Taking cyclotron 68Ga production to the next level: Expeditious solid target production of 68Ga for preparation of radiotracers

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.

Is Copper-61 the New Gallium-68? Automation and Preclinical Proof-of-Concept of 61Cu-Based Radiopharmaceuticals for Prostate Cancer Imaging

Background: While gallium-68 has traditionally dominated PET imaging in oncology, copper radionuclides have sparked interest for their potential applications in nuclear medicine and theranostics. Considering the advantageous physical decay properties of copper-61 compared to those of gallium-68, we describe a fully automated GMP-compliant synthesis process for 61Cu-based radiopharmaceuticals and demonstrate their in vivo application for targeting the overexpressed PSMA by PET/MR imaging. Methods: Copper-61 was obtained through the irradiation of natural zinc liquid targets in a biomedical cyclotron. [61Cu]Cu-DOTAGA-PSMA-I&T and [61Cu]Cu-NODAGA-PSMA-I&T were produced without manual intervention in two Synthera® Extension modules. Radiochemical purity was analyzed by radio-HPLC and iTLC. Cellular uptake was evaluated in LNCaP and DU145 cells. In vivo PET/MRI was performed in control mice to evaluate the biodistribution of both radiopharmaceuticals, and in tumor-bearing mice to assess the targeting ability towards PSMA. Results: The fully automated process developed proved to be effective for the synthesis of 61Cu-based radiopharmaceuticals, with appropriate molar activities. The final products exhibited high radiochemical purity (>98%) and remained stable for up to 6 h after the EOS. A time-dependent increase in cellular uptake was observed in LNCaP cells, but not in DU145 cells. As opposed to [61Cu]Cu-NODAGA-PSMA-I&T, [61Cu]Cu-DOTAGA-PSMA-I&T exhibited poor kinetic stability in vivo. Subsequent PET/MR imaging with [61Cu]Cu-NODAGA-PSMA-I&T showed tumor uptake lasting up to 4 h post-injection, predominant renal clearance, and no detectable accumulation in non-targeted organs. Conclusions: These results demonstrate the feasibility of the implemented process, which yields adequate amounts of high-quality radiopharmaceuticals and can be adapted to any standard production facility. This streamlined approach enhances reproducibility and scalability, bringing copper-61 closer to widespread clinical use, to the detriment of the conventionally accepted gallium-68.

Performance evaluation of Gallium-68 radiopharmaceuticals production using liquid target PETtrace 800 cyclotron

Due to increased demand, cyclotron has an expanding role in producing Gallium-68 (68Ga) radiopharmaceuticals using solid and liquid targets. Though the liquid target produces lower end-of-bombardment activity compared to the solid target, our study presents the performance of 68Ga radiopharmaceuticals production using the liquid target by evaluating the end-of-bombardment activity and the end-of-purification activity of [68Ga]GaCl3. We also present the effect of increasing irradiation time, which significantly improves the end-of-synthesis yield. From the result obtained, the end-of-bombardment activity produced was 4.48 GBq, and the [68Ga]GaCl3 end-of-purification activity produced was 2.51 GBq with below-limit metallic impurities. Increasing the irradiation time showed a significant increase in the end-of-synthesis activity from 1.33 GBq to 1.95 GBq for [68Ga]Ga-PSMA-11 and from 1.13 GBq to 1.74 GBq for [68Ga]Ga-DOTA-TATE. Based on the improvements made, the liquid target production of 68Ga radiopharmaceuticals is feasible and reproducible to accommodate up to 5 patients per production. In addition, this work also discusses the issues encountered, together with the possible corrective and preventative measures.

64Cu production via the 68Zn(p,nα)64Cu nuclear reaction: An untapped, cost-effective and high energy production route

INTRODUCTION

Copper-64 (64Cu, t1/2 = 12.7 h) is a positron emitter well suited for theranostic applications with beta-emitting 67Cu for targeted molecular imaging and radionuclide therapy. The present work aims to evaluate the radionuclidic purity and radiochemistry of 64Cu produced via the 68Zn(p,nα)64Cu nuclear reaction. Macrocyclic chelators DOTA, NOTA, TETA, and prostate-specific membrane antigen ligand PSMA I&T were radiolabeled with purified 64Cu and tested for in vitro stability. [64Cu]Cu-PSMA I&T was used to demonstrate in vivo PET imaging using 64Cu synthesized via the 68Zn(p,nα)64Cu production route and its suitability as a theranostic imaging partner alongside 67Cu therapy.

METHODS

64Cu was produced on a 24 MeV TR-24 cyclotron at a beam energy of 23.5 MeV and currents up to 70 μA using 200 mg 68Zn encapsulated within an aluminum‑indium-graphite sealed solid target assembly. 64Cu semi-automated purification was performed using a NEPTIS Mosaic-LC synthesis unit employing CU, TBP, and TK201 (TrisKem) resins. Radionuclidic purity was measured by HPGe gamma spectroscopy, while ICP-OES assessed elemental purity. Radiolabeling was performed with NOTA at room temperature and DOTA, TETA, and PSMA I&T at 95 °C. 64Cu incorporation was studied by radio-TLC. 64Cu in vitro stability of [64Cu]Cu-NOTA, [64Cu]Cu-DOTA, [64Cu]Cu-TETA, and [64Cu]Cu-PSMA I&T was assessed at 37 °C from 0 to 72 h in human blood serum. Preclinical PET imaging was performed at 1, 24, and 48 h post-injection with [64Cu]Cu-PSMA I&T in LNCaP tumor-bearing mice and compared with [68Ga]Ga-PSMA I&T.

RESULTS

Maximum purified activity of 4.9 GBq [64Cu]CuCl2 was obtained in 5 mL of pH 2-3 solution, with 2.9 GBq 64Cu concentrated in 0.5 mL. HPGe gamma spectroscopy of purified 64Cu detected <0.3 % co-produced 67Cu at EOB with no other radionuclidic impurities. ICP-OES elemental analysis determined <1 ppm Al, Zn, In, Fe, and Cu in the [64Cu]CuCl2 product. NOTA, DOTA, TETA, and PSMA I&T were radiolabeled with 64Cu, resulting in maximum molar activities of 164 ± 6 GBq/μmol, 155 ± 31 GBq/μmol, 266 ± 34 GBq/μmol, and 117 ± 2 GBq/μmol, respectively. PET imaging in PSMA-expressing LNCaP xenografts resulted in high tumor uptake (SUVmean = 1.65 ± 0.1) using [64Cu]Cu-PSMA I&T, while [68Ga]Ga-PSMA I&T yielded an SUVmean of 0.76 ± 0.14 after 60 min post-injection.

CONCLUSIONS

64Cu was purified in a small volume amenable for radiolabeling, with yields suitable for preclinical and clinical application. The 64Cu production and purification process and the favourable PET imaging properties confirm the 68Zn(p,nα)64Cu nuclear reaction as a viable 64Cu production route for facilities with access to a higher energy proton cyclotron, compared to using expensive 64Ni target material and the 64Ni(p,n)64Cu nuclear reaction.

ADVANCES IN KNOWLEDGE AND IMPLICATIONS FOR PATIENT CARE

Our 64Cu production technique provides an alternative production route with the potential to improve 64Cu availability for preclinical and clinical studies alongside 67Cu therapy.

Radiochemistry for positron emission tomography

Positron emission tomography (PET) constitutes a functional imaging technique that is harnessed to probe biological processes in vivo. PET imaging has been used to diagnose and monitor the progression of diseases, as well as to facilitate drug development efforts at both preclinical and clinical stages. The wide applications and rapid development of PET have ultimately led to an increasing demand for new methods in radiochemistry, with the aim to expand the scope of synthons amenable for radiolabeling. In this work, we provide an overview of commonly used chemical transformations for the syntheses of PET tracers in all aspects of radiochemistry, thereby highlighting recent breakthrough discoveries and contemporary challenges in the field. We discuss the use of biologicals for PET imaging and highlight general examples of successful probe discoveries for molecular imaging with PET - with a particular focus on translational and scalable radiochemistry concepts that have been entered to clinical use.

Preparation of [68Ga]Ga-Chloride from 68Zn solid target for the synthesis of pharmaceutical grade [68Ga]Ga-PSMA-11 and [68Ga]Ga-DOTA-TATE

⁶⁸Ga is produced from enriched zinc-68 target electrodeposited on copper base material which was irradiated with 15 MeV proton energy in 30 MeV cyclotron. A modified semi-automated separation and purification module was used to obtain pharmaceutical grade [⁶⁸Ga]GaCl₃ in 35 ± 5 min. The quality of [⁶⁸Ga]GaCl₃ produced was in accordance with Pharmeuropa 30.4. The [⁶⁸Ga]GaCl₃ was utilized for the formulation of multiple doses of [⁶⁸Ga]Ga-PSMA-11 and [⁶⁸Ga]Ga-DOTATATE. The quality of [⁶⁸Ga]Ga-PSMA-11 and [⁶⁸Ga]Ga-DOTATATE were also in accordance with Pharmacopeia.

68Ga-DOTATATE Prepared from Cyclotron-Produced 68Ga: An Integrated Solution from Cyclotron Vault to Safety Assessment and Diagnostic Efficacy in Neuroendocrine Cancer Patients

Cyclotron production of ⁶⁸Ga is a promising approach to supply ⁶⁸Ga radiopharmaceuticals. To validate this capability, an integrated solution for a robust synthesis of ⁶⁸Ga-DOTATATE prepared from cyclotron-produced ⁶⁸Ga was achieved. A retrospective comparison analysis was performed on patients who underwent PET/CT imaging after injection of DOTATATE labeled with ⁶⁸Ga produced by a cyclotron or eluted from a generator to demonstrate the clinical safety and diagnostic efficacy of the radiopharmaceutical as a routine standard-of-care diagnostic tool in the clinic. Methods: An enriched pressed ⁶⁸Zn target was irradiated by a cyclotron with a proton beam set at 12.7 MeV for 100 min. The fully automated process uses an in-vault dissolution system in which a liquid distribution system transfers the dissolved target to a dedicated hot cell for the purification of ⁶⁸GaCl₃ and radiolabeling of DOTATATE using a cassette-based automated module. Quality control tests were performed on the resulting tracer solution. The internal radiation dose for ⁶⁸Ga-DOTATATE was based on extrapolation from rat biodistribution experiments. A retrospective comparison analysis was performed on patients who underwent PET/CT imaging after injection of DOTATATE labeled with cyclotron- or generator-produced ⁶⁸Ga. Results: The synthesis of ⁶⁸Ga-DOTATATE (20.7 ± 1.3 GBq) with high apparent molar activity (518 ± 32 GBq/μmol at the end of synthesis) was completed in 65 min, and the radiopharmaceutical met the requirements specified in the European Pharmacopoeia monograph on ⁶⁸Ga-chloride (accelerator-produced) solution for radiolabeling. ⁶⁸Ga-DOTATATE was stable for at least 5 h after formulation. The dosimetry calculated with OLINDA for cyclotron- and generator-produced ⁶⁸Ga-DOTATATE was roughly equivalent. The SUV_mean or SUV_max of tumoral lesions with cyclotron-produced ⁶⁸Ga-DOTATATE was equivalent to that with generator-produced ⁶⁸Ga. Among physiologic uptake levels, a significant difference was found in kidneys, spleen, and stomach wall, with lower values in cyclotron-produced ⁶⁸Ga-DOTATATE in all cases. Conclusion: Integrated cyclotron production achieves reliable high yields of clinical-grade ⁶⁸Ga-DOTATATE. The clinical safety and imaging efficacy of cyclotron-produced ⁶⁸Ga-DOTATATE in humans provide supporting evidence for its use in routine clinical practice.

Cyclotron vs generator-produced 68Ga PSMA: a single-institution, prospective clinical trial

The clinical utility of gallium 68 (68Ga)-PSMA PET for the diagnosis and management of prostate cancer is driven in part by radioisotope availability and production costs. This study evaluates the equivalence between the two manufacturing processes for 68Ga-PSMA: 68Ga-PSMA-cyclotron (from a solid target) and 68Ga-PSMA-generator. A prospective, single-arm, single-institution non-randomized study was conducted where 16 patients with prostate adenocarcinoma underwent PET/CTs consecutively within 12 to 48 hours with each type of manufactured 68Ga-PSMA between December 2020 and June 2021. The intraclass correlation coefficients suggested acceptable reliability in all lesion parameters (ICC > 0.70). Bland-Altman analysis demonstrated acceptable bias levels for all lesion parameters. Thereby 68Ga-cyclotron (solid target) and 68Ga-generator production methods tagged to the same PSMA ligand resulted in scans which were deemed to be equivalent in detecting PSMA+ lesions in our study. As cyclotron-produced, solid- target 68Ga can be made in large (Ci) quantities, it is a promising tool for future application in 68Ga-PSMA PET scans with the potential to decrease radiotracer production costs and increase isotope availability.

High-yield cyclotron production of 203Pb using a sealed 205Tl solid target

INTRODUCTION

203Pb (t1/2 = 51.9 h, 279 keV (81 %)) is a diagnostic SPECT imaging radionuclide ideally suited for theranostic applications in combination with 212Pb for targeted alpha particle therapy. Our objectives were to develop a high-yield solid target 203Pb cyclotron production route using isotopically enriched 205Tl target material and the 205Tl(p,3n)203Pb reaction as an alternative to lower energy production via the 203Tl(p,n)203Pb reaction.

METHODS

250 mg 205Tl metal (99.9 % isotopic enrichment) was pressed using a hardened stainless steel die. Aluminum target discs were machined with a central depression and annulus groove. The flattened 205Tl pellet was placed into the central depression of the Al disc and a circle of indium wire was laid in the machined annulus surrounding the pellet. An aluminum foil cover was then pressed onto the target disc to create an airtight bond. Targets were irradiated at 23.3 MeV for up to 516 min on a TR-24 cyclotron at currents up to 60 μA to produce 203Pb via the 205Tl(p,3n)203Pb nuclear reaction. Following a cool-down period of >12 h, the target was removed and 205Tl dissolved in 4 M HNO3. A NEPTIS Mosaic-LC synthesis unit performed automated separation using Eichrom Pb resin, and 203Pb was eluted using 8 M HCl or 1 M NH4OAc. 205Tl was diverted to a vial for recovery in an electrolytic cell. 203Pb product radionuclidic purity was assessed by HPGe gamma spectroscopy, while elemental purity was assessed by ICP-OES. Radiolabeling and stability studies were performed with PSC, TCMC, and DOTA chelators, and 203Pb incorporation was verified by radio-TLC analysis.

RESULTS

Cyclotron irradiations performed at 60 μA proton beam current and 23.3 MeV (205Tl incident energy) had a 203Pb saturated yield of 4658 ± 62 MBq/μA (n = 3). Automated NEPTIS separation took <4 h from the start of target dissolution to product elution, yielding >85 % decay-corrected [203Pb]PbCl2 with a radionuclidic purity of >99.9 %. Purified [203Pb]PbCl2 yields of up to 12 GBq 203Pb were attained (15.8 GBq at EOB). The [203Pb]PbCl2 and [203Pb]Pb(OAc)2 products contained no detectable radionuclidic impurities besides 201Pb (<0.1 %), and <0.4 ppm stable Pb. 205Tl metal was recovered with a 92 % batch yield. Aliquots of 100 μL [203Pb]Pb(OAc)2 were used for radiolabeling PSC-Bn-NCS, TCMC-NCS, and DOTA-NCS chelators at pH 4.5 and 22 °C for 30 min, with maximum respective molar activities of 461 ± 30 GBq/μmol, 195 ± 37 GBq/μmol, and 83 ± 12 GBq/μmol. PSC, TCMC, and DOTA chelators exhibited >99.9 % incorporation after a 120-hour incubation in human serum at 37 °C.

CONCLUSIONS

Nuclear medicine centers with access to higher energy cyclotrons can produce large 203Pb activities sufficient for clinical applications, with a convenient separation technique producing highly pure [203Pb]PbCl2 or [203Pb]Pb(OAc)2 for direct radiolabeling. This represents an attractive route to produce 203Pb for diagnostic SPECT imaging alongside 212Pb targeted alpha particle therapy.

ADVANCES IN KNOWLEDGE AND IMPLICATIONS FOR PATIENT CARE

Our high-yield 203Pb production technique significantly enhances 203Pb production capabilities to meet the growing preclinical and clinical demand for 203Pb radiopharmaceuticals alongside 212Pb target alpha particle therapy.

Cyclotron Production of Gallium-68 Radiopharmaceuticals Using the 68Zn(p,n)68Ga Reaction and Their Regulatory Aspects

Designing and implementing various radionuclide production methods guarantees a sustainable supply, which is important for medical use. The use of medical cyclotrons for radiometal production can increase the availability of gallium-68 (⁶⁸Ga) radiopharmaceuticals. Although generators have greatly influenced the demand for ⁶⁸Ga radiopharmaceuticals, the use of medical cyclotrons is currently being explored. The resulting ⁶⁸Ga production is several times higher than obtained from a generator. Moreover, the use of solid targets yields end of purification and end of synthesis (EOS) of up to 194 GBq and 72 GBq, respectively. Furthermore, experiments employing liquid targets have provided promising results, with an EOS of 3 GBq for [⁶⁸Ga]Ga-PSMA-11. However, some processes can be further optimized, specifically purification, to achieve high ⁶⁸Ga recovery and apparent molar activity. In the future, ⁶⁸Ga will probably remain one of the most in-demand radionuclides; however, careful consideration is needed regarding how to reduce the production costs. Thus, this review aimed to discuss the production of ⁶⁸Ga radiopharmaceuticals using Advanced Cyclotron Systems, Inc. (ACSI, Richmond, BC, Canada) Richmond, Canada and GE Healthcare, Wisconsin, USA cyclotrons, its related factors, and regulatory concerns.

Recovery of Gallium-68 and Zinc from HNO3-Based Solution by Liquid-Liquid Extraction with Arylamino Phosphonates

The cyclotron production of gallium-68 via the ⁶⁸Zn(p,n)⁶⁸Ga nuclear reaction in liquid targets is gaining significant traction in clinics. This work describes (1) the synthesis of new arylamino phosphonates via the Kabachnik-Fields reaction, (2) their use for liquid-liquid extraction of ⁶⁸Ga from 1 M Zn(NO₃)₂/0.01 M HNO₃ in batch and continuous flow, and (3) the use of Raman spectroscopy as a process analytical technology (PAT) tool for in-line measurement of ⁶⁸Zn. The highest extraction efficiencies were obtained with the extractants functionalized with trifluoromethyl substituents and ethylene glycol ponytails, which were able to extract up to 90% of gallium-68 in batch and 80% in flow. Only ppm amounts of zinc were co-extracted. The extraction efficiency was a function of pKa and the aqueous solubility of the extractant and showed marked concentration, solvent, and temperature dependence. Raman spectroscopy was found to be a promising PAT tool for the continuous production of gallium-68.

Good practices for 68Ga radiopharmaceutical production

Background

The radiometal gallium-68 (⁶⁸Ga) is increasingly used in diagnostic positron emission tomography (PET), with ⁶⁸Ga-labeled radiopharmaceuticals developed as potential higher-resolution imaging alternatives to traditional ^99mTc agents. In precision medicine, PET applications of ⁶⁸Ga are widespread, with ⁶⁸Ga radiolabeled to a variety of radiotracers that evaluate perfusion and organ function, and target specific biomarkers found on tumor lesions such as prostate-specific membrane antigen, somatostatin, fibroblast activation protein, bombesin, and melanocortin.

Main body

These ⁶⁸Ga radiopharmaceuticals include agents such as [⁶⁸Ga]Ga-macroaggregated albumin for myocardial perfusion evaluation, [⁶⁸Ga]Ga-PLED for assessing renal function, [⁶⁸Ga]Ga-t-butyl-HBED for assessing liver function, and [⁶⁸Ga]Ga-PSMA for tumor imaging. The short half-life, favourable nuclear decay properties, ease of radiolabeling, and convenient availability through germanium-68 (⁶⁸Ge) generators and cyclotron production routes strongly positions ⁶⁸Ga for continued growth in clinical deployment. This progress motivates the development of a set of common guidelines and standards for the ⁶⁸Ga radiopharmaceutical community, and recommendations for centers interested in establishing ⁶⁸Ga radiopharmaceutical production.

Conclusion

This review outlines important aspects of ⁶⁸Ga radiopharmacy, including ⁶⁸Ga production routes using a ⁶⁸Ge/⁶⁸Ga generator or medical cyclotron, standardized ⁶⁸Ga radiolabeling methods, quality control procedures for clinical ⁶⁸Ga radiopharmaceuticals, and suggested best practices for centers with established or upcoming ⁶⁸Ga radiopharmaceutical production. Finally, an outlook on ⁶⁸Ga radiopharmaceuticals is presented to highlight potential challenges and opportunities facing the community.

Comparing the clinical performance and cost efficacy of [68Ga]Ga-PSMA-11 and [18F]PSMA-1007 in the diagnosis of recurrent prostate cancer: a Markov chain decision analysis

PURPOSE

Amongst others, [68Ga]Ga-PSMA-11 and [18F]PSMA-1007 are available for the detection of recurrent prostate cancer (rPC). There are currently limited data comparing the performance of these two radioligands with respect to clinical outcomes or their cost efficacy, which this study aims to address.

METHODS

Two hundred and forty-four patients undergoing PSMA PET/CT for rPC were retrospectively analysed for this study (one hundred and twenty two with each radiopharmaceutical) to generate rates of PET positivity, negativity and unclear findings. Patients underwent follow-up to determine the rate of additional examinations and to confirm PET findings. A Markov chain decision analysis was implemented to model clinical decision-making processes and to analyse clinical performance of the two tracers. We determine their clinical cost efficacies using cost data from several countries where both radiotracers are in routine use.

RESULTS

The PET positivity rate was non-significantly higher for [18F]PSMA-1007 compared to [68Ga]Ga-PSMA-11 (91.8% vs. 86.9%, p = 0.68), whereas the rate of uncertain findings was significantly greater (17.2% vs. 8.25%, p = 0.02). The probability of a true positive finding was higher for [68Ga]Ga-PSMA-11 (0.90, 95% CI 0.70-0.98) vs. [18F]PSMA-1007 (0.81, 95% CI 0.66-0.91). A significantly (p < 0.0001) higher PPV for [68Ga]Ga-PSMA-11 (0.99, 95% CI 0.99-1.0 vs. 0.86) was found compared to [18F]PSMA-1007 (0.86, 95% CI 0.82-1.00). Intervention efficacy analysis favoured [68Ga]Ga-PSMA-11, where the number needed to image (to achieve a true positive finding) was 10.58 and the number needed to image to harm (to achieve a false positive finding) was - 8.08. A cost efficacy analysis favours [68Ga]Ga-PSMA-11 in three of the four jurisdictions analysed where health economic data was available (Switzerland, Israel, Australia) and [18F]PSMA-1007 in one jurisdiction (Denmark).

CONCLUSION

The analysis reveals a non-significantly higher PET positivity rate for [18F]PSMA-1007, but finds significantly greater rates of uncertain findings and false positive findings when compared to [68Ga]Ga-PSMA-11. We find differences in the two tracers in terms of clinical performance and cost efficacy. The method presented herein is generalisable and can be used with clinical or cost data for other countries or tracers.

Production Review of Accelerator-Based Medical Isotopes

The production of reactor-based medical isotopes is fragile, which has meant supply shortages from time to time. This paper reviews alternative production methods in the form of cyclotrons, linear accelerators and neutron generators. Finally, the status of the production of medical isotopes in China is described.

First In Vivo and Phantom Imaging of Cyclotron-Produced 133La as a Theranostic Radionuclide for 225Ac and 135La

Theranostic isotope pairs have gained recent clinical interest because they can be labeled to the same tracer and applied for diagnostic and therapeutic purposes. The goals of this study were to investigate cyclotron production of clinically relevant 133La activities using natural and isotopically enriched barium target material, compare fundamental PET phantom imaging characteristics of 133La with those of common PET radionuclides, and demonstrate in vivo preclinical PET tumor imaging using 133La-PSMA-I&T. Methods:133La was produced on a 24-MeV cyclotron using an aluminum-indium sealed target with 150-200 mg of isotopically enriched 135BaCO3, natBaCO3, and natBa metal. A synthesis unit performed barium/lanthanum separation. DOTA, PSMA-I&T, and macropa were radiolabeled with 133La. Derenzo and National Electrical Manufacturers Association phantom imaging was performed with 133La, 132La, and 89Zr and compared with 18F, 68Ga, 44Sc, and 64Cu. In vivo preclinical imaging was performed with 133La-PSMA-I&T on LNCaP tumor-bearing mice. Results: Proton irradiations for 100 µA·min at 23.3 MeV yielded 214 ± 7 MBq of 133La and 28 ± 1 MBq of 135La using 135BaCO3, 59 ± 2 MBq of 133La and 35 ± 1 MBq of 135La using natBaCO3, and 81 ± 3 MBq of 133La and 48 ± 1 MBq of 135La using natBa metal. At 11.9 MeV, 135La yields were 81 ± 2 MBq, 6.8 ± 0.4 MBq, and 9.9 ± 0.5 MBq for 135BaCO3, natBaCO3, and natBa metal. BaCO3 target material recovery was 95.4% ± 1.7%. National Electrical Manufacturers Association and Derenzo phantom imaging demonstrated that 133La PET spatial resolution and scanner recovery coefficients were superior to those of 68Ga and 132La and comparable to those of 89Zr. The apparent molar activity was 130 ± 15 GBq/µmol with DOTA, 73 ± 18 GBq/µmol with PSMA-I&T, and 206 ± 31 GBq/µmol with macropa. Preclinical PET imaging with 133La-PSMA-I&T provided high-resolution tumor visualization with an SUV of 0.97 ± 0.17 at 60 min. Conclusion: With high-yield 133La cyclotron production, recovery of BaCO3 target material, and fundamental imaging characteristics superior to those of 68Ga and 132La, 133La represents a promising radiometal candidate to provide high-resolution PET imaging as a PET/α-therapy theranostic pair with 225Ac or as a PET/Auger electron therapy theranostic pair with 135La.

Reactions of methyl, hydroxyl and peroxyl radicals with the DOTA chelating agent used in medical imaging

The mechanism of reaction of DOTA (1,4,7,10-tetraazacyclododecane-1,4,7,10-tetraacetic acid) with ·CH₃, CH₃O₂· and ·OH radicals were studied. The radicals were formed in situ radiolytically. The methyl radicals react orders of magnitude slower with DOTA and with M^III(DOTA)^- than the hydroxyl radicals. The various final products were identified and mechanisms for their formation are proposed. CH₃O₂· radicals do not react, or react too slowly to be observed, with DOTA and with M^III(DOTA)^- as long as the central cation is not oxidized by the peroxyl radical. The results imply that synthesis of the M^III(DOTA)^-(M^III = radioisotope) complexes in a water-organic solvent (ethanol or 2-propanol or acetonitrile) mixture is not only kinetically desired but the so formed complex also decreases the radiolytic decomposition of DOTA.

Methods for the Determination of Transition Metal Impurities in Cyclotron-Produced Radiometals

Cyclotron-produced radiometals must be separated from the irradiated target and purified from other metal impurities, which could interfere with the radiolabeling process. We compared different chromatographic and colorimetric methods to determine the amount of transition metals in radioactive samples. Besides commercially available colorimetric tests, 4-(2-pyridylazo)resorcinol and xylenol orange were used as a non-selective metal reagents, forming water-soluble chelates with most of the transition metals immediately. We compared the applicability of pre- and post-column derivatization, as well as colorimetric determination without separation. The studied chromatographic and colorimetric analyses are not suitable to completely replace atomic spectroscopic techniques for the determination of metal contaminants in radioactive samples, but they may play an important role in the development of methods for the purification of radiometals and in their routine quality control.

Advancement in production of radiotracers

After introduction of the first commercial combined PET and/or CT technology in 2001, this diagnostic tool quickly became a clinical success and was considered the fastest growing diagnostic imaging technology ever. However, this technique is very dependent on the availability of positron emitting isotopes and radiochemistry to incorporate the radioactive isotopes into larger molecules of physiological interest. Within this review article a historical overview starting with the first applications of positron emitting isotopes in the 1930's is presented. Afterwards a more detailed presentation summarizing the physical basis and advancements in cyclotron technology is given. Radiochemical and/or pharmaceutical advancements are presented systematically for the most significant isotopes like ¹⁵O, ¹³N, ¹¹C, ¹⁸F and ⁶⁸Ga Besides these major PET isotopes, advancements of other radio-metals and future perspectives regarding application of new radionuclides will be discussed. Finally, very interesting new and compact accelerator technology and microfluidic chemical reaction approaches will be discussed. Especially, new compact accelerator technology might be new quantum leap within this radiodiagnostic technology and might result in even further prevalence, ultimately envisioned by the dose-on-demand concept that will be briefly discussed.

Demystifying solid targets: Simple and rapid distribution-scale production of [68Ga]GaCl3 and [68Ga]Ga-PSMA-11

BACKGROUND

As the demand for ⁶⁸Ga continues to grow, there is increasing interest in single-to-multi-Curie production quantities of both [⁶⁸Ga]GaCl₃ and tracers such as [⁶⁸Ga]Ga-PSMA-11. While such quantities are possible with solid targets, this implementation is often challenging as it typically requires significant site expertise for solid target processing and careful operator-dependent synchronization of multiple independent time-sensitive chemistry steps. Herein we focus on a fully automated solid target production and purification process whereby we avoid the need for tongs/tele-pliers, and have simplified the chemistry by implementing a single sequence (i.e. "time-list") to execute cassette-based dissolution, purification, and labeling.

METHODS

Electroplated ⁶⁸Zn was irradiated in a PETtrace prototype automated solid target system. Following irradiation, and using a single FASTlab time-list, the ⁶⁸Zn was automatically dissolved with HCl/H₂O₂ and purified as [⁶⁸Ga]GaCl₃ using a combination of resins (ZR/TK400, A8, TK200: Triskem). For select experiments, [⁶⁸Ga]Ga-PSMA-11 was also produced on the same cassette/single time-list (N = 4), or, by kit labeling (N = 1). Efforts focused towards on-cassette production of [⁶⁸Ga]GaCl₃ strived to maximize activity and quality, whereas efforts focused towards on-cassette production of [⁶⁸Ga]Ga-PSMA-11 aimed at limiting the entire production cycle to 1 h including the irradiation time (i.e. start-of-bombardment ➔ end-of-synthesis [EOS]).

RESULTS

For the high activity triplicate [⁶⁸Ga]GaCl₃ productions (i.e. 80 μA, 102 min, 216 ± 10 mg), [⁶⁸Ga]GaCl₃ was purified (end-of-bombardment ➔ end-of-purification [EOP]) in ~28 min with activity yields of 181 ± 8 GBq at EOP and average radiochemical yields of 66 ± 5%. Average AMAs of 2.26 ± 0.16 TBq/μmol using DOTA (N = 3) and 12.00 TBq/μmol using HBED (PSMA-11) (N = 1) at EOP were measured. For the single kit test, (80 μA, 120 min, 263 mg ⁶⁸Zn) for which 18 mg ascorbic acid was added to the buffer, 199 GBq of [⁶⁸Ga]Ga-PSMA-11 was successfully produced (thin layer chromatography-based radiochemical purity >99% at 6 h EOS). Finally, for efforts focused at expedient [⁶⁸Ga]Ga-PSMA-11, up to 42 GBq [⁶⁸Ga]Ga-PSMA-11 with a radiochemical yield of 51.2% was produced in 63 min, including beamtime, using 220 mg of ⁶⁸Zn as target material.

CONCLUSION

With the goal of simplifying solid target production and purification efforts, automated methods using single-use, cassette-based approaches for rapid, large-scale, single time-list production of [⁶⁸Ga]GaCl₃ and [⁶⁸Ga]Ga-PSMA-11 were developed. These methods were simple to execute and yielded high quality multi-Curie levels of both [⁶⁸Ga]GaCl₃ and [⁶⁸Ga]Ga-PSMA-11.

Investigation of a Possible Material-Saving Approach of Sputtering Techniques for Radiopharmaceutical Target Production

Magnetron sputtering (MS) is a relatively new deposition technique, which is being considered among the cyclotron solid target (CST) manufacturing options now available, aiming at the medical radioisotopes yield for radiopharmaceutical production. However, the intrinsic high material losses during the deposition process do not permit its use with extremely expensive target materials, such as isotopically enriched metals/oxides. In this study, R&D technology for a new recovering shield is instead proposed to assess the dissipation of target material during the sputtering processes and, thus, an estimate of the material recovery that may be feasible and the related amount. The weight-loss analysis method is used to assess the material losses level inside the chamber during processing. In all tests carried out, a high-purity copper (99.99%) was used as a target material. As a result of this study, the material distribution for both magnetron and diode sputtering depositions can be calculated. The feasibility of the ultra-thick coatings growing, devoted to CST production, is demonstrated.

Expanding the PET radioisotope universe utilizing solid targets on small medical cyclotrons

Molecular imaging with medical radioisotopes enables the minimally-invasive monitoring of aberrant biochemical, cellular and tissue-level processes in living subjects. The approach requires the administration of radiotracers composed of radioisotopes attached to bioactive molecules, the pairing of which considers several aspects of the radioisotope in addition to the biological behavior of the targeting molecule to which it is attached. With the advent of modern cellular and biochemical techniques, there has been a virtual explosion in potential disease recognition antigens as well as targeting moieties, which has subsequently opened new applications for a host of emerging radioisotopes with well-matched properties. Additionally, the global radioisotope production landscape has changed rapidly, with reactor-based production and its long-defined, large-scale centralized manufacturing and distribution paradigm shifting to include the manufacture and distribution of many radioisotopes via a worldwide fleet of cyclotrons now in operation. Cyclotron-based radioisotope production has become more prevalent given the commercial availability of instruments, coupled with the introduction of new target hardware, process automation and target manufacturing methods. These advances enable sustained, higher-power irradiation of solid targets that allow hospital-based radiopharmacies to produce a suite of radioisotopes that drive research, clinical trials, and ultimately clinical care. Over the years, several different radioisotopes have been investigated and/or selected for radiolabeling due to favorable decay characteristics (i.e. a suitable half-life, high probability of positron decay, etc.), well-elucidated chemistry, and a feasible production framework. However, longer-lived radioisotopes have surged in popularity given recent regulatory approvals and incorporation of radiopharmaceuticals into patient management within the medical community. This review focuses on the applications, nuclear properties, and production and purification methods for some of the most frequently used/emerging positron-emitting, solid-target-produced radioisotopes that can be manufactured using small-to-medium size cyclotrons (≤24 MeV).

Clinically Applicable Cyclotron-Produced Gallium-68 Gives High-Yield Radiolabeling of DOTA-Based Tracers

By using solid targets in medical cyclotrons, it is possible to produce large amounts of ⁶⁸GaCl₃. Purification of Ga³⁺ from metal ion impurities is a critical step, as these metals compete with Ga³⁺ in the complexation with different chelators, which negatively affects the radiolabeling yields. In this work, we significantly lowered the level of iron (Fe) impurities by adding ascorbate in the purification, and the resulting ⁶⁸GaCl₃ could be utilized for high-yield radiolabeling of clinically relevant DOTA-based tracers. ⁶⁸GaCl₃ was cyclotron-produced and purified with ascorbate added in the wash solutions through the UTEVA resins. The ⁶⁸Ga eluate was analyzed for radionuclidic purity (RNP) by gamma spectroscopy, metal content by ICP-MS, and by titrations with the chelators DOTA, NOTA, and HBED. The ⁶⁸GaCl₃ eluate was utilized for GMP-radiolabeling of the DOTA-based tracers DOTATOC and FAPI-46 using an automated synthesis module. DOTA chelator titrations gave an apparent molar activity (AMA) of 491 ± 204 GBq/µmol. GMP-compliant syntheses yielded up to 7 GBq/batch [⁶⁸Ga]Ga-DOTATOC and [⁶⁸Ga]Ga-FAPI-46 (radiochemical yield, RCY ~ 60%, corresponding to ten times higher compared to generator-based productions). Full quality control (QC) of ⁶⁸Ga-labelled tracers showed radiochemically pure and stable products at least four hours from end-of-synthesis.

Recent Advances in the Clinical Translation of Silicon Fluoride Acceptor (SiFA) 18F-Radiopharmaceuticals

The incorporation of silicon fluoride acceptor (SiFA) moieties into a variety of molecules, such as peptides, proteins and biologically relevant small molecules, has improved the generation of ¹⁸F-radiopharmaceuticals for medical imaging. The efficient isotopic exchange radiofluorination process, in combination with the enhanced [¹⁸F]SiFA in vivo stability, make it a suitable strategy for fluorine-18 incorporation. This review will highlight the clinical applicability of [¹⁸F]SiFA-labeled compounds and discuss the significant radiotracers currently in clinical use.

Production of a broad palette of positron emitting radioisotopes using a low-energy cyclotron: Towards a new success story in cancer imaging?

Over the last several years, positron emission tomography (PET) has matured as an indispensable component of cancer diagnostics. Owing to the large variability observed among the cancer patients and the need to personalize individual patient's diagnosis and treatment, the need for new positron emitting radioisotopes has continued to grow. This mini review opens with a brief introduction to the criteria for radioisotope selection for PET imaging. Subsequently, positron emitting radioisotopes are categorized as: established, emerging and futuristic, based on the stages of their advancement. The production methodologies and the radiochemical separation procedures for obtaining the important radioisotopes in a form suitable for preparation of radiopharmaceuticals for PET imaging are briefly discussed.

Applications of Radiolabelled Curcumin and Its Derivatives in Medicinal Chemistry

Curcumin is a natural occurring molecule that has aroused much interest among researchers over the years due to its pleiotropic set of biological properties. In the nuclear medicine field, radiolabelled curcumin and curcumin derivatives have been studied as potential radiotracers for the early diagnosis of Alzheimer’s disease and cancer. In the present review, the synthetic pathways, labelling methods and the preclinical investigations involving these radioactive compounds are treated. The studies entailed chemical modifications for enhancing curcumin stability, as well as its functionalisation for the labelling with several radiohalogens or metal radionuclides (fluorine-18, technetium-99m, gallium-68, etc.). Although some drawbacks have yet to be addressed, and none of the radiolabelled curcuminoids have so far achieved clinical application, the studies performed hitherto provide useful insights and lay the foundation for further developments.

Prostate Cancer Theranostics: From Target Description to Imaging

Prostate-specific membrane antigen-PET/computed tomography (PSMA-PET/CT) is the investigation of choice for imaging prostate cancer. Demonstrating high diagnostic accuracy, PSMA-PET/CT detects disease at very early stages of recurrence, where the chances of a definitive cure may be at their greatest. A number of PSMA-radioligands are in established clinical routine, and there are currently only limited data and no single tracer can clearly be advocated over the others at present. Further clinical trial data, comparing and contrasting radiotracers and reporting outcome-based data are necessary to further increase the implementation of this very promising imaging modality.

Radiolabeling Optimization and Preclinical Evaluation of the New PSMA Imaging Agent [18F]AlF-P16-093

Prostate-specific membrane antigen (PSMA)-targeted radioligands have played an increasing role in the diagnosis of prostate cancer. [68Ga]Ga-P16-093 is a PSMA-targeting agent for positron emission tomography imaging, currently under a Phase 2 clinical trial. In the present study, P16-093 was labeled with 18F via [18F]AlF2+ complex formation, and the biological properties of [18F]AlF-P16-093 were evaluated. Optimization of radiolabeling efficiency was performed by testing a series of parameters, including the amount of free ligand; the amount of Al3+; and the influence of solvent, pH, temperature, reaction time, and reaction volume. Optimal labeling results were achieved at pH 5 by reacting at 60 °C for 15 min in a vial containing 74-370 MBq of [18F]fluoride, 46 nmol of P16-093, 40 nmol of AlCl3·6 H2O, and 50% EtOH. [18F]AlF-P16-093 was prepared with a non-decay-corrected radiochemical yield of 54.4 ± 4.4% (n = 9) within 30 min (final radiochemical purity ≥95%). In vitro, [18F]AlF-P16-093 showed PSMA-specific high uptakes in PIP-PC3 cells. The binding affinity of [18F]AlF-P16-093 to PSMA was determined as Kd of 12.4 ± 2.0 nM. The tumor uptake in mice with a xenografted PSMA-expressing PIP-PC3 tumor was high (18.8 ± 5.14% ID/g at 1 h postinjection) and retained without washout for 2 h. In addition, tumor uptake was almost completely blocked by coinjecting a PSMA inhibitor, 2-PMPA. The bone activity at 1 h post injection was higher with [18F]AlF-P16-093 (2.83 ± 0.49% ID/g) in comparison to that of [68Ga]Ga-P16-093 (0.26 ± 0.07% ID/g). In summary, an efficient and simple radiosynthesis of [18F]AlF-P16-093 was achieved. [18F]AlF-P16-093 showed desirable in vivo pharmacokinetics and excellent PSMA-targeting properties for imaging PSMA expression in prostate cancer.

Recent Breakthrough in 68Ga-Radiopharmaceuticals Cold Kits for Convenient PET Radiopharmacy

⁶⁸Ga-PET has emerged as an important diagnostic tool for precise detection and monitoring of oncological situations. Availability, cost, and radiosynthesis procedure are determining steps for success of a radioisotope/radiopharmaceutical in nuclear medicine. Availability of ⁶⁸Ga from a ⁶⁸Ge/⁶⁸Ga generator containing a long-lived parent radioisotope (⁶⁸Ge: t_1/2 = 271 days) and an inexpensive, simplified production of ⁶⁸Ga-radiopharmaceuticals through kit methodology has allowed smooth accommodation of ⁶⁸Ga-PET in clinics. The uncomplicated formulation of ⁶⁸Ga-radiopharmaceuticals from a lyophilized, cold kit is an impending breakthrough in clinical PET. The huge success of ⁶⁸Ga in neuroendocrine tumor and prostate cancer imaging along with the regulatory approval of respective cold kits has opened a pathway for development of kits for other evolving radiotracers. There is a definite scope for increased participation of commercial manufacturers and distributors of cold kits to spread the potential of ⁶⁸Ga worldwide across all the geographical locations and satellite centers.

Multi-curie production of gallium-68 on a biomedical cyclotron and automated radiolabelling of PSMA-11 and DOTATATE

BACKGROUND

With increasing clinical demand for gallium-68, commercial germanium-68/gallium-68 ([⁶⁸Ge]Ge/[⁶⁸Ga]Ga) generators are incapable of supplying sufficient amounts of the short-lived daughter isotope. In this study, we demonstrate a high-yield, automated method for producing multi-Curie levels of [⁶⁸Ga]GaCl₃ from solid zinc-68 targets and subsequent labelling to produce clinical-grade [⁶⁸Ga]Ga-PSMA-11 and [⁶⁸Ga]Ga-DOTATATE.

RESULTS

Enriched zinc-68 targets were irradiated at up to 80 µA with 13 MeV protons for 120 min; repeatedly producing up to 194 GBq (5.24 Ci) of purified gallium-68 in the form of [⁶⁸Ga]GaCl₃ at the end of purification (EOP) from an expected > 370 GBq (> 10 Ci) at end of bombardment. A fully automated dissolution/separation process was completed in 35 min. Isolated product was analysed according to the Ph. Eur. monograph for accelerator produced [⁶⁸Ga]GaCl₃ and found to comply with all specifications. In every instance, the radiochemical purity exceeded 99.9% and importantly, the radionuclidic purity was sufficient to allow for a shelf-life of up to 7 h based on this metric alone. Fully automated production of up to 72.2 GBq [⁶⁸Ga]Ga-PSMA-11 was performed, providing a product with high radiochemical purity (> 98.2%) and very high apparent molar activities of up to 722 MBq/nmol. Further, manual radiolabelling of up to 3.2 GBq DOTATATE was performed in high yields (> 95%) and with apparent molar activities (9-25 MBq/nmol) sufficient for clinical use.

CONCLUSIONS

We have developed a high-yielding, automated method for the production of very high amounts of [⁶⁸Ga]GaCl₃, sufficient to supply proximal radiopharmacies. The reported method led to record-high purified gallium-68 activities (194 GBq at end of purification) and subsequent labelling of PSMA-11 and DOTATATE. The process was highly automated from irradiation through to formulation of the product, and as such comprised a high level of radiation protection. The quality control results obtained for both [⁶⁸Ga]GaCl₃ for radiolabelling and [⁶⁸Ga]Ga-PSMA-11 are promising for clinical use.

High yield cyclotron production of a novel 133/135La theranostic pair for nuclear medicine

This study reports the high-yield production of a novel ^133/135La theranostic pair at a 22 MeV proton beam energy as an attractive alternative to the recently introduced ^132/135La pair, demonstrating over an order of magnitude production increase of ^133/135La (231 ± 8 MBq ¹³³La and 166 ± 5 MBq ¹³⁵La at End of Bombardment (EOB)) compared to 11.9 MeV production of ^132/135La (0.82 ± 0.06 MBq ¹³²La and 19.0 ± 1.2 MBq ¹³⁵La) for 500 µA·min irradiations. A new sealed solid cyclotron target is introduced, which is fast to assemble, easy to handle, storable, and contains reusable components. Radiolabeling with macrocyclic chelators DOTA and macropa achieved full incorporation, with respective apparent ¹³³La molar activites of 33 ± 5 GBq/µmol and 30 ± 4 GBq/µmol. PET centers with access to a 22 MeV capable cyclotron could produce clinically-relevant doses of ^133/135La, via ^natBa irradiation, as a standalone theranostic agent for PET imaging and Auger electron therapy. With lower positron energies and less energetic and abundant gamma rays than ⁶⁸Ga, ⁴⁴Sc and ¹³²La, ¹³³La appears to be an attractive radiometal candidate for PET applications requiring a higher scanning resolution, a relatively long isotopic half-life, ease of handling, and a low patient dose.

Automated production of [18F]SiTATE on a Scintomics GRP™ platform for PET/CT imaging of neuroendocrine tumors

INTRODUCTION

[¹⁸F]SiTATE (formerly known as [¹⁸F]SiFAlin-TATE) was recently introduced as a highly promising imaging agent for the diagnosis of well-differentiated neuroendocrine tumors (NET) using positron emission tomography/computed tomography (PET/CT). A high tumor uptake and excellent image quality, the straightforward labeling approach, as well as the economic and logistic advantages of ¹⁸F- over ⁶⁸Ga-labeled compounds predestinate [¹⁸F]SiTATE to become a potential new clinical reference standard. A novel state-of-the-art methodology of automated radiopharmaceutical production is required to establish [¹⁸F]SiTATE in clinical routine. This work illustrates the development of a novel synthesis procedure of [¹⁸F]SiTATE on an automated synthesis unit (ASU) and the clinical applicability of the tracer in human NET imaging.

METHODS

A new synthesis protocol was generated for the production of [¹⁸F]SiTATE on the Scintomics GRP™ platform for clinical NET imaging. The synthesis was carried out according to common Good Manufacturing Practice (GMP) guidelines including all quality control measurements. To confirm utility, clinical batches (n = 3) were produced and applied to six patients diagnosed with NET.

RESULTS

[¹⁸F]SiTATE was obtained in 54 ± 4% (n = 3) non-decay corrected radiochemical yield (RCY), with a radiochemical purity of 96.3 ± 0.1% and a molar activity (A_m) of 472 ± 45 GBq/μmol (n = 3). Quality control measurements always met the local release criteria. All specifications were taken or adapted from the Ph.Eur. regulations. PET/CT imaging with [¹⁸F]SiTATE produced on the GRP™ module confirmed the expected high image quality. The in vivo distribution pattern and excellent tumor to non-tumor contrast observed, matched the quality of the manually prepared [¹⁸F]SiTATE batches.

CONCLUSIONS

The automated manufacture of [¹⁸F]SiTATE was developed using the Scintomics GRP™ platform. The high quality of the radiotracer matched stringent quality control requirements adhering to common GMP guidelines, and its clinical applicability was confirmed by human PET/CT investigations.

ADVANCES IN KNOWLEDGE AND IMPLICATIONS FOR PATIENT CARE

The automated process for the manufacture of [¹⁸F]SiTATE described herein represents an important contribution to make [¹⁸F]SiTATE routinely accessible for its use in clinical NET diagnosis.