A simple thick target for production of 89Zr using an 11MeV cyclotron

Functional Diversity in Radiolabeled Nanoceramics and Related Biomaterials for the Multimodal Imaging of Tumors

Nanotechnology advances have the potential to assist toward the earlier detection of diseases, giving increased accuracy for diagnosis and helping to personalize treatments, especially in the case of noncommunicative diseases (NCDs) such as cancer. The main advantage of nanoparticles, the scaffolds underpinning nanomedicine, is their potential to present multifunctionality: synthetic nanoplatforms for nanomedicines can be tailored to support a range of biomedical imaging modalities of relevance for clinical practice, such as, for example, optical imaging, computed tomography (CT), magnetic resonance imaging (MRI), single photon emission computed tomography (SPECT), and positron emission tomography (PET). A single nanoparticle has the potential to incorporate myriads of contrast agent units or imaging tracers, encapsulate, and/or be conjugated to different combinations of imaging tags, thus providing the means for multimodality diagnostic methods. These arrangements have been shown to provide significant improvements to the signal-to-noise ratios that may be obtained by molecular imaging techniques, for example, in PET diagnostic imaging with nanomaterials versus the cases when molecular species are involved as radiotracers. We surveyed some of the main discoveries in the simultaneous incorporation of nanoparticulate materials and imaging agents within highly kinetically stable radio-nanomaterials as potential tracers with (pre)clinical potential. Diversity in function and new developments toward synthesis, radiolabeling, and microscopy investigations are explored, and preclinical applications in molecular imaging are highlighted. The emphasis is on the biocompatible materials at the forefront of the main preclinical developments, e.g., nanoceramics and liposome-based constructs, which have driven the evolution of diagnostic radio-nanomedicines over the past decade.

Anion exchange and extraction chromatography tandem column isolation of zirconium-89 (89Zr) from cyclotron bombarded targets using an automated fluidic platform

The long-lived positron emitter ⁸⁹Zr is a highly promising nuclide employed in diagnostic Positron Emission Tomography (PET) imaging. Methods of radiochemical processing to obtain ⁸⁹Zr for clinical use are traditionally performed with a single hydroxamate resin column. Herein, we present a tandem column purification method for the preparation of high-purity ⁸⁹Zr from cyclotron bombarded natural Y metal foils. The primary column is a macroporous, strongly basic anion exchange resin on styrene divinylbenzene co-polymer. The secondary microcolumn, with an internal volume of 33 μL, is packed with an extraction chromatography resin (ExCR) loaded with di-(2-ethylhexyl)phosphoric acid (HDEHP). A condition of "inverted selectivity" is presented, wherein the ⁸⁹Zr elution from the primary column is synonymous with the load condition on the secondary column. The ability to transfer ⁸⁹Zr from one column to the next allows two sequential purification steps to be performed prior to the final elution of the ⁸⁹Zr product. This approach assures delivery of high purity ⁸⁹Zr. The tandem column purification process has been implemented into a prototype automated fluidic system. Optimization of the method is presented, followed by evaluation of the process using seven cyclotron bombarded Y metal foil targets. Once optimized, we found that 93.7 ± 2.3% of the ⁸⁹Zr present in the foils was recovered in the secondary column elution fraction (0.8 M oxalic acid). Radiochromatograms of the product elution peaks enabled determination of full width at half-maximum (FWHM) and ⁸⁹Zr collection yields as a function of volume. Because of the small size of the secondary microcolumn, a ⁸⁹Zr product volume of ∼0.28 mL is reported, which provides a substantially increased nuclide concentration over traditional methods. Finally, we evaluated the transchelation of the resulting ⁸⁹Zr oxalate product to deferoxamine mesylate (DFOM) salt. We observed effective specific activities (ESA) and bindable metals concentrations ([M_B]) that exceed those reported by the traditional single hydroxamate column method.

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.

Target manufacturing by Spark Plasma Sintering for efficient 89Zr production

Zirconium-89 (⁸⁹Zr) is an emerging radionuclide for positron emission tomography (PET), with nuclear properties suitable for imaging slow biological processes in cellular targets. The ⁸⁹Y(p,n)⁸⁹Zr nuclear reaction is commonly exploited as the main production route with medical cyclotrons accelerating low-energy (< 20 MeV) and low-current (< 100 μA) proton beams. Usually, natural yttrium solid targets manufactured by different methods, including yttrium electrodeposition, yttrium sputtering, compressed yttrium powders, and foils, were employed. In this study, the Spark Plasma Sintering (SPS) technique has been investigated, for the first time, to manufacture yttrium solid targets for an efficient ⁸⁹Zr radionuclide yield. The natural yttrium disc was bonded to a niobium backing plate using a commercial SPS apparatus and a prototype machine assembled at the University of Pavia. The resulting targets were irradiated in a TR19 cyclotron with a 12 MeV proton beam at 50 μA. A dedicated dissolution module, obtained from a commercial system, was used to develop an automated process for the purification and recovery of the produced ⁸⁹Zr radionuclide. The production yield and recovery efficiency were measured and compared to ⁸⁹Zr produced by irradiating standard yttrium foils. SPS manufactured targets withstand an average heat power density of approximately 650 W∙cm^-2 for continuous irradiation up to 5 h without visible damage. A saturation yield of 14.12 ± 0.38 MBq/μAh was measured. The results showed that the obtained ⁸⁹Zr production yield and quality were comparable to similar data obtained using standard yttrium foil targets. In conclusion, the present work demonstrates that the SPS technique might be a suitable technical manufacturing solution aimed at high-yield ⁸⁹Zr radioisotope production.

Evaluation of nuclear reaction cross sections for optimization of production of the important non-standard positron emitting radionuclide 89Zr using proton and deuteron induced reactions on 89Y target

⁸⁹Zr (T_1/2 = 3.27 d) is an important β⁺-emitting radionuclide of zirconium used in immuno PET. The excitation functions of the ⁸⁹Y(d,2n)⁸⁹Zr and ⁸⁹Y(p,n)⁸⁹Zr reactions were analyzed to deduce the optimum conditions for the high purity production of ⁸⁹Zr. The nuclear model codes ALICE-IPPE, EMPIRE 3.2 and TALYS 1.9 were used to check the consistency and reliability of the experimental data. A polynomial fit to the chosen data for each reaction gave the excitation function, which was then used for the integral yield calculation of the product. The amount of the major radioactive impurity ⁸⁸Zr was precisely analyzed for both the proton and the deuteron induced reactions on the ⁸⁹Y target.

FLUKA simulation yields in a comparison with theoretical and experimental yields relevant to 89Zr produced in the 89Y(p,n) reaction

The high importance of zirconium-89 (T1/2 = 78.41 h) is related to its applications in medical imaging. It can be produced at low-energy cyclotrons by the reaction 89Y(p,n)89Zr. There exist several publications on its production at low and intermediate energies but there is discrepancy with simulated data. In this study we considered the experimental parameters for four different types of yttrium foil targets reported in literature. The experimental parameters considered were the target geometry, beam profile, and angle of the target relative to the beam during irradiation. The Monte-Carlo code FLUKA was used to calculate production yields. The resulting values obtained by FLUKA from pencil beam or spread energy beam were compared to the theoretical yields obtained from the excitation function and the experimental ones. The FLUKA prediction for 89Z-yield reached ≈50 MBq/μA · h which agrees to a high extent with experimental and theoretical yields reported for the different targets.

Preparation of Zirconium-89 Solutions for Radiopharmaceutical Purposes: Interrelation Between Formulation, Radiochemical Purity, Stability and Biodistribution

Zirconium-89 is a promising radionuclide for nuclear medicine. The aim of the present work was to find a suitable method for obtaining zirconium-89 solutions for radiopharmaceutical purposes. For this purpose, the ion exchange behavior of zirconium-89 solutions was studied. Radio-TLC (thin layer chromatography) and biodistribution studies were carried out to understand speciation of zirconium-89 complexes and their role in the development of new radiopharmaceuticals. Three methods of zirconium-89 isolation were studied using ZR (hydroxamate) and Chelex-100 resins. It was found that ZR-resin alone is not enough to obtain stable zirconium-89 formulations. An easy and effective method of reconstitution of [⁸⁹Zr]Zr-oxalate to [⁸⁹Zr]Zr-citrate using Chelex-100 resin was developed. Developed procedures allow obtaining [⁸⁹Zr]Zr-oxalate (in 0.1 M sodium oxalate solution) and [⁸⁹Zr]Zr-citrate (in 0.1–1.0 M sodium citrate solution). These solutions are perfectly suitable and convenient for radiopharmaceutical purposes. Our results prove [⁸⁹Zr]Zr-citrate to be advantageous over [⁸⁹Zr]Zr-oxalate. During evaluation of speciation of zirconium-89 complexes, a new TLC method was developed, since it was proved that there is no comprehensive method for analysis or zirconium-89 preparations. The new method provides valuable insights about the content of “active” ionic form of zirconium-89. The interrelation of the chromatographic behavior of zirconium-89 preparations and their biodistribution was studied.

Production cross sections of Mo, Nb and Zr radioisotopes from α-induced reaction on natZr

Cross sections of α-induced reactions on natural zirconium were measured up to 50 MeV using the stacked-foil technique, activation method and high resolution γ-ray spectrometry. The production cross sections of ^93m,99Mo, ^{90g,92m,95g,95m,96}Nb and ^88,89g,95Zr were determined and compared with other experimental data measured earlier and result of theoretical calculations. The integral thick target yield of ⁹⁹Mo was deduced from the measured cross section data.

Radioactive Transition Metals for Imaging and Therapy

Nuclear medicine is composed of two complementary areas, imaging and therapy. Positron emission tomography (PET) and single-photon imaging, including single-photon emission computed tomography (SPECT), comprise the imaging component of nuclear medicine. These areas are distinct in that they exploit different nuclear decay processes and also different imaging technologies. In PET, images are created from the 511 keV photons produced when the positron emitted by a radionuclide encounters an electron and is annihilated. In contrast, in single-photon imaging, images are created from the γ rays (and occasionally X-rays) directly emitted by the nucleus. Therapeutic nuclear medicine uses particulate radiation such as Auger or conversion electrons or β^- or α particles. All three of these technologies are linked by the requirement that the radionuclide must be attached to a suitable vector that can deliver it to its target. It is imperative that the radionuclide remain attached to the vector before it is delivered to its target as well as after it reaches its target or else the resulting image (or therapeutic outcome) will not reflect the biological process of interest. Radiochemistry is at the core of this process, and radiometals offer radiopharmaceutical chemists a tremendous range of options with which to accomplish these goals. They also offer a wide range of options in terms of radionuclide half-lives and emission properties, providing the ability to carefully match the decay properties with the desired outcome. This Review provides an overview of some of the ways this can be accomplished as well as several historical examples of some of the limitations of earlier metalloradiopharmaceuticals and the ways that new technologies, primarily related to radionuclide production, have provided solutions to these problems.

Tandem column isolation of zirconium-89 from cyclotron bombarded yttrium targets using an automated fluidic platform: Anion exchange to hydroxamate resin columns

The development of a tandem column purification method for the preparation of high-purity ⁸⁹Zr(IV) oxalate is presented. The primary column was a macroporous strongly basic anion exchange resin on styrene divinylbenzene co-polymer. The secondary column, with an internal volume of 33 μL, was packed with hydroxamate resin. A condition of inverted selectivity was developed, whereby the ⁸⁹Zr eluent solution for the primary column is equivalent to the ⁸⁹Zr load solution for the secondary column. The ability to transfer ⁸⁹Zr from one column to the next allows two sequential column clean-up methods to be performed prior to the final elution of the ⁸⁹Zr(IV) oxalate. This approach assures delivery of high purity ⁸⁹Zr product and assures a ⁸⁹Zr product that is eluted in a substantially smaller volume than is possible when using the traditionally-employed single hydroxamate resin column method. The tandem column purification process has been implemented into a prototype automated fluidic system. The system is configured with on-line gamma detection so column effluents can be monitored in near-real time. The automated method was tested using seven cyclotron bombarded Y foil targets. It was found that 95.1 ± 1.3% of the ⁸⁹Zr present in the foils was recovered in the secondary column elution fraction. Furthermore, elution peak analysis of several ⁸⁹Zr elution profile radiochromatograms made possible the determination of ⁸⁹Zr recovery as a function of volume; a ⁸⁹Zr product volume that contains 90% of the mean secondary column elution peak can be obtained in 0.29 ± 0.06 mL (representing 86 ± 5% of the ⁸⁹Zr activity in the target). This product volume represents a significant improvement in radionuclide product concentration over the predominant method used in the field. In addition to the reduced ⁸⁹Zr product elution volume, titrations of the ⁸⁹Zr product with deferoxamine mesylate salt across two preparatory methods resulted in mean effective specific activity (ESA) values of 279 and 340 T Bq·mmole^-1 and mean bindable metals concentrations ([M_B]) of 13.5 and 16.7 nmole·g^-1. These ESA and [M_B] values infer that the ⁸⁹Zr(IV) oxalate product resulting from this tandem column isolation method has the highest purity reported to date.