low tumor uptake and suboptimal pharmacokinetic properties, which restrict its clinical application. Consequently, it is necessary to alter the pharmacophores to improve its druggability. In this study, a novel quinolone-based pharmacophore was developed by utilizing scaffold hopping and conformational constrained strategies. Serial screening and preclinical evaluations were conducted. The 99mTc-FAPI-YQ3 showed extremely high tumor uptake and excellent pharmacokinetic properties. Additionally, 99mTc-FAPI-YQ3 demonstrated reliable safety characteristics and clinical efficacy on four different oncology patients. In conclusion, 99mTc-FAPI-YQ3 was a promising radiotracer for FAP-targeted cancer diagnosis, shedding light on substantially advancing SPECT molecular imaging.

Development of Porous MoO2 Pellet Target for 99Mo/99mTc Generator

Technetium-99m(99mTc) is used worldwide in 85% of nuclear medicine diagnostic imaging procedures. We developed porous MoO2 pellets as an alternative to reactor-based targets in an (n,γ) reaction for producing Technetium-99m (99mTc) in nuclear medicine. The pellets, formed through a manufacturing process involving mixing, sintering, eluting, and drying, offer advantages such as selective dissolution and improved yield. This research offers a potential solution for stable 99mTc production, focusing on porous molybdenum dioxide (MoO2) as a target material due to its insolubility in water. Using potassium molybdate (K2MoO4) as a pore former, we developed porous MoO2 pellets that facilitate efficient technetium extraction and target recycling. This approach offers control over pore formation and shows promise in addressing supply challenges and enhancing 99mTc production.

Green synthesis of alumina nanoparticle using Hibiscus rosa-sinensis leaf extract as a candidate for molybdenum-99 adsorbent

Al₂O₃ nanoparticle is effectively used as an adsorbent for the low specific activity of molybdenum-99 (⁹⁹Mo). The Al₂O₃ nanoparticle was synthesized by the green synthesis method using Hibiscus rosa-sinensis leaf extract (HRE). The Al₂O₃ nanoparticle synthesized using 10% of the HRE has a crystallite size of 4.9 nm, a surface area of 254.6 m²/g, a pore size of 9.1 nm, a pore volume of 0.58 cm³/g and has a Mo adsorption capacity of 43.4 ± 6.1 mg Mo/g.

Dissolution of Molybdenum in Hydrogen Peroxide: A Thermodynamic, Kinetic and Microscopic Study of a Green Process for 99mTc Production

^99mTc-based radiopharmaceuticals are the most commonly used medical radioactive tracers in nuclear medicine for diagnostic imaging. Due to the expected global shortage of ⁹⁹Mo, the parent radionuclide from which ^99mTc is produced, new production methods should be developed. The SORGENTINA-RF (SRF) project aims at developing a prototypical medium-intensity D-T 14-MeV fusion neutron source specifically designed for production of medical radioisotopes with a focus on ⁹⁹Mo. The scope of this work was to develop an efficient, cost-effective and green procedure for dissolution of solid molybdenum in hydrogen peroxide solutions compatible for ^99mTc production via the SRF neutron source. The dissolution process was extensively studied for two different target geometries: pellets and powder. The first showed better characteristics and properties for the dissolution procedure, and up to 100 g of pellets were successfully dissolved in 250-280 min. The dissolution mechanism on the pellets was investigated by means of scanning electron microscopy and energy-dispersive X-ray spectroscopy. After the procedure, sodium molybdate crystals were characterized via X-ray diffraction, Raman and infrared spectroscopy and the high purity of the compound was established by means of inductively coupled plasma mass spectroscopy. The study confirmed the feasibility of the procedure for production of ^99mTc in SRF as it is very cost-effective, with minimal consumption of peroxide and controlled low temperature.

Future development of global molybdenum-99 production and saving of atmospheric radioxenon emissions by using nuclear fusion-based approaches

Technetium-99m, the decay product of molybdenum-99, is the most used medical isotope in diagnostic imaging. The future disruptions of molybdenum-99 supply, due to the final shut down of some old producing reactors, has led some current global supplies to plan the expansion of their production capacity. While other countries are developing own production facilities to supply their domestic demand. The global increase of molybdenum-99 production in the coming years could increase by about five times the current demand, with about the 50 percent of additional production in North America. Xenon radionuclides are an inevitable by-product of the nuclear plants production, and their periodically release into the atmosphere, contribute to the background that is also revealed by the IMS stations of the CBTO treaty. In this framework, the development of new technologies, posing no risk in relation to nuclear proliferation and do not result in emissions of radioxenon, could mitigate the issues related to the forecast increase of molybdenum-99 production worldwide. In Italy, an alternative 99Mo production project, the project ENEA Sorgentina, based on the irradiation of molybdenum by neutrons produced by a deuterium-tritium nuclear fusion process, is under development. This facility will not release radioxenon into the atmosphere, so it will not affect the background value in the atmosphere in Southern Europe.

Discovery, nuclear properties, synthesis and applications of technetium-101

Technetium-101 (101Tc) has been poorly studied in comparison with other Tc isotopes, although it was first identified over ~80 years ago shortly after the discovery of the element Tc itself. Its workable half-life and array of production modes, i.e., light/heavy particle reactions, fission, fusion-evaporation, etc., allow it to be produced and isolated using an equally diverse selection of chemical separation pathways. The inherent nuclear properties of 101Tc make it important for research and applications related to radioanalytical tracer studies, as a fission signature, fusion materials, fission reactor fuels, and potentially as a radioisotope for nuclear medicine. In this review, an aggregation of the known literature concerning the chemical, nuclear, and physical properties of 101Tc and some its applications are presented. This work aims at providing an up-to-date and first-of-its-kind overview of 101Tc that could be of importance for further development of the fundamental and applied nuclear and radiochemistry of 101Tc.

Evaluating the Sorption Affinity of Low Specific Activity 99Mo on Different Metal Oxide Nanoparticles

99Mo/99mTc generators are mainly produced from 99Mo of high specific activity generated from the fission of 235U. Such a method raises proliferation concerns. Alternative methods suggested the use of low specific activity (LSA) 99Mo to produce 99mTc generators. However, its applicability is limited due to the low adsorptive capacity of conventional adsorbent materials. This study attempts to investigate the effectiveness of some commercial metal oxides nanoparticles as adsorbents for LSA 99Mo. In a batch equilibration system, we studied the influence of solution pH (from 1–8), contact time, initial Mo concentration (from 50–500 mg∙L−1), and temperature (from 298–333 K). Moreover, equilibrium isotherms and thermodynamic parameters (changes in free energy ΔG0, enthalpy change ΔH0, and entropy ΔS0) were evaluated. The results showed that the optimum pH of adsorption ranges between 2 and 4, and that the equilibrium was attained within the first two minutes. In addition, the adsorption data fit well with the Freundlich isotherm model. The thermodynamic parameters prove that the adsorption of molybdate ions is spontaneous. Furthermore, some investigated adsorbents showed maximum adsorption capacity ranging from 40 ± 2 to 73 ± 1 mg Mo∙g−1. Therefore, this work demonstrates that the materials used exhibit rapid adsorption reactions with LSA 99Mo and higher capacity than conventional alumina (2–20 mg Mo∙g−1).

New strategies for a sustainable 99mTc supply to meet increasing medical demands: Promising solutions for current problems

The continuing rapid expansion of ^99mTc diagnostic agents always calls for scaling up ^99mTc production to cover increasing clinical demand. Nevertheless, ^99mTc availability depends mainly on the fission-produced ⁹⁹Mo supply. This supply is seriously influenced during renewed emergency periods, such as the past ⁹⁹Mo production crisis or the current COVID-19 pandemic. Consequently, these interruptions have promoted the need for ^99mTc production through alternative strategies capable of providing clinical-grade ^99mTc with high purity. In the light of this context, this review illustrates diverse production routes that either have commercially been used or new strategies that offer potential solutions to promote a rapid production growth of ^99mTc. These techniques have been selected, highlighted, and evaluated to imply their impact on developing ^99mTc production. Furthermore, their advantages and limitations, current situation, and long-term perspective were also discussed. It appears that, on the one hand, careful attention needs to be devoted to enhancing the ⁹⁹Mo economy. It can be achieved by utilizing ⁹⁸Mo neutron activation in commercial nuclear power reactors and using accelerator-based ⁹⁹Mo production, especially the photonuclear transmutation strategy. On the other hand, more research efforts should be devoted to widening the utility of ⁹⁹Mo/^99mTc generators, which incorporate nanomaterial-based sorbents and promote their development, validation, and full automization in the near future. These strategies are expected to play a vital role in providing sufficient clinical-grade ^99mTc, resulting in a reasonable cost per patient dose.

Evaluating the intensity of the 'prompt' 140.5 keV γ-ray of 99Mo using a 4παβ(LS)-γ(HPGe) measurement system

The absolute intensity for the 'prompt' 140.5 keV gamma-ray of ⁹⁹Mo was evaluated using the β-γ coincidence technique. A liquid sample of ⁹⁹Mo was prepared from a⁹⁹Mo/^99mTc generator and measured in a 4παβ(LS)-γ(HPGe) system that comprises a Liquid Scintillator (LS) detector and a High-Purity Germanium (HPGe) detector. The sample was introduced into scintillation fluid embedded in a photo-reflector assembly that provides almost 100% efficiency for detecting β particles (in the energy range of intreset). The combination of the HPGe and the LS detectors provided a highly effective rejection mechanism for non-coincident events. Thereby, the distinction between the detected 140.5 keV events originating from decays of ^99mTc (IT) and those from transitions bypassing the metastable state could be obtained and the 'prompt' intensity was evaluated directly. The system was calibrated for detecting β particles and γ-rays using radioactive sources of known activities and having identical geometry as the sample containing ⁹⁹Mo. The absolute intensity of the 'prompt' 140.5 keV was found to be (5.21 ± 0.02_stat±0.16_sys)%, in good agreement with results from more recently reported works.

Surface modification of acid-functionalized mesoporous gamma-alumina for non-fission 99Mo/99mTc generator

Mesoporous gamma-alumina (MGA) was synthesized for neutron-activated ⁹⁹Mo adsorbent. Acid functionalization of the MGA was carried out to enhance the Mo adsorption capacity and the ⁹⁹Mo breakthrough profile. The acid-treated MGA has a more positive particle charge, rougher surface, smaller particle and pore size, larger surface area, and wider pore distance. The acid-treated MGA has a Mo adsorption capacity of 82.8 ± 6.3 mg Mo/g and resulted in ^99mTc eluate with the ⁹⁹Mo breakthrough at the acceptable level.

Radiolabeled nanomaterials for biomedical applications: radiopharmacy in the era of nanotechnology

BACKGROUND

Recent advances in nanotechnology have offered new hope for cancer detection, prevention, and treatment. Nanomedicine, a term for the application of nanotechnology in medical and health fields, uses nanoparticles for several applications such as imaging, diagnostic, targeted cancer therapy, drug and gene delivery, tissue engineering, and theranostics.

RESULTS

Here, we overview the current state-of-the-art of radiolabeled nanoparticles for molecular imaging and radionuclide therapy. Nanostructured radiopharmaceuticals of technetium-99m, copper-64, lutetium-177, and radium-223 are discussed within the scope of this review article.

CONCLUSION

Nanoradiopharmaceuticals may lead to better development of theranostics inspired by ingenious delivery and imaging systems. Cancer nano-theranostics have the potential to lead the way to more specific and individualized cancer treatment.

Practicality of hierarchically macro/mesoporous γ-Al2O3 as a promising sorbent in the preparation of low specific activity 99Mo/99mTc generator

Hierarchically macro-/mesoporous γ-Al₂O₃ (HMMA) was synthesized and characterized by various analytical techniques. The results indicated that HMMA possessed macropores (∼0.45 μm) and mesopores (∼10.6 nm) with a large surface area (∼542 m² g^-1). The absorption behaviors of Mo and Re with HMMA were investigated. The maximum static absorption capacity could reach about 250 mg Mo per g HMMA. The absorption equilibrium can be attained quickly within 10 mins. At initial Mo ions concertation of 10,000 mg L^-1, the breakthrough capacity was determined to be around 200 mg Mo per g HMMA. Additional, absorption mechanism results indicated that Mo ions reacts strongly with a hydroxyl on the surface of γ-Al₂O₃ and an adjacent Al atom, simultaneously. A 9.15 mCi (339 MBq) ⁹⁹Mo generator was prepared and evaluated its performance for over one week. The recovery of ^99mTc could reach about 89% with favorable radionuclidic, radiochemical and chemical purity for nuclear medicine application. HMMA has a potential application prospect for the preparation of low specific activity (LSA) ⁹⁹Mo/^99mTc generator.

A semi-automated module for the separation and purification of 99mTc from simulated molybdenum target

A semi-automated purification module for the cyclic separation of 99mTc was designed for production of [99mTc]TcO4– from γ irradiated 100Mo target. The separation process was carried out by using a 3-column purification system and the final product, [99mTc]TcO4–, was obtained in a total volume of 7 mL. To confirm proper separation achieved for 99mTc, a radio-labeling procedure using DTPA chelator was performed. The radiochemical purity was higher than 95%, which meets the strict radiopharmaceutical requirements. The yielded 99mTc can be separated with high efficiency from Mo in a quick and repeated way. Loss of 99mTc radioactivity during such a three-column separation process was not larger than 10%.