Radiolysis reduction in liquid solution targets for the production of 89Zr

Transition and Post-Transition Radiometals for PET Imaging and Radiotherapy

Radiometals are an exciting class of radionuclides because of the large number of metallic elements available that have medically useful isotopes. To properly harness radiometals, they must be securely bound by chelators, which must be carefully matched to the radiometal ion to maximize radiolabeling performance and the stability of the resulting complex. This chapter focuses on practical aspects of radiometallation chemistry including chelator selection, radiolabeling procedures and conditions, radiolysis prevention, purification, quality control, requisite equipment and reagents, and useful tips.

Production of Co-58m in a siphon-style liquid target on a medical cyclotron

We present the production of ^58mCo on a small, 13 MeV medical cyclotron utilizing a siphon style liquid target system. Different concentrated iron(III)-nitrate solutions of natural isotopic distribution were irradiated at varying initial pressures and subsequently separated by solid phase extraction chromatography. The radio cobalt (^58m/gCo and ⁵⁶Co) was successfully produced with saturation activities of (0.35 ± 0.03) MBq μA^-1 for ^58mCo with a separation recovery of (75 ± 2) % of cobalt after one separation step utilizing LN-resin.

Cyclotron production of 103Pd using a liquid target

INTRODUCTION

In this work, we present the first feasibility study on the production of the medically important radionuclide ¹⁰³Pd via the ¹⁰³Rh(p,n)¹⁰³Pd reaction by cyclotron irradiation of a liquid target. Using a liquid target removes the time consuming and complex dissolution process of rhodium post-irradiation due to its chemically inactive nature and thereby will improve the accessibility of this radioisotope.

METHODS

Liquid targets made from Rh(NO₃)₃·×H₂O salt dissolved in de-ionized water were irradiated using a 12 MeV beam at the TR13 cyclotron at TRIUMF, Vancouver.

RESULTS

A maximum EOB activity of 1.03 ± 0.05 MBq was achieved with the tested conditions, sufficient for basic radiochemistry studies. An effective separation method using anion exchange chromatography is reported using 1 M HNO₃ as an eluent for rhodium (90.1 ± 2.1 % recovery) and a 1:1 mixture of 0.5 M NH₃ + NH₄Cl palladium eluent (103.8 ± 2.3 % recovery). The solution showed good in-target pressure stability. However, the production efficiency decreased significantly with higher solution concentrations and irradiation lengths which puts into question the scaling potential of this method.

CONCLUSION

This proof-of-concept study has demonstrated the potential for using liquid targets as complementary production method of ¹⁰³Pd for research purposes. The liquid target route faces several scaling challenges but can nonetheless improve the availability of ¹⁰³Pd and consequently aid in widening its utility for radiopharmaceuticals.

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.

Cyclotron Production of PET Radiometals in Liquid Targets: Aspects and Prospects

The present review describes the methodological aspects and prospects of the production of Positron Emission Tomography (PET) radiometals in a liquid target using low-medium energy medical cyclotrons. The main objective of this review is to delineate and discuss the critical factors involved in the liquid target production of radiometals, including type of salt solution, solution composition, beam energy, beam current, the effect of irradiation duration (length of irradiation) and challenges posed by in-target chemistry in relation with irradiation parameters. We also summarize the optimal parameters for the production of various radiometals in liquid targets. Additionally, we discuss the future prospects of PET radiometals production in the liquid targets for academic research and clinical applications. Significant emphasis has been given to the production of ⁶⁸Ga using liquid targets due to the growing demand for ⁶⁸Ga labeled PSMA vectors, [⁶⁸Ga]- Ga-DOTATATE, [⁶⁸Ga]Ga-DOTANOC and some upcoming ⁶⁸Ga labeled radiopharmaceuticals. Other PET radiometals included in the discussion are ⁸⁶Y, ⁶³Zn and ⁸⁹Zr.

PyRad: A software shell for simulating radiolysis with Qball package

The assessment of the radiolytic stability of media is an important task in the fields of nuclear power engineering and radiochemistry. Such studies must be carried out in special laboratory conditions with the use of sources of ionizing radiation, which may increase personal doses of the staff. In addition, difficulties arise in studying the products of irradiated media. While it is impossible to abandon experiments to obtain reliable results in this area, computational methods of quantum chemistry can reduce the number of experiments and help understand the mechanisms of the reactions that occur during radiolysis. Here we would like to present a software shell of the Qb@ll program performing time-dependent density functional theory simulations of the radiolysis process.

Improved Sc-44 production in a siphon-style liquid target on a medical cyclotron

In order to use new and promising radiometals for molecular imaging, it is important that they can be obtained as inexpensively and easily as possible. This often requires a cyclotron with solid target hardware or a radionuclide generator, which are not widely available for rarely used radionuclides. Here, we investigate the improved production of ⁴⁴Sc with a siphon-style liquid target system and compare to our previous work with a simple liquid target. A metal salt solution with a high concentration of natural abundance Ca(NO₃)₂ (0.14 g/cm³) was irradiated with a medical cyclotron (12 MeV protons; 20 μA). ⁴⁴Sc was produced via the ^natCa(p,x)⁴⁴Sc reaction. As the pressure increase during irradiation was reduced in the siphon-style target, it was possible to irradiate with a higher proton beam current (20 μA) than with the simple liquid target system (7.9 μA). In addition, the saturation yield per μA of ⁴⁴Sc was increased by a factor of 3.18 ± 0.05 (6.2 ± 0.1 MBq/μA with the siphon target versus 1.94 ± 0.08 MBq/μA with the simple target). This results in an overall increase in ⁴⁴Sc activity by a factor of 11.