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

Scandium Radioisotopes-Toward New Targets and Imaging Modalities

The concept of theranostics uses radioisotopes of the same or chemically similar elements to label biological ligands in a way that allows the use of diagnostic and therapeutic radiation for a combined diagnosis and treatment regimen. For scandium, radioisotopes -43 and -44 can be used as diagnostic markers, while radioisotope scandium-47 can be used in the same configuration for targeted therapy. This work presents the latest achievements in the production and processing of radioisotopes and briefly characterizes solutions aimed at increasing the availability of these radioisotopes for research and clinical practice.

Membrane-based microfluidic solvent extraction of Ga-68 from aqueous Zn solutions: towards an automated cyclotron production loop

BACKGROUND

The radionuclide Ga-68 is commonly used in nuclear medicine, specifically in positron emission tomography (PET). Recently, the interest in producing Ga-68 by cyclotron irradiation of [⁶⁸Zn]Zn nitrate liquid targets is increasing. However, current purification methods of Ga-68 from the target solution consist of multi-step procedures, thus, leading to a significant loss of activity through natural decay. Additionally, several processing steps are needed to recycle the costly, enriched target material.

RESULTS

To eventually allow switching from batch to continuous production, conventional batch extraction and membrane-based microfluidic extraction were compared. In both approaches, Ga-68 was extracted using N-benzoyl-N-phenylhydroxylamine in chloroform as the organic extracting phase. Extraction efficiencies of up to 99.5% ± 0.6% were achieved within 10 min, using the batch approach. Back-extraction of Ga-68 into 2 M HCl was accomplished within 1 min with efficiencies of up to 94.5% ± 0.6%. Membrane-based microfluidic extraction achieved 99.2% ± 0.3% extraction efficiency and 95.8% ± 0.8% back-extraction efficiency into 6 M HCl. When executed on a solution irradiated with a 13 MeV cyclotron at TRIUMF, Canada, comparable efficiencies of 97.0% ± 0.4% were achieved. Zn contamination in the back-extracted Ga-68 solution was found to be below 3 ppm.

CONCLUSIONS

Microfluidic solvent extraction is a promising method in the production of Ga-68 achieving high efficiencies in a short amount of time, potentially allowing for direct target recycling.

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.

Engineering a modular 44Ti/44Sc generator: eluate evaluation in preclinical models and estimation of human radiation dosimetry

BACKGROUND

⁴⁴Sc/⁴⁷Sc is an attractive theranostic pair for targeted in vivo positron emission tomographic (PET) imaging and beta-particle treatment of cancer. The ⁴⁴Ti/⁴⁴Sc generator allows daily onsite production of this diagnostic isotope, which may provide an attractive alternative for PET facilities that lack in-house irradiation capabilities. Early animal and patient studies have demonstrated the utility of ⁴⁴Sc. In our current study, we built and evaluated a novel clinical-scale ⁴⁴Ti/⁴⁴Sc generator, explored the pharmacokinetic profiles of ⁴⁴ScCl₃, [⁴⁴Sc]-citrate and [⁴⁴Sc]-NODAGA (1,4,7-triazacyclononane,1-glutaric acid-4,7-acetic acid) in naïve mice, and estimated the radiation burden of ⁴⁴ScCl₃ in humans.

METHODS

⁴⁴Ti/⁴⁴Sc (101.2 MBq) in 6 M HCl solution was utilized to assemble a modular ZR resin containing generator. After assembly, ⁴⁴Sc was eluted with 0.05 M HCl for further PET imaging and biodistribution studies in female Swiss Webster mice. Based on the biodistribution data, absorbed doses of ^44/47ScCl₃ in human adults were calculated for 18 organs and tissues using the IDAC-Dose software.

RESULTS

⁴⁴Ti in 6 M HCl was loaded onto the organic resin generator with a yield of 99.97%. After loading and initial stabilization, ⁴⁴ScCl₃ was eluted with 0.05 M HCl in typical yields of 82.9 ± 5.3% (N = 16), which was normalized to the estimated generator capacity. Estimated generator capacity was computed based on elution time interval and the total amount of ⁴⁴Ti loaded on the generator. Run in forward and reverse directions, the ⁴⁴Sc/⁴⁴Ti ratio from a primary column was significantly improved from 1038 ± 440 to 3557 ± 680 (Bq/Bq) when a secondary, replaceable, ZR resin cartridge was employed at the flow outlet. In vivo imaging and ex vivo distribution studies of the reversible modular generator for ⁴⁴ScCl₃, [⁴⁴Sc]-citrate and [⁴⁴Sc]-NODAGA show that free ⁴⁴Sc remained in the circulation significantly longer than the chelated ⁴⁴Sc. The dose estimation of ⁴⁴ScCl₃ reveals that the radiation burden is 0.146 mSv/MBq for a 70 kg adult male and 0.179 mSv/MBq for a 57 kg adult female. Liver, spleen and heart wall will receive the highest absorbed dose: 0.524, 0.502, and 0.303 mGy/MBq, respectively, for the adult male.

CONCLUSIONS

A clinical-scale ⁴⁴Ti/⁴⁴Sc generator system with a modular design was developed to supply ⁴⁴ScCl₃ in 0.05 M HCl, which is suitable for further radiolabeling and in vivo use. Our data demonstrated that free ⁴⁴ScCl₃ remained in the circulation for extended periods, which resulted in approximately 10 times greater radiation burden than stably chelated ⁴⁴Sc. Stable ⁴⁴Sc/⁴⁷Sc-complexation will be more favorable for in vivo use and for clinical utility.

Diagnosis of Glioblastoma by Immuno-Positron Emission Tomography

Simple Summary

Neuroimaging has transformed the way brain tumors are diagnosed and treated. Although different non-invasive modalities provide very helpful information, in some situations, they present a limited value. By merging the specificity of antibodies with the resolution, sensitivity, and quantitative capabilities of positron emission tomography (PET), “Immuno-PET” allows us to conduct the non-invasive diagnosis and monitoring of patients over time using antibody-based probes as an in vivo, integrated, quantifiable, 3D, full-body “immunohistochemistry”, like a “virtual biopsy”. This review provides and focuses on immuno-PET applications and future perspectives of this promising imaging approach for glioblastoma.

Abstract

Neuroimaging has transformed neuro-oncology and the way that glioblastoma is diagnosed and treated. Magnetic Resonance Imaging (MRI) is the most widely used non-invasive technique in the primary diagnosis of glioblastoma. Although MRI provides very powerful anatomical information, it has proven to be of limited value for diagnosing glioblastomas in some situations. The final diagnosis requires a brain biopsy that may not depict the high intratumoral heterogeneity present in this tumor type. The revolution in “cancer-omics” is transforming the molecular classification of gliomas. However, many of the clinically relevant alterations revealed by these studies have not yet been integrated into the clinical management of patients, in part due to the lack of non-invasive biomarker-based imaging tools. An innovative option for biomarker identification in vivo is termed “immunotargeted imaging”. By merging the high target specificity of antibodies with the high spatial resolution, sensitivity, and quantitative capabilities of positron emission tomography (PET), “Immuno-PET” allows us to conduct the non-invasive diagnosis and monitoring of patients over time using antibody-based probes as an in vivo, integrated, quantifiable, 3D, full-body “immunohistochemistry” in patients. This review provides the state of the art of immuno-PET applications and future perspectives on this imaging approach for glioblastoma.

Improved separation scheme for 44Sc produced by irradiation of natCa targets with 12.8 MeV protons

INTRODUCTION

⁴⁴Sc is of great interest as a positron emission tomography (PET) radionuclide due to its suitable nuclear characteristics: E_β⁺max = 1.47 MeV, branching ratio 94.3% and convenient half-life of 3.97 h. Here, ⁴⁴Sc was produced via the widely used reaction ⁴⁴Ca (p,n)⁴⁴Sc using natural calcium as a target.

METHODS

The irradiation was performed at TRIUMF using the 13 MeV cyclotron. The separation consisted of a combination of DGA branched resin and Dowex 50Wx8 (200-400 mesh). The distribution coefficients of Sc³⁺ on Dowex 50Wx8 (NH₄⁺ form, 200-400 mesh) with ammonium α-hydroxyisobutyrate (pH = 4.8) medium were determined in this study.

RESULTS AND CONCLUSION

The tested scheme allows both a reliable separation of ⁴⁴Sc from the target material as well as from the other competitive metals and a final fraction with high specific activity. The achieved radiochemical yield was 95 ± 3%.