Charged particle induced reaction cross section data for production of the emerging medically important positron emitter64Cu: A comprehensive evaluation

From cyclotrons to chromatography and beyond: a guide to the production and purification of theranostic radiometals

Recent clinical success with metal-based radiopharmaceuticals has sparked an interest in the potential of these drugs for personalized medicine. Although often overlooked, the success and global impact of nuclear medicine is contingent upon the purity and availability of medical isotopes, commonly referred to as radiometals. For nuclear medicine to reach its true potential and change patient lives, novel production and purification techniques that increase inventory of radiometals are desperately needed. This tutorial review serves as a resource for those both new and experienced in nuclear medicine by providing a detailed explanation of the foundations for the production and purification of radiometals, stemming from nuclear physics, analytical chemistry, and so many other fields, all in one document. The fundamental science behind targetry, particle accelerators, nuclear reactors, nuclear reactions, and radiochemical separation are presented in the context of the field. Finally, a summary of the latest breakthroughs and a critical discussion of the threats and future potential of the most utilized radiometals is also included. With greater understanding of the fundamentals, fellow scientists will be able to better interpret the literature, identify knowledge gaps or problems and ultimately invent new production and purification pathways to increase the global availability of medical isotopes.

Copper radionuclides for theranostic applications: towards standardisation of their nuclear data. A mini-review

Copper has several clinically relevant radioisotopes and versatile coordination chemistry, allowing attachment of its radionuclides to biological molecules. This characteristic makes it suitable for applications in molecular imaging or radionuclide targeted therapy. Of particular interest in nuclear medicine today is the theranostic approach. This brief review considers five radionuclides of copper. These are Cu-60, Cu-61, Cu-62, Cu-64, and Cu-67. The first four are positron emitters for imaging, and the last one Cu-67 is a β--emitting radionuclide suitable for targeted therapy. The emphasis here is on theory-aided evaluation of available experimental data with a view to establishing standardised cross-section database for production of the relevant radionuclide in high purity. Evaluated cross section data of the positron emitters have been already extensively reported; so here they are only briefly reviewed. More attention is given to the data of the 68Zn(p,2p)67Cu intermediate energy reaction which is rather commonly used for production of 67Cu.

A digital twin for 64Cu production with cyclotron and solid target system

One method for finding reliable and cost-effective solutions for designing radioisotope production systems is represented by the “digital twin” philosophy of design. Looking at cyclotron solid targets, uncertainties of the particle beam, material composition and geometry play a crucial role in determining the results. The difference between what has been designed and what can be effectively manufactured, where processes such as electroplating are poorly controllable and generate large non-uniformities in deposition, must also be considered. A digital twin, where the target geometry is 3D scanned from real models, can represent a good compromise for connecting “ideal” and “real” worlds. Looking at the 64Ni(p,n)64Cu reaction, different Unstructured-Mesh MCNP6 models have been built starting from the 3D solid target system designed and put into operation by COMECER. A characterization has been performed considering the designed ideal target and a 3D scan of a real manufactured target measured with a ZEISS contact probe. Libraries and physics models have been also tested due to limited cross-section data. Proton spectra in the target volume, 3D proton-neutron-photon flux maps, average energies, power to be dissipated, shut-down dose-rate, 64Cu yield compared with various sources of experimental data and beam axial shifting impact, have been estimated. A digital twin of the 64Ni(p,n)64Cu production device has been characterized, considering the real measured target geometry, paving the way for a fully integrated model suitable also for thermal, structural or fluid-dynamic analyses.

Nuclear data for light charged particle induced production of emerging medical radionuclides

Whatever the radionuclide to be used in nuclear medicine, it is essential to know the expected yield during the production process, but also of all the possible radionuclidic impurities coproduced, that can have an impact on the product final quality, as well as in the related waste management. The availability of the majority of emerging radioisotopes, including the theranostic ones or pairs, is mainly limited by the fact that, for most of them, the optimal production route still needs to be strengthened if not defined in some cases. The aim of this work is to present a review on the charged particle induced nuclear cross sections to produce some emerging radionuclides for medical applications to show that all types of projectiles should be considered in the quest of producing medical radionuclides. An accurate analysis of the production routes is presented for some radionuclides (67Cu, 47Sc, 89Zr, 103Pd, 186gRe, 97Ru, 211At) chosen as examples to highlight (i) how the quality of the final product strongly depends on the chosen target/projectile/energy parameters set, (ii) how deuteron production routes may sometimes be more effective than the proton ones or lead to a different impurity profile and (iii) how α-particle beams may allow to bypass the limitations occurring when using Z = 1 beams. An overview of possible advantages and drawbacks of the cited production routes and of potential cross sections that still need to be measured, is also reported.

The role of chemistry in accelerator-based production and separation of radionuclides as basis for radiolabelled compounds for medical applications

Radiochemical separations used in large scale routine production of diagnostic and therapeutic radionuclides at a particle accelerator for patient care are briefly outlined. The role of chemistry at various stages of development of a production route of a novel radionuclide, namely nuclear data measurement, high-current targetry, chemical processing and quality control of the product, is discussed in detail. Special attention is paid to production of non-standard positron emitters (e.g. 44gSc, 64Cu, 68Ga, etc.) at a cyclotron and novel therapeutic radionuclides (e.g. 67Cu, 225Ac, etc.) at an accelerator. Some typical examples of radiochemical methods involved are presented.

An overview of nuclear data standardisation work for accelerator-based production of medical radionuclides in Pakistan

The standardisation of nuclear reaction cross section data is an integral part of optimisation of production routes of medical radionuclides. The production cross sections are available for the reactor and cyclotron produced radionuclides to be used for diagnostics or therapeutic procedures. The types of nuclear data needed, and the sources of their availability are summarized. The method of standardisation of charged-particle data is briefly described. A historical overview of research work in Pakistan in this direction is given. Examples of a few medically important radionuclides, such as 64Cu, 86Y, 89Zr, 103Pd, 186Re, etc., whose data were standardised and evaluated are highlighted. Calculated thick target yields from the recommended data are given. Some new directions in the nuclear data research are outlined.

Electrochemical deposition of nickel targets from aqueous electrolytes for medical radioisotope production in accelerators: a review

This paper reviews reported methods of the electrochemical deposition of nickel layers which are used as target materials for accelerator production of medical radioisotopes. The review focuses on the electrodeposition carried out from aqueous electrolytes. It describes the main challenges related to the preparation of suitable Ni target layers, such as work with limited amounts of expensive isotopically enriched nickel; electrodeposition of sufficiently thick, smooth and free of cracks layers; and recovery of unreacted Ni isotopes from the irradiated targets and from used electrolytic baths.

Expanding PET-applications in life sciences with positron-emitters beyond fluorine-18

Positron-emission-tomography (PET) has become an indispensable diagnostic tool in modern nuclear medicine. Its outstanding molecular imaging features allow repetitive studies on one individual and with high sensitivity, though no interference. Rather few positron-emitters with near favourable physical properties, i.e. carbon-11 and fluorine-18, furnished most studies in the beginning, preferably if covalently bound as isotopic label of small molecules. With the advancement of PET-devices the scope of in vivo research in life sciences and especially that of medical applications expanded, and other than "standard" PET-nuclides received increasing significance, like the radiometals copper-64 and gallium-68. Especially during the last decades, positron-emitters of other chemical elements have gotten into the focus of interest, concomitant with the technical advancements in imaging and radionuclide production. With known nuclear imaging properties and main production methods of emerging positron-emitters their usefulness for medical application is promising and even proven for several ones already. Unfortunate decay properties could be corrected for, and β+-emitters, especially with a longer half-life, provided new possibilities for application where slower processes are of importance. Further on, (bio)chemical features of positron-emitters of other elements, among there many metals, not only expanded the field of classical clinical investigations, but also opened up new fields of application. Appropriately labelled peptides, proteins and nanoparticles lend itself as newer probes for PET-imaging, e.g. in theragnostic or PET/MR hybrid imaging. Furthermore, the potential of non-destructive in-vivo imaging with positron-emission-tomography directs the view on further areas of life sciences. Thus, exploiting the excellent methodology for basic research on molecular biochemical functions and processes is increasingly encouraged as well in areas outside of health, such as plant and environmental sciences.

Copper-64 based radiopharmaceuticals for brain tumors and hypoxia imaging

INTRODUCTION

The most common and aggressive primary malignancy of the central nervous system is Glioblastoma that, as a wide range of malignant solid tumor, is characterized by extensive hypoxic regions. A great number of PET radiopharmaceuticals have been developed for the identification of hypoxia in solid tumors, among these, we find copper-based tracers. The aim of the current review paper was to provide an overview of radiocopper compounds applied for preclinical and clinical research in brain tumors and hypoxia imaging or therapy.

EVIDENCE ACQUISITION

Copper offers a wide variety of isotopes, useful for nuclear medicine applications, but only ⁶⁴Cu and ⁶⁷Cu are under the spotlight of the scientific community since being good candidates for theranostic applications. Between the two, ⁶⁴Cu availability and production cost have attracted more interest of the scientific community.

EVIDENCE SYNTHESIS

In order to better understand the application of copper-bis thiosemicarbazones in hypoxia imaging, an overview of the role of hypoxia in cancer, existing non-imaging and imaging techniques for hypoxia identification and promising future avenues regarding hypoxia is necessary. Different proposed uptake mechanisms of [⁶⁴Cu][Cu(ATSM)] inside the cell will be discussed and other ⁶⁴Cu-based tracers for brain tumors described.

CONCLUSIONS

Among radio copper compounds [⁶⁴Cu][Cu(ATSM)] is the most studied radiopharmaceutical for imaging and treatment of brain tumors. Experimental evidence suggested that [⁶⁴Cu][Cu(ATSM)] could be more appropriately considered as a marker of over-reduced intracellular state rather than a pure hypoxia agent. Moreover, preliminary clinical data suggested that [⁶⁴Cu]CuCl<inf>2</inf> can be a potentially useful diagnostic agent for malignancies of the central nervous system (CNS).

An investigation of the effects of level density models and alpha optical model potentials on the cross-section calculations for the production of the radionuclides 62Cu, 67Ga, 86Y and 89Zr via some alpha induced reactions

Theoretical studies via nuclear reaction models have an undeniable importance and impact in terms of better understanding of reaction processes and their nature. In this study, by considering the importance of these models and the medical radionuclides, the effects of six level density models and eight alpha optical model potentials on the cross-section calculations for the production of the radionuclides 62Cu, 67Ga, 86Y and 89Zr via 59Co(α,n)62Cu, 60Ni(α,np)62Cu, 65Cu(α,2n)67Ga, 64Zn(α,p)67Ga, 85Rb(α,3n)86Y, 86Sr(α,n)89Zr, 87Sr(α,2n)89Zr and 88Sr(α,3n)89Zr reactions were investigated. Calculations for each reaction route were performed by using the TALYS v1.9 code. The most consistent model with the literature data taken from the Experimental Nuclear Reaction Database (EXFOR), was identified by using the reduced chi-squared statistics in addition to an eyeball estimation. Also, the effects of combinational use of selected models and potentials were investigated by comparing the calculational results with the experimental data.

Development of novel radionuclides for medical applications

Medical radionuclide production technology is well established. There is, however, a constant need for further development of radionuclides. The present efforts are mainly devoted to nonstandard positron emitters (eg, ⁶⁴ Cu, ⁸⁶ Y, ¹²⁴ I, and ⁷³ Se) and novel therapeutic radionuclides emitting low-range β^- particles (eg, ⁶⁷ Cu and ¹⁸⁶ Re), conversion or Auger electrons (eg, ^117m Sn and ⁷⁷ Br), and α particles (eg, ²²⁵ Ac). A brief account of various aspects of development work (ie, nuclear data, targetry, chemical processing, and quality control) is given. For each radionuclide under consideration, the status of technology for clinical scale production is discussed. The increasing need of intermediate-energy multiple-particle accelerating cyclotrons is pointed out.

Nuclear data for production and medical application of radionuclides: Present status and future needs

INTRODUCTION

The significance of nuclear data in the choice and medical application of a radionuclide is considered: the decay data determine its suitability for organ imaging or internal therapy and the reaction cross section data allow optimisation of its production route. A brief discussion of reaction cross sections and yields is given.

STANDARD RADIONUCLIDES

The standard SPECT, PET and therapeutic radionuclides are enumerated and their decay and production data are considered. The status of nuclear data is generally good. Some existing discrepancies are outlined. A few promising alternative production routes of ^99mTc and ⁶⁸Ga are discussed.

RESEARCH-ORIENTED RADIONUCLIDES

The increasing significance of non-standard positron emitters in organ imaging and of low-energy highly-ionizing radiation emitters in internal therapy is discussed, their nuclear data are considered and a brief review of their status is presented. Some other related nuclear data issues are also mentioned.

PRODUCTION OF RADIONUCLIDES USING NEWER TECHNOLOGIES

The data needs arising from new directions in radionuclide applications (multimode imaging, theranostic approach, radionanoparticles, etc.) are considered. The future needs of data associated with possible utilization of newer irradiation technologies (intermediate energy cyclotron, high-intensity photon accelerator, spallation neutron source, etc.) are outlined.

CONCLUSION

Except for a few small discrepancies, the available nuclear data are sufficient for routine production and application of radionuclides. Considerable data needs exist for developing novel radionuclides for applications. The developing future technologies for radionuclide production will demand further data-related activities.

Is there an interest to use deuteron beams to produce non-conventional radionuclides?

With the recent interest on the theranostic approach, there has been a renewed interest for alternative radionuclides in nuclear medicine. They can be produced using common production routes, i.e., using protons accelerated by biomedical cyclotrons or neutrons produced in research reactors. However, in some cases, it can be more valuable to use deuterons as projectiles. In the case of Cu-64, smaller quantities of the expensive target material, Ni-64, are used with deuterons as compared with protons for the same produced activity. For the Sc-44m/Sc-44g generator, deuterons afford a higher Sc-44m production yield than with protons. Finally, in the case of Re-186g, deuterons lead to a production yield five times higher than protons. These three examples show that it is of interest to consider not only protons or neutrons but also deuterons to produce alternative radionuclides.

The present and future of medical radionuclide production

Medical radionuclide production technology is well established. Both reactors and cyclotrons are utilized for production; the positron emitters, however, are produced exclusively using cyclotrons. A brief survey of the production methods of most commonly used diagnostic and therapeutic radionuclides is given. The emerging radionuclides are considered in more detail. They comprise novel positron emitters and therapeutic radionuclides emitting low-range electrons and α-particles. The possible alternative production routes of a few established radionuclides, like 68Ga and 99mTc, are discussed. The status of standardisation of production data of the commonly used as well as of some emerging radionuclides is briefly mentioned. Some notions on anticipated future trends in the production and application of radionuclides are considered.

New trends in nuclear data research for medical radionuclide production

Nuclear reaction cross section data are of great significance in optimisation of production routes of radionuclides. This article deals with some newer aspects of data research related to production of both standard and novel radionuclides. The recent work to standardise the known data is discussed and new measurements with regard to further optimisation of production routes of some commonly used radionuclides are mentioned. Attempts to increase the specific activity of some reactor-produced radionuclides through the use of charged-particle induced reactions are outlined. The jeopardy in the supply of99mTcviaa fission-produced99Mo/99mTc generator is considered and its possible direct production at a cyclotron is briefly discussed. Regarding the novel radionuclides, development work is presently focussed on non-standard positron emitters for diagnosis and on low-range highly ionising radiation emitters for internal radiotherapy. Recent nuclear reaction cross section measurements related to the production of the two types of radionuclides are briefly reviewed and some anticipated trends in nuclear data research are considered.

Development of novel positron emitters for medical applications: nuclear and radiochemical aspects

In molecular imaging, the importance of novel longer lived positron emitters, also termed as non-standard or innovative PET radionuclides, has been constantly increasing, especially because they allow studies on slow metabolic processes and in some cases furnish the possibility of quantification of radiation dose in internal radiotherapy. Considerable efforts have been invested worldwide and about 25 positron emitters have been developed. Those efforts relate to interdisciplinary studies dealing with basic nuclear data, high current charged particle irradiation, efficient radiochemical separation and quality control of the desired radionuclide, and recovery of the enriched target material for reuse. In this review all those aspects are briefly discussed, with particular reference to three radionuclides, namely 64Cu, 124I and 86Y, which are presently in great demand. For each radionuclide several nuclear routes were investigated but the ( p,n) reaction on an enriched target isotope was found to be the best for use at a small-sized cyclotron. Some other positron emitting radionuclides, such as 55Co, 76Br, 89Zr, 82mRb, 94mTc, 120I, etc., were also produced via the low-energy (p,n), (p,α) or (d,n) reaction. On the other hand, the production of radionuclides 52Fe, 73Se, 83Sr, etc. using intermediate energy (p,xn) or (d,xn) reactions needs special consideration, the nuclear data and chemical processing methods being of key importance. In a few special cases, a high intensity 3He- or α-particle beam could be an added advantage. The production of some potentially interesting positron emitters via generator systems, for example 44Ti/44Sc, 72Se/72As and 140N d/140Pr is considered. The significance of new generation high power accelerators is briefly discussed.

Evaluation of excitation functions of proton, ³He- and α-particle induced reactions for production of the medically interesting positron-emitter bromine-76

Cross section data for production of the medically interesting radionuclide ⁷⁶Br (T(½)=16.2 h) via the proton induced reactions on ⁷⁶Se, ⁷⁷Se, ⁷⁸Se and ⁷⁹Br, and ³He- and α-particle induced reactions on ⁷⁵As were evaluated. The nuclear model codes STAPRE, EMPIRE and TALYS were used to check the consistency in the experimental data and a statistical procedure was applied to derive the recommended excitation functions. A comparison of various production routes of ⁷⁶Br (and of ⁷⁵Br) is presented.

Highly stable acyclic bifunctional chelator for 64Cu PET imaging

Ligand L1, based on a pyridine scaffold, functionalized by two bis(methane phosphonate)aminomethyl groups, was shown to display a very high affinity towards Cu(II) (log K CuL=22.7) and selectivity over Ni(II), Co(II), Zn(II) and Ga(III) (Δ log K ML>4) as shown by the values of the stability constants obtained from potentiometric measurements. Insights into the coordination mode of the ligand around Cu(II) cation were obtained by UV-Vis absorption and EPR spectroscopies as well as density functional theory (DFT) calculations (B3LYP model) performed in aqueous solution. The results point to a pentacoordination pattern of the metal ion in the fully deprotonated [CuL1]6− species. Considering the beneficial thermodynamic parameters of this ligand, kinetic experiments were run to follow the formation of the copper(II) complexes, indicating a very rapid formation of the complex, appropriat e for 64Cu complexation. As L1 represents a particularly interesting target within the frame of 64Cu PET imaging, a synthetic protocol was developed to introduce a labeling function on the pyridyl moiety of L1, thereby affording L2, a potential bifunctional chelator (BFC) for PET imaging.

Evaluation of excitation functions of proton and deuteron induced reactions on enriched tellurium isotopes with special relevance to the production of iodine-124

Cross-section data for the production of medically important radionuclide (124)I via five proton and deuteron induced reactions on enriched tellurium isotopes were evaluated. The nuclear model codes, STAPRE, EMPIRE and TALYS, were used for consistency checks of the experimental data. Recommended excitation functions were derived using a well-defined statistical procedure. Therefrom integral yields were calculated. The various production routes of (124)I were compared. Presently the (124)Te(p,n)(124)I reaction is the method of choice; however, the (125)Te(p,2n)(124)I reaction also appears to have great potential.