Zirconium molybdate gel as a generator for technetium-99m--I. The concept and its evaluation

New strategies for a sustainable 99mTc supply to meet increasing medical demands: Promising solutions for current problems

The continuing rapid expansion of ^99mTc diagnostic agents always calls for scaling up ^99mTc production to cover increasing clinical demand. Nevertheless, ^99mTc availability depends mainly on the fission-produced ⁹⁹Mo supply. This supply is seriously influenced during renewed emergency periods, such as the past ⁹⁹Mo production crisis or the current COVID-19 pandemic. Consequently, these interruptions have promoted the need for ^99mTc production through alternative strategies capable of providing clinical-grade ^99mTc with high purity. In the light of this context, this review illustrates diverse production routes that either have commercially been used or new strategies that offer potential solutions to promote a rapid production growth of ^99mTc. These techniques have been selected, highlighted, and evaluated to imply their impact on developing ^99mTc production. Furthermore, their advantages and limitations, current situation, and long-term perspective were also discussed. It appears that, on the one hand, careful attention needs to be devoted to enhancing the ⁹⁹Mo economy. It can be achieved by utilizing ⁹⁸Mo neutron activation in commercial nuclear power reactors and using accelerator-based ⁹⁹Mo production, especially the photonuclear transmutation strategy. On the other hand, more research efforts should be devoted to widening the utility of ⁹⁹Mo/^99mTc generators, which incorporate nanomaterial-based sorbents and promote their development, validation, and full automization in the near future. These strategies are expected to play a vital role in providing sufficient clinical-grade ^99mTc, resulting in a reasonable cost per patient dose.

Sorption Profile of Low Specific Activity 99Mo on Nanoceria-Based Sorbents for the Development of 99mTc Generators: Kinetics, Equilibrium, and Thermodynamic Studies

⁹⁹Mo/^99mTc generators play a significant role in supplying ^99mTc for diagnostic interventions in nuclear medicine. However, the applicability of using low specific activity (LSA) ⁹⁹Mo asks for sorbents with high sorption capacity. Herein, this study aims to evaluate the sorption behavior of LSA ⁹⁹Mo towards several CeO₂ nano-sorbents developed in our laboratory. These nanomaterials were prepared by wet chemical precipitation (CP) and hydrothermal (HT) approaches. Then, they were characterized using XRD, BET, FE-SEM, and zeta potential measurements. Additionally, we evaluated the sorption profile of carrier-added (CA) ⁹⁹Mo onto each material under different experimental parameters. These parameters include pH, initial concentration of molybdate solution, contact time, and temperature. Furthermore, the maximum sorption capacities were evaluated. The results reveal that out of the synthesized CeO₂ nanoparticles (NPs) materials, the sorption capacity of HT-1 and CP-2 reach 192 ± 10 and 184 ± 12 mg Mo·g^–1, respectively. For both materials, the sorption kinetics and isotherm data agree with the Elovich and Freundlich models, respectively. Moreover, the diffusion study demonstrates that the sorption processes can be described by pore diffusion (for HT-synthesis route 1) and film diffusion (for CP-synthesis route 2). Furthermore, the thermodynamic parameters indicate that the Mo sorption onto both materials is a spontaneous and endothermic process. Consequently, it appears that HT-1 and CP-2 have favorable sorption profiles and high sorption capacities for CA-⁹⁹Mo. Therefore, they are potential candidates for producing a ⁹⁹Mo/^99mTc radionuclide generator by using LSA ⁹⁹Mo.

Synthesis and Physical Property Characterisation of Spheroidal and Cuboidal Nuclear Waste Simulant Dispersions

This study investigated dispersions analogous to highly active nuclear waste, formed from the reprocessing of Spent Nuclear Fuel (SNF). Non-radioactive simulants of spheroidal caesium phosphomolybdate (CPM) and cuboidal zirconium molybdate (ZM-a) were successfully synthesised; confirmed via Scanning Electron Microscopy (SEM), powder X-ray diffraction (PXRD) and Fourier transform infrared (FTIR) spectroscopy. In addition, a supplied ZM (ZM-b) with a rod-like/wheatsheaf morphology was also analysed along with titanium dioxide (TiO₂). The simulants underwent thermal gravimetric analysis (TGA) and size analysis, where CPM was found to have a D50 value of 300 nm and a chemical formula of Cs₃PMo₁₂O₄₀·13H₂O, ZM-a a D50 value of 10 μm and a chemical formula of ZrMo₂O₇(OH)₂·3H₂O and ZM-b to have a D50 value of 14 μm and a chemical formula of ZrMo₂O₇(OH)₂·4H₂O. The synthesis of CPM was tracked via Ultraviolet-visible (UV-Vis) spectroscopy at both 25 °C and 50 °C, where the reaction was found to be first order with the rate constant highly temperature dependent. The morphology change from spheroidal CPM to cuboidal ZM-a was tracked via SEM, reporting to take 10 days. For the onward processing and immobilisation of these waste dispersions, centrifugal analysis was utilised to understand their settling behaviours, in both aqueous and 2 M nitric acid environments (mimicking current storage conditions). Spheroidal CPM was present in both conditions as agglomerated clusters, with relatively high settling rates. Conversely, the ZM were found to be stable in water, where their settling rate exponents were related to the morphology. In acid, the high effective electrolyte resulted in agglomeration and faster sedimentation.

Preparation and characterization of iron(III) 99Mo-molybdate(VI) gels for the assessment of 99mTc elution performance

New iron(III) 99Mo-molybdate(VI) gels (Fe99Mo) of high Mo content were prepared by the precipitation/filtration method. 99Mo–MoO3 dissolved in NaOH was added to aqueous solutions of Fe(NO3)3 at Mo/Fe mole fractions ~2.21 and 1.99 with continuous stirring at ambient room temperature. Two different Fe99Mo were precipitated from the mixed solutions adjusted at pH 2 and 4.7. The amount of water of hydration increased with the increasing the gel settling time and pH of the mixed solution. The matrices were characterized by radiometric, XRD, SEM, XRF, FT-IR, TGA, and DTA measurements. Small chromatographic columns of 2.0 g Fe99Mo containing ≥800 mg Mo tagged with 740 MBq 99Mo were eluted with 5 mL saline solution. Highly reproducible 99mTc elution indices suitable for preparation of 99Mo/99mTc generators were achieved from generator supported with 0.5 g Al2O3 filter. Elution performance of 99mTc radionuclide was highly dependent on the gel structural properties.

Synthesis of alumina 99Mo-molybdate(VI) gel matrices and evaluation of 99mTc elution performance

Synthesis of a novel alumina 99Mo-molybdate(VI) gel matrix of high Mo(VI) content and reproducible separation indices of the generated 99mTc radionuclde are described and briefly discussed. Similar mixture solutes of aluminate and low specific activity 99Mo-molybdate(VI) anions in concentrated NaOH are prepared. Then, the solutes are acidified with concentrated HCl, HNO3 and/or H2SO4 at pH 9.5–4.5. Physico-chemical investigations indicate that molybdate(VI) anions are strongly adsorbed onto in situ-precipitated pseudoboehmite from acidic solutions than from basic solutions. The maximum adsorption % of 99Mo (167 mg Mo/g matrix dried at 50 ℃) is achieved from the nitrate solution at pH 5.5. Separation of 99mTc from the corresponding gel matrix with physiological saline solution exhibits high elution yield with a narrow elution profile and radionuclidic, radiochemical and chemical purity indices comparable with 99mTc eluates from 99Mo/99mTc generators prepared by loading alumina with fission 99Mo.

TcGenerator Development: Up-to-DateTcRecovery Technologies for Increasing the Effectiveness ofMoUtilisation

A review on theMosources available today and on theTcgenerators developed up to date for increasing the effectiveness ofMoutilisation is performed in the format of detailed description of the features and technical performance of the technological groups of theMoproduction andTcrecovery. The latest results of the endeavour in this field are also surveyed in regard of the technical solution for overcoming the shortage ofMosupply. The technological topics are grouped and discussed in a way to reflect the similarity in the technological process of each group. The following groups are included in this review which are high specific activityMo: the current issues of production, the efforts of more effective utilisation, and the high specific activityMo-basedTcgenerator andTcconcentration units; low specific activityMo: theMoproduction based on neutron capture and accelerators and the direct production ofTcand the methods of increasing the specific activity ofMousing Szilard-Chalmers reaction and high electric power isotopic separator; up-to-date technologies ofTcrecovery from low specific activityMo: the solvent extraction-basedTcgenerator, the sublimation methods forMo/Tcseparation, the electrochemical method forTcrecovery, and the column chromatographic methods forTcrecovery. Besides the traditionalTc-generator systems, the integratedTcgenerator systems (Tcgenerator column combined with postelution purification/concentration unit) are discussed with the format of process diagram and picture of real generator systems. These systems are the technetium selective sorbent column-based generators, the high Mo-loading capacity column-based integratedTcgenerator systems which include the saline-eluted generator systems, and the nonsaline aqueous and organic solvent eluent-eluted generator systems using high Mo-loading capacity molybdategel and recently developed sorbent columns.Tcconcentration methods used in theTcrecovery from low specific activityMoare also discussed with detailed process diagrams which are surveyed in two groups forTcconcentration from the saline and nonsalineTc-eluates. The evaluation methods for the performance ofTc-recovery/concentration process and for theTc-elution capability versus Mo-loading capacity of generator column produced using low specific activityMosource are briefly reported. Together with the theoretical aspects ofTc/Moand sorbent chemistry, these evaluation/assessment processes will be useful for any further development in the field of theTcrecovery andMo/Tcgenerator production.

Indigenous technology development and standardization of the process for obtaining ready to use sterile sodium pertechnetate-Tc-99m solution from Geltech generator

Purpose of the Study:

The indigenous design and technology development for processing large scale zirconium molybdate-Mo-99 (ZrMo-99) Geltech generator was successfully commissioned in Board of Radiation and Isotope Technology (BRIT), India, in 2006. The generator production facility comprises of four shielded plant facilities equipped with tongs and special process gadgets amenable for remote operations for radiochemical processing of ZrMo-99 gel.

Results:

Over 2800 Geltech generators have been processed and supplied to user hospitals during the period 2006-2013. Geltech generator supplied by BRIT was initially not sterile. Simple elution of Tc-99m is performed by a sterile evacuated vial with sterile and pyrogen free 0.9% NaCl solution to obtain sodium (Tc-99m) pertechnetate solution. A special type online 0.22 μm membrane filter has been identified and adapted in Geltech generator.

Conclusions:

The online filtration of Tc-99m from Geltech generator; thus, provided sterile Tc-99m sodium pertechnetate solution. Generators assembled with modified filter assembly were supplied to local hospital in Mumbai Radiation Medicine Centre (RMC) and S.G.S. Medical College and KEM Hospital) and excellent performances were reported by users.

Separation of pertechnetate from molybdate by anion-exchange chromatography: Recovery of99mTc from (n, γ)99Mo and suitability for use in central radiopharmacy (CRPh)

A novel method for the recovery of99mTcO4−from (n, γ)99Mo using conventional anion-exchange chromatography over Dowex-1 × 8 column, followed by elution and subsequent novel purification over AgCl-alumina column is reported.99MoO42−solution (7 − 14 GBq/mg) in NaOH was passed down a Dowex-1 × 8 column (6 − 7 × 2 mm), collected and preserved for reuse on the subsequent days.99mTcO4−preferentially retained on the Dowex-1 column, was recovered quantitatively by elution with 4 ml of 4 M HNO3or 4 ml 0.2 M HClO4or 6 ml of 0.2 M NaI solution. Further purification to deliver99mTcO4−in a physiological vehicle has been achieved. Use of NaI eluent and post elution purification over a bed of 1 g AgCl + 1 g alumina developed has been adapted in preference to the other two eluents. The overall yield of99mTcO4−was 75%−85% and the quality features of99mTcO4−were compatible to radiopharmaceutical use. The method has applicability for decontamination of99gTc from spent99Mo waste solution and recovery of99gTc for research use. The procedure should also be equally applicable for recovery of188ReO4−from188WO42−in a radioisotope laboratory.

99mTc gel generators based on zirconium molybdate-99Mo: III: Influence of preparatory conditions of zirconium molybdate-99Mo gel on generator performance

The effect of subtle variations on zirconium molybdate-99Mo gel preparatory conditions, such as stoichiometry of reactants, pH of gel formation, conditioning of gel granulesetc., prior to elution were investigated primarily to arrive at the conditions resulting in high99mTc release and minimal99Mo breakthrough upon elution with normal saline. Zirconium molybdate-99Mo gels were prepared by reacting solutions of Zr and Mo in mole ratios of 0.75-1.5. Both water and normal saline were used for gel disintegration, and the release of99mTc and99Mo from gel columns into eluates was compared. Sharper elution profile of99mTc, but with significantly higher99Mo breakthrough (5-8 times), was obtained when water alone was used for disintegration and elution, in comparison to when saline was used.

Gels exhibiting optimum characteristics were found to be formed at a pH of 4-5 by reacting [Zr]:[Mo] in the mole ratio of 1.25:1 and after drying, the product was dispersed into granules by disintegration with normal saline.99mTc elution efficiency was found to be ∼75% and99Mo breakthrough ∼0.05%. The elution profile was sharp when a 6 g gel column coupled to a 2 g acidic alumina column (to trap99Mo) was eluted with 6-9 ml normal saline. Generators containing upto 23 GBq99Mo were prepared, eluted extensively without changing the alumina column and found to provide pertechnetate of good quality, commensurate with hospital radiopharmacy requirements.

High radioactive concentration of 99mTc from a zirconium [99Mo]molybdate gel generator using an acidic alumina column for purification and concentration

BACKGROUND

Newer applications of radiopharmaceuticals in nuclear medicine require pertechnetate of moderate to high radioactive concentration. Hence there is a need to develop simple procedures for the concentration of pertechnetate, and such a procedure is given in this paper.

METHODS

Ten to 20 ml of sodium [Tc]pertechnetate eluted in de-ionized water from a zirconium [Mo]molybdate (ZrMo) gel column generator was passed through 2 g of an acidic alumina bed (35 x 8 mm) in order to remove the co-eluted traces of Mo and to retain the pertechnetate. The retained pertechnetate was then re-eluted, quantitatively, in 3 ml of normal saline, from the alumina column.

RESULTS

About a 4-fold increase in radioactive concentration of Tc was obtained (cf. approximately 10-12 ml normal saline is required for the elution of Tc from the gel column). Generators containing up to 22.2 GBq (600 mCi) Mo in 6-7 g ZrMo gel column (35 x 13 mm) were prepared and a radioactive concentration of Tc up to 4 GBq x ml (110 mCi x ml) was obtained on the first day of use. The overall recovery of Tc was >90%, Mo breakthrough was 10 to 10% and the duration of concentration was 3-5 min. The chemical impurity in terms of Al, Mo and Zr was <10 ppm each. The same procedure for the concentration of pertechnetate was applied to generators with 12-15 g ZrMo gel beds to obtain a higher capacity Tc gel generator, with similar findings.

Effect of Zr:Mo ratio on 99mTc generator performance based on zirconium molybdate gels

Zirconium molybdate gels have shown to be viable alternatives for preparation of 99mTc generators using 99Mo produced by neutron activation. The aim of this work was to investigate the effect of the Zr:Mo molar ratio on the gel chemical structure and correlate it with the elution efficiency. A series of gels were prepared at Zr:Mo molar ratios from 0.5:1 to 2.3:1 and characterized by TGA, IR, XRD and UV. It was found that the variation of Zr:Mo ratio produces different polymolybdate arrangements on the octahedral units around to the zirconia which is mainly influenced by the water content. When the matrix molybdenum concentration was increased a lesser amount of water was found and the elution efficiencies were increased. However high elution efficiencies produce higher 99Mo breakthrough values. The gel formulation appears thus to be a compromise between the elution efficiency and the molybdenum breakthrough. The chemical-physical properties of these gels are presented and discussed.

A novel 99mTc delivery system using (n,gamma)99Mo adsorbed on a large alumina column in tandem with Dowex-1 and AgCl columns

99Mo of specific activity 7.4-14.8GBq (200-400mCi)/g was adsorbed on a 'jumbo' alumina column (40g, 90mm(H) x 20mm (dia.); 50g, 65mm(H) x 35mm(dia.). [99mTc]TcO4-, eluted with 50-70ml normal saline and applied to a tiny column of a strong anion exchanger, Dowex-1 x 8, 10-15 mg, 8-12 mm(H) x 1 mm(dia.). Pertechnetate was eluted from the Dowex-1 column with 5-6 ml of 0.2M Nal followed by washing with 1.5-1.8 ml water. Iodide was removed from this eluate by passage through a 1 g AgCl column (12 mm (H) x 8 mm (dia.)). The final product, pertechnetate, was recovered in 6.5-7.8 ml, while the NaCl content was close to that of normal saline. Each elution operation was complete in approximately 45 min. The mean practical yield was approximately 86% (n = 5). Closed cycle operation with sterile connecting tubes and multi-way stop-cocks was practised. The quality of the [99mTc]NaTcO4 thus obtained complies with the specifications applicable for radiopharmaceutical use. The major merit over other post-elution concentration methods is that the new procedure can function nearly independently of the volume of the primary eluate (in normal saline) from the alumina column generator (ACG). 99mTc generators containing as much as 80-100 g alumina for holding 14.8-18.5GBq (400-500 mCi) 99Mo (at the reference time) are feasible using approximately 15 mg Dowex-1 bed mass. A relatively user-friendly--cum--producer-friendly 99mTc generator system has been demonstrated making use of the inexpensive and easy to prepare (n,gamma)99Mo. The method is also applicable for the more costly 188W-188Re generator.

Post-elution concentration of 99TcmO4- by a single anion exchanger column: II. Preparation and evaluation of jumbo alumina column chromatographic generator for 99Tcm

We report on the preparation and evaluation of a large size (jumbo) alumina column (approximately 40 g, 90 x 20 mm) chromatographic generator and post-elution concentration of 99Tcm using a single column of a weak anion exchanger. The generator was eluted with approximately 40 ml of a modified single salt buffer solution of 1:1 v/v 0.025 M or 0.05 M NH4OAc:0.7 M AcOH. This eluate was then passed through a small column of DEAE cellulose, a common weak anion exchanger, to trap 99TcmO4-, which was recovered by elution in 6 ml of normal saline. This amounts to a 5- to 7-fold increase in radioactive concentration (RAC) of 99Tcm, when compared to the RAC on direct elution with normal saline from the same jumbo alumina column generator. The overall yield of 99Tcm was in the range of 70-90%. 99Mo breakthrough was 10(-3)-10(-4)%, radiochemical purity was > 98%, and chemical purity, in terms of Al and Mo content, < 10 ppm each. The compatibility of pertechnetate obtained by this method for preparing 99Tcm labelled formulations such as Tc-MDP and 99Tcm-ethyl cysteinate dimer was found to be satisfactory. These promising results open up the feasibility of using (n, gamma) 99Mo adsorbed on a large (40-60 g) alumina column as a relatively more user-friendly source of 99Tcm in comparison to methyl ethyl ketone extraction, and as a producer-friendly process in comparison to the zirconium molybdate gel method.

Zirconium molybdate gel as a generator for technetium-99m--II. High activity generators

The characteristics of zirconium molybdate gels were described in Part I of this paper. Here it is shown that zirconium molybdate gel, prepared from neutron irradiated molybdenum oxide with 99Mo specific activities between 4.3 and 13.5 GBq g-1 is sufficiently stable for use as a matrix in preparation of high activity 99mTc generators. Elution efficiencies of generators containing from 2 to 6 g of gel ranged from 83 to 50% for 10 mL elutions. Generators containing 150 g of gel were eluted with efficiencies of 80-98%, with the activity peak in the first 50 mL. Radionuclidic impurities were considerably below the limits set by the British Pharmacopoeia. Although the pH of eluates was less than 4, subsequent treatment with a small zirconium oxide bed provided adjustment to within BP limits, and reduced 99Mo impurity levels tenfold to values near 10(-4)%. No significant differences were found between the biodistributions in rats of radiopharmaceuticals prepared with pertechnetate from gel generators and those from other generators.