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All sourcesNASA NTRSDOE OSTI
DOE OSTI2015

Safety of Radioembolization with {sup 90}Yttrium Resin Microspheres Depending on Coiling or No-Coiling of Aberrant/High-Risk Vessels

PurposeTo evaluate the safety of radioembolization (RE) with {sup 90}Yttrium ({sup 90}Y) resin microspheres depending on coiling or no-coiling of aberrant/high-risk vessels.Materials and MethodsEarly and late toxicity after 566 RE procedures were analyzed retrospectively in accordance with the National Cancer Institute’s Common Terminology Criteria for Adverse Events (CTCAE v3.0). For optimal safety, aberrant vessels were either coil embolized (n = 240/566, coiling group) or a more peripheral position of the catheter tip was chosen to treat right or left liver lobes (n = 326/566, no-coiling group).ResultsClinically relevant late toxicities (≥Grade 3) were observed in 1 % of our overall cohort. The no-coiling group had significantly less “any” (P = 0.0001) or “clinically relevant” (P = 0.0003) early toxicity. There was no significant difference (P > 0.05) in delayed toxicity in the coiling versus the no-coiling group. No RE-induced liver disease was noted after all 566 procedures.ConclusionRE with {sup 90}Y resin microspheres is a safe and effective treatment option. Performing RE without coil embolization of aberrant vessels prior to treatment could be an alternative for experienced centers.

62 RADIOLOGY AND NUCLEAR MEDICINE↗
DOE OSTI2017

Evaluation of Visualization Using a 50/50 (Contrast Media/Glucose 5% Solution) Technique for Radioembolization as an Alternative to a Standard Sandwich Technique

BackgroundRadioembolization (RE) with {sup 90}yttrium ({sup 90}Y) resin microspheres generally employs a sandwich technique with separate sequential administration of contrast medium (CM), followed by vehicle (e.g., glucose 5% [G5] solution), then {sup 90}Y resin microspheres (in G5), then G5, and then CM again to avoid contact of CM and microspheres under fluoroscopic guidance. This study evaluates the visualization quality and safety of a modified sandwich technique with a 50/50-mixture of CM (Imeron 300) and G5 for administration of {sup 90}Y resin microspheres.Materials and MethodsA retrospective analysis of 81 RE procedures in patients with primary or secondary liver tumors was performed. The quality of angiographic visualization of the hepatic vessels was assessed before the first injection and immediately before the whole dose has been injected. Visualization and flow rate were graded on a 5-point scale: 1 = very good to 5 = not visible/no antegrade flow. Univariate logistic regression models and multiple linear regression models were used to evaluate the prognostic variables associated with visualization and flow scores.ResultsVisualization quality was inversely related to flow rate, the lower the flow rate the better the grade of the visualization. Visualization quality was also inversely related to body-mass-index (BMI). Performing RE with the 50/50-CM/G5 mixture resulted in a mean injection time for 1 GBq of 15 min. No clinically significant adverse events, including radiation-induced liver disease were reported.ConclusionRE with a 50/50-mixture of CM and G5 for administration of {sup 90}Y resin microspheres in a modified sandwich technique is a safe administration alternative and provides good visualization of hepatic vessels, which is inversely dependent on flow rate and BMI. Injection time was reduced compared with our experience with the standard sandwich technique.

62 RADIOLOGY AND NUCLEAR MEDICINE↗
DOE OSTI2021

Use of X-Ray Fluorescence Microscopy for Studies on Research Models of Hepatocellular Carcinoma

Introduction: TheraSphere ® microspheres containing yttrium 90 Y are among many radioembolization agents used clinically to reduce liver tumor burden, and their effects on cancer volume reduction are well-established. At the same time, concerns about off target tissue injury often limit their use. Deeper investigation into tissue distribution and long-term impact of these microspheres could inform us about additional ways to use them in practice. Methods: Healthy rat liver and rabbit liver tumor samples from animals treated with TheraSpheres were sectioned and their elemental maps were generated by X-ray fluorescence microscopy (XFM) at the Advanced Photon Source (APS) synchrotron at Argonne National Laboratory (ANL). Results: Elemental imaging allowed us to identify the presence and distribution of TheraSpheres in animal tissues without the need for additional sample manipulation or staining. Ionizing radiation produced by 90 Y radioactive contaminants present in these microspheres makes processing TheraSphere treated samples complex. Accumulation of microspheres in macrophages was observed. Conclusions: This is the first study that used XFM to evaluate the location of microspheres and radionuclides in animal liver and tumor samples introduced through radioembolization. XFM has shown promise in expanding our understanding of radioembolization and could be used for investigation of human patient samples in the future.

60 APPLIED LIFE SCIENCES↗
DOE OSTI2016

WE-DE-201-05: Evaluation of a Windowless Extrapolation Chamber Design and Monte Carlo Based Corrections for the Calibration of Ophthalmic Applicators

Purpose: To test the validity of a windowless extrapolation chamber used to measure surface dose rate from planar ophthalmic applicators and to compare different Monte Carlo based codes for deriving correction factors. Methods: Dose rate measurements were performed using a windowless, planar extrapolation chamber with a {sup 90}Sr/{sup 90}Y Tracerlab RA-1 ophthalmic applicator previously calibrated at the National Institute of Standards and Technology (NIST). Capacitance measurements were performed to estimate the initial air gap width between the source face and collecting electrode. Current was measured as a function of air gap, and Bragg-Gray cavity theory was used to calculate the absorbed dose rate to water. To determine correction factors for backscatter, divergence, and attenuation from the Mylar entrance window found in the NIST extrapolation chamber, both EGSnrc Monte Carlo user code and Monte Carlo N-Particle Transport Code (MCNP) were utilized. Simulation results were compared with experimental current readings from the windowless extrapolation chamber as a function of air gap. Additionally, measured dose rate values were compared with the expected result from the NIST source calibration to test the validity of the windowless chamber design. Results: Better agreement was seen between EGSnrc simulated dose results and experimental current readings at very small air gaps (<100 µm) for the windowless extrapolation chamber, while MCNP results demonstrated divergence at these small gap widths. Three separate dose rate measurements were performed with the RA-1 applicator. The average observed difference from the expected result based on the NIST calibration was −1.88% with a statistical standard deviation of 0.39% (k=1). Conclusion: EGSnrc user code will be used during future work to derive correction factors for extrapolation chamber measurements. Additionally, experiment results suggest that an entrance window is not needed in order for an extrapolation chamber to provide accurate dose rate measurements for a planar ophthalmic applicator.

07 ISOTOPE AND RADIATION SOURCES↗
DOE OSTI2017

Beta-induced decrease in the content of the Si-II, Si-XII, Si-III, and α-Si silicon phases formed under an indenter

Volumes of the metastable Si-II, Si-XII, Si-III, and α-Si silicon phases in a locally deformed (Berkovich pyramid) region of unirradiated and beforehand irradiated Si single crystals are quantitatively estimated. Experimental data obtained by Raman spectroscopy and in situ detection of Si-I → Si-II silicon phase transformations under an indenter are used to calculate the volumes. The preliminary irradiation of silicon by β particles from a {sup 90}Sr–{sup 90}Y source (fluence F = 3.24 × 10{sup 10} cm{sup –2}, intensity I = 1.8 × 10{sup 5} cm{sup –2} s{sup –1}) reduces the volume of these phases by a factor of more than 1.5.

75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗
DOE OSTI2015

Study of influence of plastic scintillators thicknesses to detect Beta particles and Gamma radiation by means of spectral analysis of {sup 90}Sr, {sup 90}Y and {sup 137}Cs sources

The Nuclear and Energy Research Institute - IPEN, offers post-graduate programs, namely: Nuclear Technology - Applications (TNA), Nuclear Technology - Materials (TNM), Nuclear Technology - Reactors (TNR). The Institute programs mission is to form expert technicians, physicists and engineers with a strong knowledge in their discipline to work in the nuclear area. The course: 'Theoretical Fundamentals and Practices of the Instrumentation used in Nuclear Data Acquisition' covers the use of laboratory nuclear instrumentation and the accomplishment of experiments to obtain nuclear parameters. One of these experimental exercises is object of this work: 'Study of influence of plastic scintillators to detect Beta particles and Gamma radiation by means of spectral analysis of {sup 90}Sr, {sup 90}Y and {sup 137}Cs sources'. The use of scintillators plastic for the detection has the advantage of low cost, high mechanical strength, is not hygroscopic and can be manufactured in large volumes. This work aims to present the analysis of relative efficiency of detection of plastic scintillators of various thicknesses for beta particles and gamma radiation by the spectrum of {sup 137}Cs and {sup 90}Sr. Due to lack of resolution of the detectors plastic scintillators we worked with relative efficiency. The evaluation was done by reading deposited energy, using the software MAESTRO, for each detector thickness. For beta particles was observed an ideal thickness around 3 mm and the better photon efficiency was observed with increasing the thickness of the detector. The present experiment does not intend to establish a new technique for this subject: it solely aims student's practical exercises in nuclear properties of elements and detectors being part of the nuclear experimental course. (authors)

46 INSTRUMENTATION RELATED TO NUCLEAR SCIENCE AND ↗
DOE OSTI2016

Characterization of Sr-90 Drums at the Hanford 618-10 Burial Ground - 16132

The 618-10 Burial Ground on the Hanford Reservation was an early trench waste site used for the disposal of waste from the 300 Area at Hanford. Much of this waste consisted of residues from evaluations of failed fuel as well as various process and separations studies associated with the Department of Energy (DOE) mission which were performed in the 300 Area between March 1954 and September 1963. Historical records indicated that there were also several drums which contained significant quantities of separated Sr-90. Cleanup of the 618-10 burial ground is covered under the Washington Closure Hanford (WCH) contract. Due to the proximity of the 618-10 site to the Columbia River, waste is being removed from the 618-10 site, stabilized, and disposed of into either the Environmental Restoration Disposal Facility (ERDF) if the containers are determined to be LLW or transferred to the Hanford Central Waste Complex (CWC) if the containers are suspected to be TRU waste. In order to determine the correct disposal path, Non Destructive Assay (NDA) must be performed on all of the containers excavated from the trenches. The NDA of these containers is performed using germanium gamma spectroscopy with an In Situ Object Counting System (ISOCS) and with a neutron slab counter. Occasional ISOCS spectra exhibited a characteristic Sr-90/Y-90 Bremsstrahlung continuum. In some cases there were measurable gammas present, however in other cases only the Bremsstrahlung continuum was present. Typically Sr-90 is correlated to Cs-137 as they are normally produced in approximately a 1:1 ratio during the fission process. For some of these drums there was no Cs-137 detectable and therefore no way to quantify the Sr-90. Due to concerns about providing a reasonable and conservative nuclide inventory it was decided to evaluate a technique to utilize data from the Bremsstrahlung continuum to quantify the Sr-90 activity in these drums. The development of the technique combined MCNP modeling and comparison of measured gammas to the continuum for a well-defined waste stream. The final result showed reasonable correlation to the expected scaling factors for many drums, while also providing a reasonable measured value for drums with significantly enhanced Sr-90 concentrations. Ultimately all drums were demonstrated to be within the ERDF waste acceptance criteria. (authors)

12 MANAGEMENT OF RADIOACTIVE AND NON-RADIOACTIVE W↗
DOE OSTI2015

Performance of a Low Activity Beta-Sensitive SR{sup 90} Water Monitor for Fukushima

There are large volumes of contaminated water from the stabilization efforts at the damaged Fukushima Nuclear Power Plants. This water is being processed to remove radioactivity for eventual release to the environment. An on-line continuously operating system to confirm that the clean-up system is working properly, and to provide prompt feedback of the results is required by the system operator. While gamma emitting nuclides allow for the straight forward approach of gamma spectroscopy to identify and quantify radioactivity in water, pure beta emitting nuclides such as Sr{sup 90} pose a challenging problem. The relatively short range of beta radiation in water requires optimization of the measurement geometry in terms of the source-detector distance and source-detector interface while retaining a background sensitivity low enough to meet the Minimum Detectable Concentration (MDC) of 10 Bq/kg in 180 minutes. This issue is complicated by the continuum nature of the beta spectrum which does not allow for simple nuclide identification. The use of the Monte-Carlo code MCNP to estimate system performance before prototyping vastly increases the success of the end product. Various parameters such as detector size and thickness, water chamber size, water chamber construction materials were evaluated to help choose the optimum geometry. The final design was a system consisting of two large-area (16 x 35 cm) and thin (0.15 mm) plastic scintillators placed very close to a sealed a water chamber. The size of the chamber was optimized to obtain the maximum efficiency for the nuclide being measured (Sr/Y{sup 90}) but to minimize the efficiency for possible interferences (Ru/Rh{sup 106}, Cs{sup 137}). A thin carbon fiber window was selected with adequate material and thickness to contain the water under pressure, but also thin enough (0.5 mm) to allow enough beta radiation to pass through to the active detector volume. The entire measurement geometry is then housed in a thick lead shield to reduce contributions from external sources to an acceptable level. Data acquisition is accomplished through customized application-specific software that allows for long counting times to attain a low MDC, but also simultaneously provides alarms on short averaging times to achieve a fast response to sudden changes in activity concentration. Multiple monitors are then linked to supervisory software where real time data and alarms are available for analysis in remote locations. The system also allows for remote operation of the unit; check sources, background checks, systems settings and more may be accessed remotely. Testing of the production devices has shown that we can achieve the 10 Bk/kg MDC requirement for Sr{sup 90} in equilibrium with Y{sup 90} with a count time of approximately 20 minutes. (authors)

12 MANAGEMENT OF RADIOACTIVE AND NON-RADIOACTIVE W↗
DOE OSTI2018

Efficiency Calculation for an In-situ Beta Nuclide Monitoring System Based on a Plastic Scintillator - 18193

A plastic scintillator performance for an in-situ measurement system was analyzed using both simulation and experimental methods. The measurement results of four major pure beta-emitting radionuclides - namely H-3. C-14, P-32 and Sr-90/Y-90 - were compared with those from a Monte Carlo N-particle (MCNP) code simulation. Good agreement between the simulation and experimental results was observed for P-32 and Sr-90/Y-90. However, due to the short range of their beta particles in water, the efficiency for both H-3 and C-14 was rather low, and these radionuclides could not be detected. The optimal thickness for the plastic scintillator was identified, as was its suggested diameter. The effect of water depth on system performance was also considered. (authors)

12 MANAGEMENT OF RADIOACTIVE AND NON-RADIOACTIVE W↗
DOE OSTI2020

Identification and Quantification of Beta-Emitters in Waste Packages by Segmented Gamma-Scanning - 20114

A commonly applied method for the non-destructive characterization of the radioactive inventory of waste packages (e.g. 200-l drums) is segmented gamma-scanning. The gamma-emitting inventory is identified via their characteristic lines in the measured spectra. The corresponding net peak areas allow for quantification applying appropriate models. The identification and quantification of beta-emitters present in the waste package require further evaluation. While some of them emit gamma-rays, too, which can be used for identification and quantification, pure beta-emitters contribute to the gamma-spectra only by their Bremsstrahlung-spectra. {sup 32}P, {sup 90}Sr and {sup 90}Y are typical representatives of these isotopes. A method is developed for identification and quantification of these pure beta-emitters in radioactive waste packages. Origin of the procedure is the evaluation of the measured gamma-spectrum. After the identification of all lines present in the spectrum (characteristic gamma-lines, single- and double-escape-lines, X-ray-lines, annihilation peak etc.) this information is used together with calibration data of the detection system and further a-priori information like matrix composition, cross-section data from databases etc. to simulate the spectra without the Bremsstrahlung-components by an appropriate method. This may be Monte Carlo simulations or, like in our case, a computer code taking into account mathematical descriptions of the physical effects like photo effect, (multiple) Compton scattering, backscattering etc. and the attenuation effects of the waste matrix. In any case, the resulting spectrum must simulate the real spectrum without its Bremsstrahlung-component as good as possible. Subtracting the simulated from the measured spectrum then results in the Bremsstrahlung-components caused by the beta-emitters. Prior to evaluation, a set of Bremsstrahlung-spectra is calculated and stored for different beta-emitters in different matrices using the Bethe-Heitler equation. This data set can be extended for new conditions, if necessary, and is allocated in a data base for future application. Applying a non-linear optimization using the generalized reduced gradient method for comparing the calculated with the derived Bremsstrahlung-spectra results in the identification of the beta-emitter and a factor, which is proportional to its activity. The proportionality is determined by previous calibration measurements. The application of the method is demonstrated by measurements on a 200-l mock-up drum and a real waste package. (authors)

07 ISOTOPE AND RADIATION SOURCES↗
DOE OSTI2015

Comparative efficacy of 177 Lu and 90 Y for Anti-CD20 Pretargeted Radioimmunotherapy in Murine Lymphoma Xenograft Models

Purpose Pretargeted radioimmunotherapy (PRIT) is a multi-step method of selectively delivering high doses of radiotherapy to tumor cells while minimizing exposure to surrounding tissues. Yttrium-90 ( 90 Y) and lutetium-177 ( 177 Lu) are two of the most promising beta-particle emitting radionuclides used for radioimmunotherapy, which despite having similar chemistries differ distinctly in terms of radiophysical features. These differences may have important consequences for the absorbed dose to tumors and normal organs. Whereas 90 Y has been successfully applied in a number of preclinical and clinical radioimmunotherapy settings, there have been few published pretargeting studies with 177 Lu. We therefore compared the therapeutic potential of targeting either 90 Y or 177 Lu to human B-cell lymphoma xenografts in mice. Methods Parallel experiments evaluating the biodistribution, imaging, dosimetry, therapeutic efficacy, and toxicity were performed in female athymic nude mice bearing either Ramos (Burkitt lymphoma) or Granta (mantle cell lymphoma) xenografts, utilizing an anti-CD20 antibodystreptavidin conjugate (1F5-SA) and an 90 Y- or 177 Lu-labeled 1,4,7,10-tetraazacyclododecane-1,4,7,10-tetraacetic acid (DOTA)-biotin second step reagent. Results The two radionuclides displayed comparable biodistributions in tumors and normal organs; however, the absorbed radiation dose delivered to tumor was more than twice as high for 90 Y (1.3 Gy/MBq) as for 177 Lu (0.6 Gy/MBq). More importantly, therapy with 90 Y-DOTAbiotin was dramatically more effective than with 177 Lu-DOTA-biotin, with 100% of Ramos xenograft-bearing mice cured with 37 MBq 90 Y, whereas 0% were cured using identical amounts of 177 Lu-DOTA-biotin. Similar results were observed in mice bearing Granta xenografts, with 80% of the mice cured with 90 Y-PRIT and 0% cured with 177 Lu-PRIT. Toxicities were comparable with both isotopes. Conclusion 90 Y was therapeutically superior to 177 Lu for streptavidin-biotin PRIT approaches in these human lymphoma xenograft models.

62 RADIOLOGY AND NUCLEAR MEDICINE↗
DOE OSTI2019

99m Tc-, 90 Y-, and 177 Lu-Labeled Iron Oxide Nanoflowers Designed for Potential Use in Dual Magnetic Hyperthermia/Radionuclide Cancer Therapy and Diagnosis

Development of a complex based on iron oxide nanoparticles (IONPs) for diagnosis and dual magnetic hyperthermia/radionuclide cancer therapy accomplishing high yields of radiolabeling and great magnetic heat induction is still a challenge. We report here the synthesis of citric acid, poly(acrylic acid) (PAA) and poly(ethylene glycol) coated IONPs and their labeling with three radionuclides, namely, technetium (99mTc), yttrium (90Y), and lutetium (177Lu), aiming at potential use in cancer diagnosis and therapy. Polyol-synthesized IONPs are a flowerlike structure with 13.5 nm spherically shaped cores and 24.8 nm diameter. PAA-coated nanoparticles (PAA@IONP) showed the best characteristics such as easy radiolabeling with very high yields (>97.5%) with all three radionuclides, and excellent in vitro stabilities with less than 10% of radionuclides detaching after 24 h. Heating ability of PAA@IONP in an alternating external magnetic field showed intrinsic loss power value of 7.3 nH m2/kg, which is one of higher reported values. Additionally, PAA@IONP itself presented no significant cytotoxicity to the CT-26 cancer cells, reaching IC50 at 60 μg/mL. However, under the external magnetic field, they show hyperthermia-mediated cells killing, which correlated with the magnetic field strength and time of exposure. Since PAA@IONP are easy to prepare, biocompatible, and with excellent magnetic heat induction, these nanoparticles radiolabeled with high-energy beta emitters 90Y and 177Lu have valuable potential as agent for dual magnetic hyperthermia/radionuclide therapy, while radiolabeled with 99mTc could be used in diagnostic imaging. Copyright © 2019 American Chemical Society.

60 APPLIED LIFE SCIENCES↗
DOE OSTI2017

Prophylactic Temporary Occlusion of the Cystic Artery Using a Fibered Detachable Coil During {sup 90}Y Radioembolization

PurposeTo address the feasibility of prophylactic temporary occlusion of the cystic artery using a detachable coil during {sup 90}Y radioembolization.Materials and MethodsFrom January 2012 to October 2016, nine patients underwent temporary occlusion of the cystic artery during {sup 90}Y radioembolization. Based on the planning hepatic angiography, a detachable coil was deployed into the cystic artery, which arose from a more distal level (e.g., right anterior hepatic artery) than its usual origin, but the proximal 1 cm was left inside the microcatheter. {sup 90}Y microspheres were infused proximal to the cystic artery where the 99mTc-MAA had been infused, and then the coil was retrieved. Afterward, the patients underwent PET/CT imaging. Medical records were reviewed, and the differences in the uptake of 99mTc-MAA and {sup 90}Y microspheres in the gallbladder were evaluated using Wilcoxon’s signed-rank test.ResultsTemporary placement of a detachable coil was feasible in all cases. On the angiograms obtained after detachable coil placement, the distal cystic artery and gallbladder were partially identifiable in eight of the nine (88.8%) patients, but fully restored after the removal of the coils in all cases. The proportional uptake of 99mTc-MAA (mean, 4.35%) and {sup 90}Y (mean, 0.90%) in the gallbladder was significantly different due to the temporary occlusion of the cystic artery (p = 0.004). No clinical complications were identified for three months after the procedure.ConclusionTemporary occlusion of the cystic artery using a detachable coil appeared to be feasible and effective in reducing {sup 90}Y uptake in the gallbladder.

62 RADIOLOGY AND NUCLEAR MEDICINE↗
DOE OSTI2015

Monte Carlo simulation of PET and SPECT imaging of {sup 90}Y

Purpose: Yittrium-90 ({sup 90}Y) is traditionally thought of as a pure beta emitter, and is used in targeted radionuclide therapy, with imaging performed using bremsstrahlung single-photon emission computed tomography (SPECT). However, because {sup 90}Y also emits positrons through internal pair production with a very small branching ratio, positron emission tomography (PET) imaging is also available. Because of the insufficient image quality of {sup 90}Y bremsstrahlung SPECT, PET imaging has been suggested as an alternative. In this paper, the authors present the Monte Carlo-based simulation–reconstruction framework for {sup 90}Y to comprehensively analyze the PET and SPECT imaging techniques and to quantitatively consider the disadvantages associated with them. Methods: Our PET and SPECT simulation modules were developed using Monte Carlo simulation of Electrons and Photons (MCEP), developed by Dr. S. Uehara. PET code (MCEP-PET) generates a sinogram, and reconstructs the tomography image using a time-of-flight ordered subset expectation maximization (TOF-OSEM) algorithm with attenuation compensation. To evaluate MCEP-PET, simulated results of {sup 18}F PET imaging were compared with the experimental results. The results confirmed that MCEP-PET can simulate the experimental results very well. The SPECT code (MCEP-SPECT) models the collimator and NaI detector system, and generates the projection images and projection data. To save the computational time, the authors adopt the prerecorded {sup 90}Y bremsstrahlung photon data calculated by MCEP. The projection data are also reconstructed using the OSEM algorithm. The authors simulated PET and SPECT images of a water phantom containing six hot spheres filled with different concentrations of {sup 90}Y without background activity. The amount of activity was 163 MBq, with an acquisition time of 40 min. Results: The simulated {sup 90}Y-PET image accurately simulated the experimental results. PET image is visually superior to SPECT image because of the low background noise. The simulation reveals that the detected photon number in SPECT is comparable to that of PET, but the large fraction (approximately 75%) of scattered and penetration photons contaminates SPECT image. The lower limit of {sup 90}Y detection in SPECT image was approximately 200 kBq/ml, while that in PET image was approximately 100 kBq/ml. Conclusions: By comparing the background noise level and the image concentration profile of both the techniques, PET image quality was determined to be superior to that of bremsstrahlung SPECT. The developed simulation codes will be very useful in the future investigations of PET and bremsstrahlung SPECT imaging of {sup 90}Y.

07 ISOTOPE AND RADIATION SOURCES↗
DOE OSTI2016

A GATE evaluation of the sources of error in quantitative {sup 90}Y PET

Purpose: Accurate reconstruction of the dose delivered by {sup 90}Y microspheres using a postembolization PET scan would permit the establishment of more accurate dose–response relationships for treatment of hepatocellular carcinoma with {sup 90}Y. However, the quality of the PET data obtained is compromised by several factors, including poor count statistics and a very high random fraction. This work uses Monte Carlo simulations to investigate what impact factors other than low count statistics have on the quantification of {sup 90}Y PET. Methods: PET acquisitions of two phantoms—a NEMA PET phantom and the NEMA IEC PET body phantom-containing either {sup 90}Y or {sup 18}F were simulated using GATE. Simulated projections were created with subsets of the simulation data allowing the contributions of random, scatter, and LSO background to be independently evaluated. The simulated projections were reconstructed using the commercial software for the simulated scanner, and the quantitative accuracy of the reconstruction and the contrast recovery of the reconstructed images were evaluated. Results: The quantitative accuracy of the {sup 90}Y reconstructions were not strongly influenced by the high random fraction present in the projection data, and the activity concentration was recovered to within 5% of the known value. The contrast recovery measured for simulated {sup 90}Y data was slightly poorer than that for simulated {sup 18}F data with similar count statistics. However, the degradation was not strongly linked to any particular factor. Using a more restricted energy range to reduce the random fraction in the projections had no significant effect. Conclusions: Simulations of {sup 90}Y PET confirm that quantitative {sup 90}Y is achievable with the same approach as that used for {sup 18}F, and that there is likely very little margin for improvement by attempting to model aspects unique to {sup 90}Y, such as the much higher random fraction or the presence of bremsstrahlung in the singles data.

61 RADIATION PROTECTION AND DOSIMETRY↗
DOE OSTI2016

Practical reconstruction protocol for quantitative {sup 90}Y bremsstrahlung SPECT/CT

Purpose: To develop a practical background compensation (BC) technique to improve quantitative {sup 90}Y-bremsstrahlung single-photon emission computed tomography (SPECT)/computed tomography (CT) using a commercially available imaging system. Methods: All images were acquired using medium-energy collimation in six energy windows (EWs), ranging from 70 to 410 keV. The EWs were determined based on the signal-to-background ratio in planar images of an acrylic phantom of different thicknesses (2–16 cm) positioned below a {sup 90}Y source and set at different distances (15–35 cm) from a gamma camera. The authors adapted the widely used EW-based scatter-correction technique by modeling the BC as scaled images. The BC EW was determined empirically in SPECT/CT studies using an IEC phantom based on the sphere activity recovery and residual activity in the cold lung insert. The scaling factor was calculated from 20 clinical planar {sup 90}Y images. Reconstruction parameters were optimized in the same SPECT images for improved image quantification and contrast. A count-to-activity calibration factor was calculated from 30 clinical {sup 90}Y images. Results: The authors found that the most appropriate imaging EW range was 90–125 keV. BC was modeled as 0.53× images in the EW of 310–410 keV. The background-compensated clinical images had higher image contrast than uncompensated images. The maximum deviation of their SPECT calibration in clinical studies was lowest (<10%) for SPECT with attenuation correction (AC) and SPECT with AC + BC. Using the proposed SPECT-with-AC + BC reconstruction protocol, the authors found that the recovery coefficient of a 37-mm sphere (in a 10-mm volume of interest) increased from 39% to 90% and that the residual activity in the lung insert decreased from 44% to 14% over that of SPECT images with AC alone. Conclusions: The proposed EW-based BC model was developed for {sup 90}Y bremsstrahlung imaging. SPECT with AC + BC gave improved lesion detectability and activity quantification compared to SPECT with AC only. The proposed methodology can readily be used to tailor {sup 90}Y SPECT/CT acquisition and reconstruction protocols with different SPECT/CT systems for quantification and improved image quality in clinical settings.

61 RADIATION PROTECTION AND DOSIMETRY↗