Reactor-produced radioisotopes from ORNL for bone pain palliation

An investigation of effects of level density models and gamma ray strength functions on cross-section calculations for the production of 90Y, 153Sm, 169Er, 177Lu and 186Re therapeutic radioisotopes via (n,γ) reactions

One of the methods used to treat different cancer diseases is the employment of therapeutic radioisotopes. Therefore, many clinical, theoretical and experimental studies are being carried out on those radioisotopes. In this study, the effects of level density models and gamma ray strength functions on the theoretical production cross-section calculations for the therapeutic radioisotopes 90Y, 153Sm, 169Er, 177Lu and 186Re in the (n,γ) route have been investigated. TALYS 1.9 code has been used by employing different level density models and gamma ray strength functions. The theoretically obtained data were compared with the experimental data taken from the literature. The results are presented graphically for better interpretation.

Opportunities and challenges for metal chemistry in molecular imaging: from gamma camera imaging to PET and multimodality imaging

The development of medical imaging is a highly multidisciplinary endeavor requiring the close cooperation of clinicians, physicists, engineers, biologists and chemists to identify capabilities, conceive challenges and solutions and apply them in the clinic. The chemistry described in this article illustrates how synergistic advances in these areas drive the technology and its applications forward, with each discipline producing innovations that in turn drive innovations in the others. The main thread running through the article is the shift from single photon radionuclide imaging towards PET, and in turn the emerging shift from PET/CT towards PET/MRI and further, combination of these with optical imaging. Chemistry to support these transitions is exemplified by building on a summary of the status quo, and recent developments, in technetium-99m chemistry for SPECT imaging, followed by a report of recent developments to support clinical application of short lived (Ga-68) and long-lived (Zr-89) positron emitting isotopes, copper isotopes for PET imaging, and combined modality imaging agents based on radiolabelled iron oxide based nanoparticles.

Therapeutic radionuclides in nuclear medicine: current and future prospects

The potential use of radionuclides in therapy has been recognized for many decades. A number of radionuclides, such as iodine-131 ((131)I), phosphorous-32 ((32)P), strontium-90 ((90)Sr), and yttrium-90 ((90)Y), have been used successfully for the treatment of many benign and malignant disorders. Recently, the rapid growth of this branch of nuclear medicine has been stimulated by the introduction of a number of new radionuclides and radiopharmaceuticals for the treatment of metastatic bone pain and neuroendocrine and other malignant or non-malignant tumours. Today, the field of radionuclide therapy is enjoying an exciting phase and is poised for greater growth and development in the coming years. For example, in Asia, the high prevalence of thyroid and liver diseases has prompted many novel developments and clinical trials using targeted radionuclide therapy. This paper reviews the characteristics and clinical applications of the commonly available therapeutic radionuclides, as well as the problems and issues involved in translating novel radionuclides into clinical therapies.

Cross section measurements of deuteron induced nuclear reactions on natural tungsten up to 34 MeV

(186g)Re is a β-/γ emitter of great interest for nuclear medicine. It has shown successful results on bone metastases palliation and has similar chemical properties as (99m)Tc, the most commonly used imaging agent. (186g)Re is routinely produced using rhenium target in nuclear reactor. Higher specific activity could be obtained using accelerators. In this paper, production cross section values are presented for the (nat)W(d,x)(186g)Re reaction up to 34MeV, using the stacked-foils method and gamma spectrometry. From this data set, the thick target production yield of (186g)Re is determined and compared with the validated values of the IAEA and also with the proton route. The production cross sections of the (nat)W(d,x)(183,182g,184m,184g,181)Re and (nat)W(d,x)(187)W reactions have also been determined. A good agreement is found with the literature. Our data are compared with the version 1.6 (December 2013) of the TALYS code which shows discrepancies both on the shape and on the amplitude for these deuteron induced reactions.

Palliation and survival after repeated (188)Re-HEDP therapy of hormone-refractory bone metastases of prostate cancer: a retrospective analysis

This retrospective study compared the effects of single and multiple administrations of (186)Re-hydroxyethylidenediphosphonate ((186)Re-HEDP) on palliation and survival of prostate cancer patients presenting with more than 5 skeletal metastases.

METHODS

A total of 60 patients were divided into 3 groups. Group A (n = 19) consisted of patients who had received a single injection; group B (n = 19), patients who had 2 injections; and group C (n = 22), patients who had 3 or more successive injections. The (188)Re-HEDP was prepared using non-carrier-added (188)Re obtained from an in-house (188)W/(188)Re generator after dilution with carrier perrhenate. Patients' data available from the referring physicians-including prostate-specific antigen levels-were entered into a Windows-based matrix and analyzed using a statistical program. The Gleason scores were similar for all 3 groups.

RESULTS

Mean survival from the start of treatment was 4.50 ± 0.81 mo (95% confidence interval [CI], 2.92-6.08) for group A, 9.98 ± 2.21 mo (95% CI, 5.65-14.31) for group B, and 15.66 ± 3.23 (95% CI, 9.33-22.0) for group C. Although the 3 groups did not differ in Gleason score, the number of lost life-years was significantly lower in group C than in groups A and B. Pain palliation was achieved in 89.5% of group A, 94.7% of group B, and 90.9% of group C.

CONCLUSION

Posttreatment overall survival could be improved from 4.50 to 15.66 mo by multiple-injection bone-targeted therapy with (188)Re-HEDP, when compared with a single injection. Significant pain palliation was common and independent of administration frequency.

The role of coordination chemistry in the development of copper and rhenium radiopharmaceuticals

There are several isotopes of copper and rhenium that are of interest in the development of new molecular imaging or radiotherapeutic agents. This perspective article highlights the role of coordination chemistry in the design of copper and rhenium radiopharmaceuticals engineered to selectively target tissue of interest such as cancer cells or pathological features associated with Alzheimer's disease. The coordination chemistry of copper bis(thiosemicarbazone) derivatives and copper macrocyclic complexes is discussed in terms of their potential application as targeted positron emission tomography tracers for non-invasive diagnostic imaging. A range of rhenium complexes with different ligands with rhenium in different oxidation states are introduced and their potential to be translated to new radiotherapeutic agents discussed.

Multispecies animal investigation on biodistribution, pharmacokinetics and toxicity of 177Lu-EDTMP, a potential bone pain palliation agent

INTRODUCTION

Radionuclide therapy (RNT) is an effective method for bone pain palliation in patients suffering from bone metastasis. Due to the long half-life, easy production and relatively low beta- energy, (177)Lu [T(1/2)=6.73 days, E(beta max)=497 keV, E(gamma)=113 keV (6.4%), 208 keV (11%)]-based radiopharmaceuticals offer logistical advantage for wider use. This paper reports the results of a multispecies biodistribution and toxicity studies of (177)Lu-EDTMP to collect preclinical data for starting human clinical trials.

METHODS

(177)Lu-EDTMP with radiochemical purity greater than 99% was formulated by using a lyophilized kit of EDTMP (35 mg of EDTMP, 5.72 g of CaO and 14.1 mg of NaOH). Biodistribution studies were conducted in mice and rabbits. Small animal imaging was performed using NanoSPECT/CT (Mediso, Ltd., Hungary) and digital autoradiography. Gamma camera imaging was done in rabbits and dogs. Four levels of activity (9.25 through 37 MBq/kg body weight) of (177)Lu-EDTMP were injected in four groups of three dogs each to study the toxicological effects.

RESULTS

(177)Lu-EDTMP accumulated almost exclusively in the skeletal system (peak ca. 41% of the injected activity in bone with terminal elimination half-life of 2130 and 1870 h in mice and rabbits, respectively) with a peak uptake during 1-3 h. Excretion of the radiopharmaceutical was through the urinary system. Imaging studies showed that all species (mouse, rat, rabbit and dog) take up the compound in regions of remodeling bone, while kidney retention is not visible after 1 day postinjection (pi). In dogs, the highest applied activity (37 MBq/kg body weight) led to a moderate decrease in platelet concentration (mean, 160 g/L) at 1 week pi with no toxicity.

CONCLUSION

The protracted effective half-life of (177)Lu-EDTMP in bone supports that modifying the EDTMP molecule by introducing (177)Lu does not alter its biological behaviour as a specific bone-seeking tracer. Species-specific pharmacokinetic behavior differences were observed. Toxicity studies in dogs did not show any biological adverse effects. The studies demonstrate that (177)Lu-EDTMP is a promising radiopharmaceutical that can be further evaluated for establishing as a radiopharmaceutical for human use.

Complexation of 188Re-phosphonates: in vitro and in vivo studies

MDP (methylenediphosphonate) and HEDP (hydroxyethylidene diphosphonate), both diphosphonates, and EDTMP (ethylenediamine tetramethylene phosphonic acid), a tetraphosphonate ligand, have been previously labeled with 188Re for use in metastatic bone-pain palliation. The aim of this study was a comparison between the three complexes 188Re-MDP, 188Re-HEDP and 188Re-EDTMP concerning the complexation conditions, in order to achieve maximum yield, stability and bone uptake. Methods: MDP was dissolved in water and HEDP and EDTMP were dissolved in NaOH 1N followed by reduction of pH with HCl 1N. To all mixtures stannous chloride and 188Re4 - were added in a nitrogen atmosphere. The preparations were heated in boiling water bath for 15min. Yield as well as radiochemical stability was estimated by ITLC. Different concentrations of phosphonates and stannous chloride were evaluated. Biodistribution studies in Swiss mice were done for the three 188Re-phosphonates that presented the best radiochemical yield. The optimal ligand concentration for maximum complexation was 85.2mM for MDP, 72.8mM for HEDP and 45.8mM for EDTMP. The best amount of SnCl2·2H2O} was 1.5mg/mL for 188Re-HEDP and 1mg/mL for both 188Re-MDP and 188Re-EDTMP. In these conditons the three complexes showed a complexation rate above 95. Reasonable radiochemical stability for 24 hours was achieved by 188Re-EDTMP when employing ascorbic acid. All products showed a great uptake by the kidneys. 188Re-EDTMP had the greatest uptake by femur (3.1±0.2 ID/g) followed by 188Re-MDP (1.2±0.1 ID/g) and 188Re-HEDP (1.0±0.1 ID/g), 4 hours post injection. 188Re-EDTMP displayed a femur bone/muscle ratio of 28.5, 188Re-MDP 4.9 and 188Re-HEDP 4.9. In conclusion 188Re-EDTMP demonstrated the best potential as a radiopharmaceutical for bone cancer pain relief, encouraging further dosimetric studies and clinical trials.

Therapeutic radionuclides and nuclear data

The nuclear data required for the production and endotherapeutic application of radionuclides are outlined. The three types of therapeutic radionuclides, viz. β--emitters, α-emitters and Auger electron emitters, are considered and the role of some β+-emitters in therapy planning is discussed. The status of available data is reviewed.

Development of a high performance (188)W/(188)Re generator by using a synthetic alumina

A synthetic alumina functionalized with a sulfate moiety has been developed as the column material of (99)Mo/(99m)Tc and (188)W/(188)Re generators. This material is synthesized by a sol-gel processing. In order to characterize the adsorbent for the (188)W/(188)Re separation, both batch and column contact experiments were conducted. As a result of the experiments, it is found that the maximum capacity of the adsorbent for tungsten is higher than 450mg/g. Hence it is possible to produce approximately 3Ci (188)W/(188)Re generator with only 1g of the adsorbent from (188)W solutions supplied from ORNL, USA or RIAR, Russia. A demonstration study was conducted to show the performance of an (188)W/(188)Re generator column. In this study, 1Ci of (188)W purchased from RIAR, Russia, is loaded on a 0.9cm ID column packed with 0.7g of the adsorbent. Elution of (188)Re is performed every 4-7 days by using the saline solution for more than three months. Nearly 100% of tungsten is loaded by passing 5ml of the (188)W solution (pH=8) through the dry packed column at a 1ml/min flow rate. Elution efficiency of (188)Re is 70-90% by using 5ml of the saline solution. The ratio of (188)W/(188)Re in the eluted solution is 0.002-0.003%. When a Sep-Pak containing 0.26g of acid alumina is installed as a tandem column, the ratio is decreased to less than 10(-3)%. Thin layer chromatography for the eluted (188)Re solution shows 100% radiochemical purity. Also, alumina content in the eluted solution shows less than 10ppm. Through this study, the performance of this adsorbent was successfully demonstrated. By using the developed adsorbent, minimization of the generator column and consequently the volume of eluant could be possible while maintaining the quality of (188)Re just as much as that available in the market.

Bifunctional coupling agents for radiolabeling of biomolecules and target-specific delivery of metallic radionuclides

Receptor-based radiopharmaceuticals are of great current interest in molecular imaging and radiotherapy of cancers, and provide a unique tool for target-specific delivery of radionuclides to the diseased tissues. In general, a target-specific radiopharmaceutical can be divided into four parts: targeting biomolecule (BM), pharmacokinetic modifying (PKM) linker, bifunctional coupling or chelating agent (BFC), and radionuclide. The targeting biomolecule serves as a "carrier" for specific delivery of the radionuclide. PKM linkers are used to modify radiotracer excretion kinetics. BFC is needed for radiolabeling of biomolecules with a metallic radionuclide. Different radiometals have significant difference in their coordination chemistry, and require BFCs with different donor atoms and chelator frameworks. Since the radiometal chelate can have a significant impact on physical and biological properties of the target-specific radiopharmaceutical, its excretion kinetics can be altered by modifying the coordination environment with various chelators or coligand, if needed. This review will focus on the design of BFCs and their coordination chemistry with technetium, copper, gallium, indium, yttrium and lanthanide radiometals.

177Lu-EDTMP: a viable bone pain palliative in skeletal metastasis

Designing ideal radiopharmaceuticals for use as bone pain palliatives require the use of a moderate energy beta() emitter as a radionuclide and a suitable polyaminophosphonic acid as a carrier molecule. Owing to its suitable decay characteristics [T(1/2) = 6.73 d, E((max)) = 497 keV, E() = 113 keV (6.4%), 208 keV (11%)] as well as the feasibility of large-scale production in adequate specific activity and radionuclidic purity using a moderate flux reactor, 177Lu could be considered as a promising radionuclide for palliative care in painful bone metastasis. The present study was therefore, oriented toward the preparation and biologic evaluation of 177Lu complex of ethylenediaminetetramethylene phosphonic acid (EDTMP) in various animal models, with an aim to prepare a viable radiopharmaceutical for bone pain palliation. 177Lu was produced with a specific activity of approximately 12 GBq/mg (approximately 324 mCi/mg) and radionuclidic purity of 99.98% by irradiation of natural Lu2O3 targeted at a thermal neutron flux of approximately 6 x 10(13) n/cm(2).s for 21 days. 177Lu-EDTMP complex was prepared in high-yield and excellent radiochemical purity (>99%), using EDTMP synthesized and characterized in-house. The complex exhibited excellent in vitro stability at room temperature. Biodistribution studies in Wistar rats showed a rapid skeletal accumulation of injected activity [(1.74 +/- 0.30)% per gram in femur at 3 hours postinjection] with a fast clearance from blood and minimal uptake in any of the major organs. Scintigraphic imaging studies carried out in normal Wistar rats, New Zealand white rabbits, as well as in Beagle dogs also demonstrated significant accumulation of the agent in the skeleton and almost no retention of activity in any other vital organs.

Characterization of Re-188–Sn microparticles used for synovitis treatment

Rhenium-188 labeled tin (Sn) microparticles were developed for pain palliation therapy in the patients suffering from synovitis with acute pain. The rhenium tin microparticles were prepared using stannous chloride and freshly eluted (188)ReO(4)(-) from (188)W/(188)Re generator. The aggregated colloidal particles, packed in a spherical form after boiling for 90-120min were analyzed using electron microscope. The size, surface morphology and stability of microparticles were analyzed by changing temperature and volume conditions. The small colloidal particles clustered and formed spherical microparticles. The 90% of microparticles were in 5-10microm range, after 90min and 120min of boiling. The radiolabeling efficiency was improved to 98% after centrifugation for 10min at 3500rpm. The formulations were stable but the increase in volume had inverse effect on labeling efficiency. No leak was observed from knee area up to 24h with 15-20mCi injection of (188)Re-Sn microparticles. The relief in treated patients, from the pain and inflammation, was observed clinically and by (99m)Tc-MDP perfusion scan.

Development of semi-automated system for preparation of (188)Re aqueous solutions of high and reproducible activity concentrations

A semi-automated system has been developed for elution and concentration of the (188)Re-eluate from 111 GBq (3 Ci) (188)W/(188)Re-generators to provide a dissolved beta-source of high (188)Re-activity per unit volume. The elution progress and concentration were precisely and continuously monitored by use of collimated diode detectors. By using ion exchange cartridges, small eluate volumes (2-3 ml) of maximum 40 GBq, (188)Re/ml activity concentration were routinely prepared. The concentrated (188)Re solutions were used to beta-irradiate aqueous suspensions and solutions of iodine species to evaluate a simulation of the extent of radiolytic decomposition of chemical species (AgI and CH(3)I) expected to accumulate in the containment sump of a nuclear reactor in the event of a severe accident with reproducible dose rates of up to 0.4 Gys(-1). Results have shown that AgI colloidal particles decompose to varying extents, depending on conditions, and in proportion to their initial mass, which indicates surface oxidation. Experiments have also confirmed CH(3)I decomposition in proportion to initial aqueous concentration.

Syntheses and reactivity of 'sulfur rich' Re(iii) and Tc(iii) complexes containing trithioperoxybenzoate, dithiobenzoate and dithiocarbamate ligands

Reduction-substitution reactions of [M(O)Cl(4)](-)(M=Re, (99)Tc) precursors with an excess of substituted dithiobenzoate ligands (R-PhCS(2))(-) in dichloromethane/methanol mixtures afford a series of six-coordinated neutral mixed-ligand complexes of the type M(III)(R-PhCS(3))(2)(R-PhCS(2))(M=Re; Rel--9; M=99)Tc; Tel--9). The coordination sphere is entirely filled by sulfur donor atoms, and the complexes adopt a distorted trigonal prismatic arrangement, as assessed by the X-ray crystal structure analysis of Re(4-Me-PhCS(3))(2)(4-Me-PhCS(2)), Re 2. These compounds show sharp proton and carbon NMR profiles, in agreement with the diamagnetism typical of low spin d(4) trigonal prismatic configurations. The red-ox processes involve reduction of the metal from Re(v) to Re(iii) and oxidation of dithiobenzoate to trithioperoxybenzoate. M2--9 complexes contain a substitution-inert [M(R-PhCS(3))(2)](+) moiety including the metal and two trithioperoxybenzoate fragments, while the third dithiobenzoate ligand is labile. The latter is efficiently replaced by reaction with better nucleophiles such as diethyldithiocarbamate giving a further class of mixed ligand complexes of the type M(III)(R-PhCS(3))(2)(Et(2)NCS(2))(M=Re; Re 10--18; M=(99)Tc; Tc--18), which retain the trigonal prismatic arrangement, as determined by the X-ray analyses of the representative compounds Re(PhCS(3))(2)(Et(2)NCS(2)), Re 10 and (99)Tc(PhCS(3))(2)(Et(2)NCS(2)), Tc 10.

Effects of dose, intervention time, and radionuclide on sodium iodide symporter (NIS)-targeted radionuclide therapy

The sodium iodide symporter (NIS) mediates iodide uptake into thyrocytes and is the molecular basis of thyroid radioiodine therapy. We previously have shown that NIS gene transfer into the F98 rat gliomas facilitated tumor imaging and increased survival by radioiodine. In this study, we show that: (1) the therapeutic effectiveness of (131)I in prolonging the survival time of rats bearing F98/hNIS gliomas is dose- and treatment-time-dependent; (2) the number of remaining NIS-expressing tumor cells decreased greatly in RG2/hNIS gliomas post (131)I treatment and was inversely related to survival time; (3) 8 mCi each of (125)I/(131)I is as effective as 16 mCi (131)I alone, despite a smaller tumor absorbed dose; (4) (188)ReO(4), a potent beta(-) emitter, is more efficient than (131)I to enhance the survival of rats bearing F98/hNIS gliomas. These studies demonstrate the importance of radiopharmaceutical selection, dose, and timing of treatment to optimize the therapeutic effectiveness of NIS-targeted radionuclide therapy following gene transfer into gliomas.

Repeated bone-targeted therapy for hormone-refractory prostate carcinoma: tandomized phase II trial with the new, high-energy radiopharmaceutical rhenium-188 hydroxyethylidenediphosphonate

PURPOSE

We investigated the effect of repeated bone-targeted therapy with rhenium-188 hydroxyethylidenediphosphonate (HEDP) in patients with progressive, hormone-resistant prostate carcinoma and bone pain. The aim of this study was to determine the pain palliation and the antitumor effect of rhenium-188 HEDP treatments.

PATIENTS AND METHODS

Sixty-four patients were randomly assigned to one of two groups for radionuclide therapy with rhenium-188 HEDP; patients of group A received a single injection, patients of group B received two injections (interval, 8 weeks). After therapy, patients were followed-up by assessment of pain palliation and clinical outcome until death.

RESULTS

In both groups, toxicity was low, with moderate thrombopenia and leukopenia (maximum common toxicity criteria grade of 2). The effectiveness of rhenium-188 HEDP for pain palliation was better in the repeated treatment group (group B), with a response rate and time of response of 92% and 5.66 months, respectively (P =.006 and P =.001). In group B, 11 (39%) of 28 patients had a prostate-specific antigen decrease of more than 50% for at least 8 weeks, compared with two (7%) of 30 patients in the single-injection group (group A). The median times to progression of group A and group B were 2.3 months (range, 0 to 12.2 months) and 7.0 months (range, 0 to 24.1 months), respectively (P =.0013), and the median overall survival times were 7.0 months (range, 1.3 to 36.7 months) and 12.7 months (range, 4.1 to 32.2 months), respectively (P =.043).

CONCLUSION

Compared with single-injection therapy, repeated bone-targeted therapy with rhenium-188 HEDP administered to patients with advanced progressive hormone-refractory prostate carcinoma enhanced pain palliation and improved progression-free and overall survival. Larger studies are justified to further evaluate the use of rhenium-188 HEDP.

DA-7911, 188Rhenium-tin colloid, as a new therapeutic agent of rheumatoid arthritis

Radiation synovectomy is one of the most useful methods for treating patients with refractory synovitis because of its convenience, long-term effects, repeatability and the avoidance of surgery. In this study, we investigated the toxicity, stability and biodistribution of a rhenium-188 (188Re)-tin colloid to evaluate its suitability as a synovectomy agent. Twenty four hours after injecting the 188Re-tin colloids (74 KBq/0.1 mL) into the tail vein of ICR mice, most of the 188Retin colloidal particles was found in the lungs. In addition, there were no particle size changes at either room temperature or at 37 degrees C after injecting the 188Re-tin colloids in human plasma and synovial fluid. In vitro stability tests showed that the 188Re-tin colloid remained in a colloidal form without a critical size variation over a 2-day period. We investigated the leakage of 188Retin colloids from the intraarticular injection site with gamma counting in New Zealand white rabbits. The 188Re-tin colloids (55.5 MBq/0.15 mL) were injected at the cavum articular and the mean retention percentage of the 188Re-tin colloid was 98.7% for 1 day at the injection site, which suggests that there was neither change in the particle size nor leakage at the injection sites. In the biodistribution study with the SD rats, the liver showed the highest radioactivity (0.0427% ID/organ) except for the injected knees (99.49%). In the SD rats, mild toxicities including the skin or a synovium inflammation were observed as a result of a radioactivity of 15 mCi/kg at the intraarticular injection site. However, there was no systemic toxicity. In the Ovalbumin (OVA)-induced arthritic rabbits, the 188Re-tin colloid improved the macroscopic, the histological score and reduced the knee joint diameter when compared to the arthritic control. In conclusion, a 188Re-tin-colloid is considered as a strong candidate for radiation synovectomy with a superior efficacy and safety.

Physico-chemical characterisation and biological evaluation of 188-Rhenium colloids for radiosynovectomy

BACKGROUND: Radiosynovectomy is a type of radiotherapy used to relieve pain and inflammation from rheumatoid arthritis. In this study, 188-Rhenium (188Re) colloids were characterized by physical and biological methodologies. This was used to assess which parameters of the kit formulation would be the basis in the development of a more effective radiopharmaceutical for synovectomy. Intraarticular injection in knees of rabbits assessed cavity leakage of activity. METHODS: The physical characteristics of tin (Sn) and sulphur (S) colloids were determined to assess the formulation with suitable properties. Particles were grouped in three ranges for analyzing their distribution according to their number, volume and surface. The ideal particle size range was considered to be from 2 to 10 microns. Membrane filtration and laser diffraction characterization methodologies were used. RESULTS: While membrane filtration could give misleading data, laser diffraction proportions more reliable results. The Sn colloid showed a better distribution of particle volume and surface than S colloid, in the 2 to 10 microns range. The 188Re-Sn colloid was obtained with a radiochemical purity higher than 95% after 30 minutes of autoclaving. While Sn colloid kit stability was verified for 60 days, the 188Re-Sn preparation was stable in the first 24 hrs. No significant intrabatch variability (n = 3) was detected. Biodistribution and scintigraphic studies in rabbits after intraarticular injection showed relevant activity only in knee, being 90% at 48 hours. CONCLUSION: The 188Re-Sn colloid is easy to prepare, is stable for 24 hours and shows minimal cavity leakage after intraarticular injection into rabbit knees, suggesting this radiotherapeutical agent has suitable physical properties for evaluation for joint treatment in humans.

Labelling of Re-ABP with 188Re for bone pain palliation

Etidronate and medronate have been labelled with technetium-99m (99mTc-HEDP, 99mTc-MDP) for bone scanning and, with rhenium-188 (188Re-HEDP) to palliate the pain resulting from bone metastases. The objective of this study was to label alendronate, ABP, a new bisphosphonate, with SnF2-reduced-188Re. The reagents for the 5 mg ABP kit were SnF2, KReO4 and gentisic acid at acid pH. The chemical, spectroscopic and microscopic characteristics, quality control, rat bone uptake of [188Re]Re-ABP and similarities with 99mTc-ABP are presented. We conclude that this is a promising new radiopharmaceutical for bone metastases pain palliation.

Re-HEDP : pharmacokinetic characterization, clinical and dosimetric evaluation in osseous metastatic patients with two levels of radiopharmaceutical dose

BACKGROUND: A study for pain relief therapy with 188Re-HEDP was done in patients with bone metastases secondary to breast and prostate cancer. MATERIALS AND METHODS: Patients received 1.3 or 2.2 GBq, in single or multiple doses. Platelets, white and red cells were evaluated during 11 weeks. Pharmacokinetic characterization was done from blood and urine samples for 5 patients along 24 hours. Urinary excretion was evaluated in other 16 patients during 6 hours. Bone uptake was estimated as remaining activity in whole body. Scintigraphic images were acquired at 2 and 24 hs post-administration. Absorbed dose in bone marrow was estimated with Mirdose3. Analgesics intake and pain score were daily recorded. Tumour markers (PSA, and Tn-structure) were monitored in 9 patients during 4 to 6 months. Single doses of low activity (1.3 GBq) were given to twelve patients. Nine patients received multiple doses. RESULTS: All except one patient had normal levels of platelets, white and red cells. Remaining dose in blood at 2 hours was 9%. Urinary elimination was 58%. Bone uptake at 24 hours was 43% (mean value; n = 5). No changes of the haematological parameters were detected along follow-up period. Pain relief was evidenced by decrease or supression of opioid analgesic and by subjective index. PSA showed a decrease in prostate cancer patients (n = 4). Tn-structure showed a significant increase after 4 to 8 months. CONCLUSION: Single or multiple dose scheme could be safely used, with administered activity of 188Re-HEDP up to 60 mCi, with low bone marrow absorbed doses.

Studies on the preparation and stability of samarium-153 propylene diamine tetramethylene phosphonate (PDTMP) complex as a bone seeker

Propylene diamine tetra methylene phosphonate (PDTMP) was synthesised by modifying a method reported for the synthesis of EDTMP. Complexation of the synthesised phosphonate ligand with 153Sm was carried out by varying the experimental parameters and the complex was radiochemically characterized. Biodistribution studies showed that the uptake by bone in rats was 2% per g of bone, which was retained upto 48 h. The uptake by other organs was insignificant, except by the liver which showed a slightly higher absorption.

Preparation of (188Re) Re-AEDP and its biodistribution studies

The synthesis of the Re (V) complex and preparation of 188Re-AEDP are described using 188Re which was obtained from the alumina-based 188W/188Re generator. Dependence of the radiolabeling yields of 188Re-AEDP on reducing agent concentration, AEDP concentration, pH and addition of carrier was examined. In the case of optimum conditions, the radiolabeling yields of 188Re-AEDP were 92-93% for carrier-free 188Re and 95-98% for carrier-added 188Re. The stability of 188Re-AEDP at pH approximately 6 was studied and it is found that the carrier has a significant effect on the stability of 188Re-AEDP. The biodistribution of carrier-free and carrier-added 188Re-labelled compounds in rats was also measured. The results show that 188Re (carrier-added)-AEDP is a potential bone palliation radiopharmaceutical due to its high skeletal uptake, rapid blood clearance and relatively low soft tissue absorption.

Trithiacyclononane as a ligand for potential technetium and rhenium radiopharmaceuticals: synthesis of [M(9S3)(SC2H4SC2H4S)][BF4] (M = 99Tc, Re, 188Re) via C-S bond cleavage

Chemical or electrochemical reduction of the 1,4,7-trithiacyclononane (9S3) complexes [MII(9S3)2][BF4]2 (M = Re (3a) or Tc (3b)) results in instantaneous C-S bond cleavage to yield ethene and the stable MIII thiolate complexes [MIII(9S3)L][BF4] (M = Re (4a) or Tc (4b), L = SCH2CH2SCH2CH2S). Compounds 4 have been characterized by 1H NMR spectroscopy, and the pseudo-octahedral geometry of 4b has been confirmed by X-ray crystallography. Upon electrochemical reduction 4a loses ethene, while 4b can be reversibly reduced to [TcII(9S3)L], which is then further reduced to Tc(I) with loss of ethene. Successive ethene loss is observed in the mass spectra of compounds 3 and 4. The radiosynthesis of 4a with 188Re can be comfortably completed within 10 min starting with 188ReO4- from a 188W/188Re generator, with a radiochemical yield in excess of 90%, and thus represents a practical approach to the preparation of stable 188Re (and 99mTc) thioether complex derivatives/conjugates for clinical use. Crystal data: 4b, C10H20S6Tc, orthorhombic Pbca, a = 12.233(2) A, b = 14.341(2) A, c = 20.726(3) A, Z = 8.

Intravascular irradiation using Re-186 liquid-filled balloon catheters: correlation between experimental and theoretical studies

PURPOSE

Optimization of intravascular radiation to reduce stenosis following coronary angioplasty requires the ability to predict the patterns of radiation dose distribution. This investigation evaluated the agreement between Monte Carlo simulations and experimental radiation dose measurements for a radioisotope liquid-filled balloon catheter in a tissue equivalent phantom.

METHODS AND MATERIALS

Direct measurements of the radiation dose from Re-186 liquid-filled balloons were made using thermoluminescent dosimeters (TLDs) and radiochromic film. Monte Carlo simulations were carried out using the Monte Carlo N-Particle code system (MCNP4B).

RESULTS

The Monte Carlo generated dose values agreed with the experimentally determined results within the statistical uncertainty. A slightly higher penetration was indicated by regression analysis for the TLD data relative to the MCNP4B prediction that may be due to experimental configuration anomalies. For this balloon catheter, approximately 55 mCi of Re-186 will deliver 15 Gy at a 0.5 mm depth in tissue equivalent material in 5 min.

CONCLUSIONS

Correlation between experimentally measured dose values and Monte Carlo computation supports the position that MCNP4B simulations constitute a valuable tool for investigating various clinical therapy designs. The agreement between Monte Carlo calculations and experiments provide confidence in applying MCNP4B to more sophisticated geometries of interest, and other methods of intravascular radiation dose delivery.