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Capture Instead of Release: Defect-Modulated Radionuclide Leaching Kinetics in Metal–Organic Frameworks
Comparison of defect-controlled leaching-kinetics modulation of metal–organic frameworks (MOFs) and porous functionalized silica-based materials was performed on the example of a radionuclide and radionuclide surrogate for the first time, revealing an unprecedented readsorption phenomenon. On a series of zirconium-based MOFs as model systems, we demonstrated the ability to capture and retain >99% of the transuranic 241 Am radionuclide after 1 week of storage. Here, we report the possibility of tailoring radionuclide release kinetics in MOFs through framework defects as a function of postsynthetically installed organic ligands including cation-chelating crown ether-based linkers. Based on comprehensive analysis using spectroscopy (EXAFS, UV–vis, FTIR, and NMR), X-ray crystallography (single crystal and powder), and theoretical calculations (nine kinetics models and structure simulations), we demonstrated the synergy of radionuclide integration methods, topological restrictions, postsynthetic scaffold modification, and defect engineering. This combination is inaccessible in any other material and highlights the advantages of using well-defined frameworks for gaining fundamental knowledge necessary for the advancement of actinide-based material development, providing a pathway for addressing upcoming challenges in the nuclear waste administration sector.
“Boarding-Up”: Radiation Damage and Radionuclide Leaching Kinetics in Linker-Capped Metal–Organic Frameworks
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Allometric-kinetic model predictions of radionuclide dynamics across turtle taxa
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Leaching Model of Radionuclides in Metal-Organic Framework Particles
Metal-organic frameworks (MOFs) have been used to sequester radionuclides and seal them inside of porous scaffolds using postsynthetic modification procedures. Experiments show that certain Zr-MOF with different capping linkers significantly affects the radionuclide release kinetics. In this work, we developed a leaching model of radionuclides in Zr-MOF particles. The model assumes that uranyl species occupy two energetically favored sites: the metal node and the MOF pores. For a given overall concentration of uranyl species, the partitions of uranyl species at the metal nodes and within the pores are determined by their chemical potentials. The model also considers the effect of particle surface and concentration on chemical potentials and diffusivity. The effects of spatial and structural dependent chemical potentials and diffusivity as well as particle sizes on leaching kinetics are investigated with the model. Predicted and measured uranyl leaching kinetics in Zr-MOF particles under batch experiments are compared. The results demonstrate the model’s capability for exploring the mechanisms of leaching and provide guidance for material design.
Characteristics of metal waste forms containing technetium and uranium
2 prototype alloys: RAW-1(Tc) and RAW-2(UTc) suitable for a wide range of waste stream compositions are being evaluated to support development of a waste form degradation model that can be used to calculate radionuclide source terms for a range of waste form compositions and disposal environments. Tests and analyses to support formulation of waste forms and development of the degradation model include detailed characterizations of the constituent phases using SEM/EDS and TEM, electrochemical tests to quantify the oxidation behavior and kinetics of the individual and coupled phases under a wide range of environmental conditions, and corrosion tests to measure the gross release kinetics of radionuclides under aggressive test conditions.
Role of Mg{sup 2+}, Sr{sup 2+}, and F{sup –} ions in octacalcium phosphate crystallization
We have synthesized octacalcium phosphate (OCP) in the presence of inorganic additives (magnesium, strontium, and fluoride ions) and studied the composition, morphology, thermal stability, and dynamic dissolution of the samples thus obtained. It has been shown that, in addition to OCP, magnesium and strontium ions favor the formation of brushite and hydroxyapatite (HA), whereas fluoride ions favor the formation of HA and fluorohydroxyapatite (FHA). We have proposed a process for the preparation of powder materials whose resorption kinetics in corrosive liquid media are corrected by adding dopants capable of activating the dissolution process.
Muscle contraction increases carnitine uptake via translocation of OCTN2
Highlights: Black-Right-Pointing-Pointer Muscle contraction augmented carnitine uptake into rat hindlimb muscles. Black-Right-Pointing-Pointer An increase in carnitine uptake was due to an intrinsic clearance, not blood flow. Black-Right-Pointing-Pointer Histochemical analysis showed sarcolemmal OCTN2 was emphasized after contraction. Black-Right-Pointing-Pointer OCTN2 protein in sarcolemmal fraction was increased in contracting muscles. -- Abstract: Since carnitine plays an important role in fat oxidation, influx of carnitine could be crucial for muscle metabolism. OCTN2 (SLC22A5), a sodium-dependent solute carrier, is assumed to transport carnitine into skeletal muscle cells. Acute regulation of OCTN2 activity in rat hindlimb muscles was investigated in response to electrically induced contractile activity. The tissue uptake clearance (CL{sub uptake}) of L-[{sup 3}H]carnitine during muscle contraction was examined in vivo using integration plot analysis. The CL{sub uptake} of [{sup 14}C]iodoantipyrine (IAP) was also determined as an index of tissue blood flow. To test the hypothesis that increased carnitine uptake involves the translocation of OCTN2, contraction-induced alteration in the subcellular localization of OCTN2 was examined. The CL{sub uptake} of L-[{sup 3}H]carnitine in the contracting muscles increased 1.4-1.7-fold as compared to that in the contralateral resting muscles (p < 0.05). The CL{sub uptake} of [{sup 14}C]IAP was much higher than that of L-[{sup 3}H]carnitine, but no association between the increase in carnitine uptake and blood flow was obtained. Co-immunostaining of OCTN2 and dystrophin (a muscle plasma membrane marker) showed an increase in OCTN2 signal in the plasma membrane after muscle contraction. Western blotting showed that the level of sarcolemmal OCTN2 was greater in contracting muscles than in resting muscles (p < 0.05). The present study showed that muscle contraction facilitated carnitine uptake in skeletal muscles, possibly via the contraction-induced translocation of its specific transporter OCTN2 to the plasma membrane.
Review of chemical and radiotoxicological properties of polonium for internal contamination purposes
The discovery of polonium (Po) was first published in July 1898 by P. and M. Curie. It was the first element to be discovered by the radiochemical method. Polonium can be considered as a famous but neglected element: only a few studies of polonium chemistry have been published, mostly between 1950 and 1990. The recent (2006) event in which 2106 Po evidently was used as a poison to kill A. Litvinenko has raised new interest in polonium. 2011 being the 100th 8 anniversary of Marie Curie Nobel Prize in Chemistry, the aim of this paper is to review several aspect of polonium linked to its chemical properties and its radiotoxicity, including : i) its radiochemistry and interaction with matter; ii) its main sources and uses; iii) its physico-chemical properties; iv) its main analytical methods; v) its background exposure risk in water, food, and other environmental media; vi) its biokinetics and distribution following inhalation, ingestion and wound contamination; vii) its dosimetry and viii) treatments available (decorporation) in case of internal contamination.
The study of equivalent dose of uranium in long bean (V. U. Sesquipedalis) and the effect on human
In the case of accidental release of Uranium-238 ({sup 238}U) radionuclides in a nuclear facility or in the environment, internal contamination by either acute or chronic exposure has the potential to induce both radiological and chemical toxic effects. A study was conducted to estimate the {sup 238}U radionuclide concentration in the long beans using Induced Coupled Mass Plasma-Spectrometry (ICP-MS). {sup 238}U radionuclide is a naturally occurring radioactive material that can be found in soil and can be transferred to the long bean (Vigna unguiculata subsp. Sesquapedalis) directly or indirectly via water or air. Kidney and liver are the major sites of deposition of {sup 238}U radionuclide. The obtained dose exposed in the liver and kidney is used to assess the safety level for public intake of {sup 238}U radionuclide from the consumption of long beans. The concentration of {sup 238}U radionuclide measured in long bean samples was 0.0226 ± 0.0009 mg/kg. Total activity of {sup 238}U radionuclide was 0.0044 ± 0.0002 Bq/day with the daily intake of 0.3545 ± 0.0143 µg/day and the annual committed effective dose due to ingestion of {sup 238}U radionuclide in long beans was 0.2230 ± 0.0087 µSv/year. The committed equivalent dose of {sup 238}U radionuclide from the assessment in the liver and kidney are 0.4198 ± 0.0165 nSv and 10.9335 ± 0.4288 nSv. The risk of cancer of {sup 238}U radionuclide was determined to be (86.0466 ± 3.3748) × 10-9. Thus, the results concluded that {sup 238}U radionuclide in local long beans was in the permitted level and safe to consume without posing any significant radiological threat to population.
Evaluation of internal contamination levels after a radiological dispersal device incident using portal monitors
Following a radioactive dispersal device (RDD) incident, it may be necessary to evaluate the internal contamination levels of a large number of potentially affected individuals to determine if immediate medical follow-up is necessary. Since the current laboratory capacity to screen for internal contamination is limited, rapid field screening methods can be useful in prioritizing individuals. This study evaluated the suitability of a radiation portal monitor for such screening. A model of the portal monitor was created for use with models of six anthropomorphic phantoms in Monte Carlo N-Particle Transport Code Version 5 (MCNP) X-5 Monte Carlo Team (MCNP A General Monte Carlo N-Particle Transport Code Version 5. LA-CP-03-0245. Vol. 2. Los Alamos National Laboratory, 2004.). The count rates of the portal monitor were simulated for inhalation and ingestion of likely radionuclides from an RDD for each of the phantoms. The time-dependant organ concentrations of the radionuclides were determined using Dose and Risk Calculation Software Eckerman, Leggett, Cristy, Nelson, Ryman, Sjoreen and Ward (Dose and Risk Calculation Software Ver. 8.4. ORNL/TM-2001/190. Oak Ridge National Laboratory, 2006.). Portal monitor count rates corresponding to a committed effective dose E(50) of 10 mSv are reported.
Mathematical efficiency calibration with uncertain source geometries using smart optimization
The In Situ Object Counting Software (ISOCS), a mathematical method developed by CANBERRA, is a well established technique for computing High Purity Germanium (HPGe) detector efficiencies for a wide variety of source shapes and sizes. In the ISOCS method, the user needs to input the geometry related parameters such as: the source dimensions, matrix composition and density, along with the source-to-detector distance. In many applications, the source dimensions, the matrix material and density may not be well known. Under such circumstances, the efficiencies may not be very accurate since the modeled source geometry may not be very representative of the measured geometry. CANBERRA developed an efficiency optimization software known as 'Advanced ISOCS' that varies the not well known parameters within user specified intervals and determines the optimal efficiency shape and magnitude based on available benchmarks in the measured spectra. The benchmarks could be results from isotopic codes such as MGAU, MGA, IGA, or FRAM, activities from multi-line nuclides, and multiple counts of the same item taken in different geometries (from the side, bottom, top etc). The efficiency optimization is carried out using either a random search based on standard probability distributions, or using numerical techniques that carry out a more directed (referred to as 'smart' in this paper) search. Measurements were carried out using representative source geometries and radionuclide distributions. The radionuclide activities were determined using the optimum efficiency and compared against the true activities. The 'Advanced ISOCS' method has many applications among which are: Safeguards, Decommissioning and Decontamination, Non-Destructive Assay systems and Nuclear reactor outages maintenance. (authors)
SU-C-201-06: Utility of Quantitative 3D SPECT/CT Imaging in Patient Specific Internal Dosimetry of 153-Samarium with GATE Monte Carlo Package
Purpose: Patient-specific 3-dimensional (3D) internal dosimetry in targeted radionuclide therapy is essential for efficient treatment. Two major steps to achieve reliable results are: 1) generating quantitative 3D images of radionuclide distribution and attenuation coefficients and 2) using a reliable method for dose calculation based on activity and attenuation map. In this research, internal dosimetry for 153-Samarium (153-Sm) was done by SPECT-CT images coupled GATE Monte Carlo package for internal dosimetry. Methods: A 50 years old woman with bone metastases from breast cancer was prescribed 153-Sm treatment (Gamma: 103keV and beta: 0.81MeV). A SPECT/CT scan was performed with the Siemens Simbia-T scanner. SPECT and CT images were registered using default registration software. SPECT quantification was achieved by compensating for all image degrading factors including body attenuation, Compton scattering and collimator-detector response (CDR). Triple energy window method was used to estimate and eliminate the scattered photons. Iterative ordered-subsets expectation maximization (OSEM) with correction for attenuation and distance-dependent CDR was used for image reconstruction. Bilinear energy mapping is used to convert Hounsfield units in CT image to attenuation map. Organ borders were defined by the itk-SNAP toolkit segmentation on CT image. GATE was then used for internal dose calculation. The Specific Absorbed Fractions (SAFs) and S-values were reported as MIRD schema. Results: The results showed that the largest SAFs and S-values are in osseous organs as expected. S-value for lung is the highest after spine that can be important in 153-Sm therapy. Conclusion: We presented the utility of SPECT-CT images and Monte Carlo for patient-specific dosimetry as a reliable and accurate method. It has several advantages over template-based methods or simplified dose estimation methods. With advent of high speed computers, Monte Carlo can be used for treatment planning on a day to day basis.
SU-E-I-78: Establishing a Protocol for Quick Estimation of Thyroid Internal Contamination with 131I in Normal and Emergency Situations
Purpose: I-131 is one of the most frequent radionuclides used in nuclear medicine departments. The radiation workers, who manipulate the unsealed radio-toxic iodine, should be monitored for internal contamination. In this study a protocol was established for estimating I-131 activity absorbed in the thyroid glands of the nuclear medicine staff in normal working condition and also in accidents. Methods: I-131 with the activity of 10 μCi was injected inside the thyroid gland of a home-made anthropomorphic neck phantom. The phantom is made up of PMMA as soft tissue, and Aluminium as bone. The dose rate at different distances from the surface of the neck phantom was measured using a scintillator detector for duration of two months. Then, calibration factors were obtained, for converting the dose rate at each distance to the iodine activity inside the thyroid. Results: According to the results of this study, the calibration factors for converting the dose rates (nSv/h) at distances of 0cm, 1cm, 6cm, 11cm, and 16cm to the activity (kBq) inside the thyroid were found to be 0.03, 0.04, 0.14, 0.29, and 0.49 . Conclusion: This method can be effectively used for quick estimation of the I-131 concentration inside the thyroid of the staff for daily checks in normal working conditions and also in accidents.
SU-E-I-82: PET Radiopharmaceuticals for Prostate Cancer Imaging: A Review
Purpose: The aim of this work was to review new and clinical practice PET radiopharmaceuticals for prostate cancer imaging. Methods: PET radiopharmaceuticals were reviewed on the main databases. Availability, dosimetry, accuracy and limitations were considered. Results: The following radioisotopes with respective physical half-life and mean positron energy were found: {sup 18}F (109,7 min, 249,8 keV), {sup 89}Zr (78,4 hs, 395,5 keV), {sup 11}C (20,4 min, 385,7 keV) and {sup 68}Ga (67,8 min, 836 keV). {sup 68}Ga was the only one not produced by cyclotron. Radiopharmaceuticals uptake by glucose metabolism ({sup 18}F-FDG), lipogenesis ({sup 11}C-Choline and {sup 11}C-Acetate), amino acid transport (Anti-{sup 18}F-FACBC), bone matrix ({sup 18}F-NaF), prostatespecific membrane antigen ({sup 68}Ga-PSMA and {sup 89}Zr-J591), CXCR receptors ({sup 89}Ga-Pentixafor), adrenal receptors ({sup 18}F-FDHT) and gastrin release peptide receptor (bombesin analogue). Most of radiopharmaceuticals are urinary excretion, so bladder is the critical organ. 11C-choline (pancreas), Anti-{sup 18}FFACBC (liver) and {sup 18}F-FBDC (stomach wall) are the exception. Higher effective dose was seen {sup 18}F-NaF (27 μSv/MBq) while the lowest was {sup 11}CAcetate (3,5 μSv/MBq). Conclusion: Even though {sup 18}F-FDG has a large availability its high urinary excretion and poor uptake to slow growing disease offers weak results for prostate cancer. Better accuracy is obtained when {sup 18}F-NaF is used for bone metastatic investigation although physicians tend to choose bone scintigraphy probably due to its cost and practice. Many guidelines in oncology consider {sup 11}C or {sup 18}F labeled with Choline the gold standard for biochemical relapse after radical treatment. Local, lymph node and distant metastatic relapse can be evaluated at same time with this radiopharmaceutical. There is no consensus over bigger urinary excretion for {sup 18}F labeling. Anti-{sup 18}F-FACBC, {sup 68}Ga-PSMA and {sup 68}Ga-Pentixafor are demonstrating good results but more researches are needed. While PSMA imaging seems to be independent of PSA level, one choline limitation, anti-{sup 18}F-FACBC adds value because imaging any disease stage. {sup 68}Ga-Petixafor is being tested as theranostics marker integrating molecular image and therapy.
SU-E-T-534: Level of Residual Radioactivity of Activated Parts of a Decommissioned Cyclotron
Purpose: CTI cyclotron RDS-111 was used at the Hong Kong Sanatorium and Hospital (HKSH) to produce radiopharmaceuticals and radioactive tracers for diagnostic scans between 1999 and 2007. During the operation, some machine components became radioactive by activation. For the safety of staff, decommissioning took place in 2009, two years after the cyclotron had stopped operation. This study investigates the residual radioactivity and radionuclides found in different cyclotron components in 2014 in compliance with the local regulations in Hong Kong for transfer of radioactive waste. Methods: A representative sample of each part was counted using a high-purity germanium detector (manufacturer: ORTECT) for at least four hours. GammaVision, a multichannel analyzer software, was used to identify the radionuclides found in the cyclotron components, as well as the associated activities. A standard library and a Mariscotti peak search algorithm were used to identify the present radionuclides. Only radionuclides with half-life greater than 180 days were considered. Results: Among the components, the Havar target foil has the highest specific activity ((4.6±0.6)×10{sup 2} Bq/g), with Co-60 being the most prominent ((3.8±0.5)×10{sup 2} Bq/g). The total activity of the target foil, however, is still low due to its small mass of 0.04 g. Radioisotopes Mn-54 (46±6 Bq/g), Na-22 (6.8±0.8 Bq/g), Co-57 (7.3±0.9 Bq/g), and Fe-59 (6.0±0.9 Bq/g) have also been detected in the target foil. The target window holder and the vacuum window register a specific activity of 88.3±0.6 Bq/g and 48.6±0.1 Bq/g, respectively. Other components, such as the collimator, the target tube, the valve body and the beamline, are also found with trace amounts of radionuclides. Conclusion: Even seven years after the cyclotron had stopped operation, some components still exhibited residual radioactivity from activation exceeding the IAEA clearance levels. Special consideration for radiological protection may need to be taken in the disposal of the cyclotron parts.
SU-E-T-667: Radiosensitization Due to Gold Nanoparticles: A Monte Carlo Cellular Dosimetry Investigation of An Expansive Parameter Space
Purpose: To investigate dose enhancement to cellular compartments following gold nanoparticle (GNP) uptake in tissue, varying cell and tissue morphology, intra and extracellular GNP distribution, and source energy using Monte Carlo (MC) simulations. Methods: Models of single and multiple cells are developed for normal and cancerous tissues; cells (outer radii 5–10 µm) are modeled as concentric spheres comprising the nucleus (radii 2.5–7.5 µm) and cytoplasm. GNP distributions modeled include homogeneous distributions throughout the cytoplasm, variable numbers of GNP-containing endosomes within the cytoplasm, or distributed in a spherical shell about the nucleus. Gold concentrations range from 1 to 30 mg/g. Dose to nucleus and to cytoplasm for simulations including GNPs are compared to simulations without GNPs to compute Nuclear and Cytoplasm Dose Enhancement Factors (NDEF, CDEF). Photon source energies are between 20 keV and 1.25 MeV. Results: DEFs are highly sensitive to GNP intracellular distribution; for a 2.5 µm radius nucleus irradiated by a 30 keV source, NDEF varies from 1.2 for a single endosome containing all GNPs to 8.2 for GNPs distributed about the nucleus (7 mg/g). DEFs vary with cell dimensions and source energy: NDEFs vary from 2.5 (90 keV) to 8.2 (30 keV) for a 2.5 µm radius nucleus and from 1.1 (90 keV) to 1.3 (30 keV) for a 7.5 µm radius nucleus, both with GNPs in a spherical shell about the nucleus (7 mg/g). NDEF and CDEF are generally different within a single cell. For multicell models, the presence of gold within intervening tissues between source and target perturbs the fluence reaching cellular targets, resulting in DEF inhomogeneities within a population of irradiated cells. Conclusion: DEFs vary by an order of magnitude for different cell models, GNP distributions, and source energies, demonstrating the importance of detailed modelling for advancing GNP development for radiotherapy. Funding provided by the Natural Sciences and Engineering Council of Canada (NSERC), and the Canada Research Chairs Program (CRC)
WE-H-207A-07: Image-Based Versus Atlas-Based Internal Dosimetry
Purpose: Monte Carlo (MC) simulation is known as the gold standard method for internal dosimetry. It requires radionuclide distribution from PET or SPECT and body structure from CT for accurate dose calculation. The manual or semi-automatic segmentation of organs from CT images is a major obstacle. The aim of this study is to compare the dosimetry results based on patient’s own CT and a digital humanoid phantom as an atlas with pre-specified organs. Methods: SPECT-CT images of a 50 year old woman who underwent bone pain palliation with Samarium-153 EDTMP for osseous metastases from breast cancer were used. The anatomical date and attenuation map were extracted from SPECT/CT and three XCAT digital phantoms with different BMIs (i.e. matched (38.8) and unmatched (35.5 and 36.7) with patient’s BMI that was 38.3). Segmentation of patient’s organs in CT image was performed using itk-SNAP software. GATE MC Simulator was used for dose calculation. Specific absorbed fractions (SAFs) and S-values were calculated for the segmented organs. Results: The differences between SAFs and S-values are high using different anatomical data and range from −13% to 39% for SAF values and −109% to 79% for S-values in different organs. In the spine, the clinically important target organ for Samarium Therapy, the differences in the S-values and SAF values are higher between XCAT phantom and CT when the phantom with identical BMI is employed (53.8% relative difference in S-value and 26.8% difference in SAF). However, the whole body dose values were the same between the calculations based on the CT and XCAT with different BMIs. Conclusion: The results indicated that atlas-based dosimetry using XCAT phantom even with matched BMI for patient leads to considerable errors as compared to image-based dosimetry that uses the patient’s own CT Patient-specific dosimetry using CT image is essential for accurate results.