1
|
Leube J, Claeys W, Gustafsson J, Salas-Ramirez M, Lassmann M, Koole M, Tran-Gia J. Position dependence of recovery coefficients in 177Lu-SPECT/CT reconstructions - phantom simulations and measurements. EJNMMI Phys 2024; 11:52. [PMID: 38937408 PMCID: PMC11211301 DOI: 10.1186/s40658-024-00662-y] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/11/2024] [Accepted: 06/17/2024] [Indexed: 06/29/2024] Open
Abstract
BACKGROUND Although the importance of quantitative SPECT has increased tremendously due to newly developed therapeutic radiopharmaceuticals, there are still no accreditation programs to harmonize SPECT imaging. Work is currently underway to develop an accreditation for quantitative 177Lu SPECT/CT. The aim of this study is to verify whether the positioning of the spheres within the phantom has an influence on the recovery and thus needs to be considered in SPECT harmonization. In addition, the effects of these recovery coefficients on a potential partial volume correction as well as absorbed-dose estimates are investigated. METHODS Using a low-dose CT of a SPECT/CT acquisition, a computerized version of the NEMA body phantom was created using a semi-automatic threshold-based method. Based on the mass-density map, the detector orbit, and the sphere centers, realistic SPECT acquisitions of all possible 720 sphere configurations of both the PET and the SPECT versions of the NEMA Body Phantom were generated using Monte Carlo simulations. SPECT reconstructions with different numbers of updates were performed without (CASToR) and with resolution modeling (STIR). Recovery coefficients were calculated for all permutations, reconstruction methods, and phantoms, and their dependence on the sphere positioning was investigated. Finally, the simulation-based findings were validated using SPECT/CT acquisitions of six different sphere configurations. RESULTS Our analysis shows that sphere positioning has a significant impact on the recovery for both of the reconstruction methods and the phantom type. Although resolution modeling resulted in significantly higher recovery, the relative variation in recovery within the 720 permutations was even larger. When examining the extreme values of the recovery, reconstructions without resolution modeling were influenced primarily by the sphere position, while with resolution modeling the volume of the two adjacent spheres had a larger influence. The SPECT measurements confirmed these observations, and the recovery curves showed good overall agreement with the simulated data. CONCLUSION Our study shows that sphere positioning has a significant impact on the recovery obtained in NEMA sphere phantom measurements and should therefore be considered in a future SPECT accreditation. Furthermore, the single-measurement method normally performed for PVC should be reconsidered to account for the position dependency.
Collapse
Affiliation(s)
- Julian Leube
- Department of Nuclear Medicine, University Hospital Würzburg, Oberdürrbacherstr. 6, Würzburg, 97080, Germany.
| | - Wies Claeys
- Department of Imaging and Pathology, KU Leuven, Herestraat 49, Leuven, 3000, Belgium
| | - Johan Gustafsson
- Medical Radiation Physics Lund, Lund University, Skåne University Hospital Lund, Lund, 221 85, Sweden
| | - Maikol Salas-Ramirez
- Department of Nuclear Medicine, University Hospital Würzburg, Oberdürrbacherstr. 6, Würzburg, 97080, Germany
| | - Michael Lassmann
- Department of Nuclear Medicine, University Hospital Würzburg, Oberdürrbacherstr. 6, Würzburg, 97080, Germany
| | - Michel Koole
- Department of Imaging and Pathology, KU Leuven, Herestraat 49, Leuven, 3000, Belgium
| | - Johannes Tran-Gia
- Department of Nuclear Medicine, University Hospital Würzburg, Oberdürrbacherstr. 6, Würzburg, 97080, Germany
| |
Collapse
|
2
|
Gawel J, Rogulski Z. The Challenge of Single-Photon Emission Computed Tomography Image Segmentation in the Internal Dosimetry of 177Lu Molecular Therapies. J Imaging 2024; 10:27. [PMID: 38276319 PMCID: PMC10817423 DOI: 10.3390/jimaging10010027] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/27/2023] [Revised: 01/03/2024] [Accepted: 01/05/2024] [Indexed: 01/27/2024] Open
Abstract
The aim of this article is to review the single photon emission computed tomography (SPECT) segmentation methods used in patient-specific dosimetry of 177Lu molecular therapy. Notably, 177Lu-labelled radiopharmaceuticals are currently used in molecular therapy of metastatic neuroendocrine tumours (ligands for somatostatin receptors) and metastatic prostate adenocarcinomas (PSMA ligands). The proper segmentation of the organs at risk and tumours in targeted radionuclide therapy is an important part of the optimisation process of internal patient dosimetry in this kind of therapy. Because this is the first step in dosimetry assessments, on which further dose calculations are based, it is important to know the level of uncertainty that is associated with this part of the analysis. However, the robust quantification of SPECT images, which would ensure accurate dosimetry assessments, is very hard to achieve due to the intrinsic features of this device. In this article, papers on this topic were collected and reviewed to weigh up the advantages and disadvantages of the segmentation methods used in clinical practice. Degrading factors of SPECT images were also studied to assess their impact on the quantification of 177Lu therapy images. Our review of the recent literature gives an insight into this important topic. However, based on the PubMed and IEEE databases, only a few papers investigating segmentation methods in 177Lumolecular therapy were found. Although segmentation is an important step in internal dose calculations, this subject has been relatively lightly investigated for SPECT systems. This is mostly due to the inner features of SPECT. What is more, even when studies are conducted, they usually utilise the diagnostic radionuclide 99mTc and not a therapeutic one like 177Lu, which could be of concern regarding SPECT camera performance and its overall outcome on dosimetry.
Collapse
Affiliation(s)
- Joanna Gawel
- Faculty of Chemistry, University of Warsaw, 02-093 Warsaw, Poland
| | | |
Collapse
|
3
|
Gustafsson J, Taprogge J. Future trends for patient-specific dosimetry methodology in molecular radiotherapy. Phys Med 2023; 115:103165. [PMID: 37880071 DOI: 10.1016/j.ejmp.2023.103165] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 05/31/2023] [Revised: 10/03/2023] [Accepted: 10/17/2023] [Indexed: 10/27/2023] Open
Abstract
Molecular radiotherapy is rapidly expanding, and new radiotherapeutics are emerging. The majority of treatments is still performed using empirical fixed activities and not tailored for individual patients. Molecular radiotherapy dosimetry is often seen as a promising candidate that would allow personalisation of treatments as outcome should ultimately depend on the absorbed doses delivered and not the activities administered. The field of molecular radiotherapy dosimetry has made considerable progress towards the feasibility of routine clinical dosimetry with reasonably accurate absorbed-dose estimates for a range of molecular radiotherapy dosimetry applications. A range of challenges remain with respect to the accurate quantification, assessment of time-integrated activity and absorbed dose estimation. In this review, we summarise a range of technological and methodological advancements, mainly focussed on beta-emitting molecular radiotherapeutics, that aim to improve molecular radiotherapy dosimetry to achieve accurate, reproducible, and streamlined dosimetry. We describe how these new technologies can potentially improve the often time-consuming considered process of dosimetry and provide suggestions as to what further developments might be required.
Collapse
Affiliation(s)
| | - Jan Taprogge
- National Radiotherapy Trials Quality Assurance (RTTQA) Group, Joint Department of Physics, Royal Marsden NHSFT, Downs Road, Sutton SM2 5PT, United Kingdom; The Institute of Cancer Research, 123 Old Brompton Road, London SW7 3RP, United Kingdom
| |
Collapse
|
4
|
Kim H, Li Z, Son J, Fessler JA, Dewaraja YK, Chun SY. Physics-Guided Deep Scatter Estimation by Weak Supervision for Quantitative SPECT. IEEE TRANSACTIONS ON MEDICAL IMAGING 2023; 42:2961-2973. [PMID: 37104110 PMCID: PMC10593395 DOI: 10.1109/tmi.2023.3270868] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 06/19/2023]
Abstract
Accurate scatter estimation is important in quantitative SPECT for improving image contrast and accuracy. With a large number of photon histories, Monte-Carlo (MC) simulation can yield accurate scatter estimation, but is computationally expensive. Recent deep learning-based approaches can yield accurate scatter estimates quickly, yet full MC simulation is still required to generate scatter estimates as ground truth labels for all training data. Here we propose a physics-guided weakly supervised training framework for fast and accurate scatter estimation in quantitative SPECT by using a 100× shorter MC simulation as weak labels and enhancing them with deep neural networks. Our weakly supervised approach also allows quick fine-tuning of the trained network to any new test data for further improved performance with an additional short MC simulation (weak label) for patient-specific scatter modelling. Our method was trained with 18 XCAT phantoms with diverse anatomies / activities and then was evaluated on 6 XCAT phantoms, 4 realistic virtual patient phantoms, 1 torso phantom and 3 clinical scans from 2 patients for 177Lu SPECT with single / dual photopeaks (113, 208 keV). Our proposed weakly supervised method yielded comparable performance to the supervised counterpart in phantom experiments, but with significantly reduced computation in labeling. Our proposed method with patient-specific fine-tuning achieved more accurate scatter estimates than the supervised method in clinical scans. Our method with physics-guided weak supervision enables accurate deep scatter estimation in quantitative SPECT, while requiring much lower computation in labeling, enabling patient-specific fine-tuning capability in testing.
Collapse
Affiliation(s)
- Hanvit Kim
- Digital Biomedical Research Division, Electronics and Telecommunications Research Institute, Daejeon, South Korea
- Department of Electrical Engineering, Ulsan National Institute of Science and Technology (UNIST), Ulsan, South Korea
| | - Zongyu Li
- Department of Electrical Engineering and Computer Science, University of Michigan, Ann Arbor, MI, USA
| | - Jiye Son
- Interdisciplinary Program for Bioengineering, Seoul National University (SNU), Seoul, South Korea. This work was done when she was with the School of Electrical and Computer Engineering (ECE), UNIST
| | - Jeffrey A. Fessler
- Department of Electrical Engineering and Computer Science, University of Michigan, Ann Arbor, MI, USA
| | - Yuni K. Dewaraja
- Dewaraja is with the Department of Radiology, University of Michigan, Ann Arbor, MI, USA
| | - Se Young Chun
- Department of ECE, INMC & IPAI, SNU, Seoul, South Korea
| |
Collapse
|
5
|
Pells S, Cullen DM, Deidda D, Denis-Bacelar AM, Fenwick A, Ferreira KM, Hamilton D, Heetun W, Julyan P, Needham G, Pietras B, Price E, Scuffham J, Tipping J, Robinson AP. Quantitative validation of Monte Carlo SPECT simulation: application to a Mediso AnyScan GATE simulation. EJNMMI Phys 2023; 10:60. [PMID: 37777689 PMCID: PMC10542438 DOI: 10.1186/s40658-023-00581-4] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/09/2023] [Accepted: 09/15/2023] [Indexed: 10/02/2023] Open
Abstract
BACKGROUND Monte Carlo (MC) simulations are used in nuclear medicine imaging as they provide unparalleled insight into processes that are not directly experimentally measurable, such as scatter and attenuation in an acquisition. Whilst MC is often used to provide a 'ground-truth', this is only the case if the simulation is fully validated against experimental data. This work presents a quantitative validation for a MC simulation of a single-photon emission computed tomography (SPECT) system. METHODS An MC simulation model of the Mediso AnyScan SCP SPECT system installed at the UK National Physical Laboratory was developed in the GATE (Geant4 Application for Tomographic Emission) toolkit. Components of the detector head and two collimator configurations were modelled according to technical specifications and physical measurements. Experimental detection efficiency measurements were collected for a range of energies, permitting an energy-dependent intrinsic camera efficiency correction function to be determined and applied to the simulation on an event-by-event basis. Experimental data were collected in a range of geometries with [Formula: see text]Tc for comparison to simulation. The procedure was then repeated with [Formula: see text]Lu to determine how the validation extended to another isotope and set of collimators. RESULTS The simulation's spatial resolution, sensitivity, energy spectra and the projection images were compared with experimental measurements. The simulation and experimental uncertainties were determined and propagated to all calculations, permitting the quantitative agreement between simulated and experimental SPECT acquisitions to be determined. Statistical agreement was seen in sinograms and projection images of both [Formula: see text]Tc and [Formula: see text]Lu data. Average simulated and experimental sensitivity ratios of ([Formula: see text]) were seen for emission and scatter windows of [Formula: see text]Tc, and ([Formula: see text]) and ([Formula: see text]) for the 113 and 208 keV emissions of [Formula: see text]Lu, respectively. CONCLUSIONS MC simulations will always be an approximation of a physical system and the level of agreement should be assessed. A validation method is presented to quantify the level of agreement between a simulation model and a physical SPECT system.
Collapse
Affiliation(s)
- Sophia Pells
- Department of Physics and Astronomy, The University of Manchester, Manchester, UK.
- National Physical Laboratory, Teddington, UK.
- Department of Radiology, UMass Chan Medical School, Worcester, MA, USA.
| | - David M Cullen
- Department of Physics and Astronomy, The University of Manchester, Manchester, UK
| | | | | | | | | | | | | | - Peter Julyan
- The Christie NHS Foundation Trust, Manchester, UK
| | - George Needham
- Department of Physics and Astronomy, The University of Manchester, Manchester, UK
- The Christie NHS Foundation Trust, Manchester, UK
| | - Ben Pietras
- Department of Physics and Astronomy, The University of Manchester, Manchester, UK
| | - Emlyn Price
- Department of Physics and Astronomy, The University of Manchester, Manchester, UK
| | - James Scuffham
- National Physical Laboratory, Teddington, UK
- Royal Surrey County Hospital, Guildford, UK
| | - Jill Tipping
- The Christie NHS Foundation Trust, Manchester, UK
| | - Andrew P Robinson
- Department of Physics and Astronomy, The University of Manchester, Manchester, UK
- National Physical Laboratory, Teddington, UK
- The Christie NHS Foundation Trust, Manchester, UK
| |
Collapse
|
6
|
Mikalsen LTG, Kvassheim M, Stokke C. Optimized SPECT Imaging of 224Ra α-Particle Therapy by 212Pb Photon Emissions. J Nucl Med 2023:jnumed.122.264455. [PMID: 37268424 DOI: 10.2967/jnumed.122.264455] [Citation(s) in RCA: 5] [Impact Index Per Article: 5.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/07/2022] [Revised: 03/10/2023] [Indexed: 06/04/2023] Open
Abstract
In preparation for an α-particle therapy trial using 1-7 MBq of 224Ra, the feasibility of tomographic SPECT/CT imaging was of interest. The nuclide decays in 6 steps to stable 208Pb, with 212Pb as the principle photon-emitting nuclide. 212Bi and 208Tl emit high-energy photons up to 2,615 keV. A phantom study was conducted to determine the optimal acquisition and reconstruction protocol. Methods: The spheres of a body phantom were filled with a 224Ra-RaCl2 solution, and the background compartment was filled with water. Images were acquired on a SPECT/CT system. In addition, 30-min scans were acquired for 80- and 240-keV emissions, using triple-energy windows, with both medium-energy and high-energy collimators. Images were acquired at 90-95 and 29-30 kBq/mL, plus an explorative 3-min acquisition at 20 kBq/mL (using only the optimal protocol). Reconstructions were performed with attenuation correction only, attenuation plus scatter correction, 3 levels of postfiltering, and 24 levels of iterative updates. Acquisitions and reconstructions were compared using the maximum value and signal-to-scatter peak ratio for each sphere. Monte Carlo simulations were performed to examine the contributions of key emissions. Results: Secondary photons of the 2,615-keV 208Tl emission produced in the collimators make up most of the acquired energy spectrum, as revealed by Monte Carlo simulations, with only a small fraction (3%-6%) of photons in each window providing useful information for imaging. Still, decent image quality is possible at 30 kBq/mL, and nuclide concentrations are imageable down to approximately 2-5 kBq/mL. The overall best results were obtained with the 240-keV window, medium-energy collimator, attenuation and scatter correction, 30 iterations and 2 subsets, and a 12-mm gaussian postprocessing filter. However, all combinations of the applied collimators and energy windows were capable of producing adequate results, even though some failed to reconstruct the 2 smallest spheres. Conclusion: SPECT/CT imaging of 224Ra in equilibrium with daughters is possible, with sufficient image quality to provide clinical utility for the current trial of intraperitoneally administrated activity. A systematic scheme for optimization was designed to select acquisition and reconstruction settings.
Collapse
Affiliation(s)
- Lars Tore Gyland Mikalsen
- Division of Radiology and Nuclear Medicine, Oslo University Hospital, Oslo, Norway;
- Department of Life Sciences and Health, Oslo Metropolitan University, Oslo, Norway
| | - Monika Kvassheim
- Division of Radiology and Nuclear Medicine, Oslo University Hospital, Oslo, Norway
- Faculty of Medicine, University of Oslo, Oslo, Norway; and
| | - Caroline Stokke
- Division of Radiology and Nuclear Medicine, Oslo University Hospital, Oslo, Norway
- Department of Physics, University of Oslo, Oslo, Norway
| |
Collapse
|
7
|
Miwa K, Nemoto R, Masuko H, Yamao T, Kobayashi R, Miyaji N, Inoue K, Onodera H. Evaluation of quantitative accuracy among different scatter corrections for quantitative bone SPECT/CT imaging. PLoS One 2022; 17:e0269542. [PMID: 35666737 PMCID: PMC9170091 DOI: 10.1371/journal.pone.0269542] [Citation(s) in RCA: 3] [Impact Index Per Article: 1.5] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/10/2021] [Accepted: 05/23/2022] [Indexed: 11/19/2022] Open
Abstract
Although scatter correction improves SPECT image contrast and thus image quality, the effects of quantitation accuracy under various conditions remain unclear. The present study aimed to empirically define the conditions for the optimal scatter correction of quantitative bone SPECT/CT images. Scatter correction was performed by applying dual and triple energy windows (DEW and TEW) with different sub-energy window widths, and effective scatter source estimation (ESSE) to CT-based scatter correction. Scattered radiation was corrected on images acquired using a triple line source (TLSP) phantom and an uniform cylinder phantom. The TLSP consisted of a line source containing 74.0 MBq of 99mTc in the middle, and a background component containing air, water or a K2HPO4 solution with a density equivalent to that of bone. The sum of all pixels in air, water and the K2HPO4 solution was measured on SPECT images. Scatter fraction (SF) and normalized mean square error (NMSE) based on counts from the air background as a reference were then calculated to assess quantitative errors due to scatter correction. The uniform cylinder phantom contained the same K2HPO4 solution and 222.0 MBq of 99mTc. The coefficient of variation (CV) was calculated from the count profile of this phantom to assess the uniformity of SPECT images across scatter correction under various conditions. Both SF and NMSE in SPECT images of phantoms containing water in the background were lower at a TEW sub-window of 3% (TEW3%), than in other scatter corrections, whereas those in K2HPO4 were lower at a DEW sub-window of 20% (DEW20%). Larger DEW and smaller TEW sub-energy windows allowed more effective correction. The CV of the uniform cylinder phantom, DEW20%, was inferior to all other tested scatter corrections. The quantitative accuracy of bone SPECT images substantially differed according to the method of scatter correction. The optimal scatter correction for quantitative bone SPECT was DEW20% (k = 1), but at the cost of slightly decreased image uniformity.
Collapse
Affiliation(s)
- Kenta Miwa
- Department of Radiological Sciences, School of Health Sciences, Fukushima Medical University, Fukushima, Japan
- Department of Radiological Sciences, School of Health Sciences, International University of Health and Welfare, Tochigi, Japan
- * E-mail:
| | - Reo Nemoto
- Department of Radiological Sciences, School of Health Sciences, International University of Health and Welfare, Tochigi, Japan
| | - Hirotsugu Masuko
- Department of Radiological Sciences, School of Health Sciences, International University of Health and Welfare, Tochigi, Japan
| | - Tensho Yamao
- Department of Radiological Sciences, School of Health Sciences, Fukushima Medical University, Fukushima, Japan
- Department of Radiological Sciences, School of Health Sciences, International University of Health and Welfare, Tochigi, Japan
| | - Rinya Kobayashi
- Department of Radiological Sciences, School of Health Sciences, International University of Health and Welfare, Tochigi, Japan
| | - Noriaki Miyaji
- Department of Nuclear Medicine, Cancer Institute Hospital of Japanese Foundation for Cancer Research, Tokyo, Japan
| | - Kosuke Inoue
- Department of Radiological Sciences, School of Health Sciences, International University of Health and Welfare, Tochigi, Japan
| | - Hiroya Onodera
- Department of Radiological Sciences, School of Health Sciences, International University of Health and Welfare, Tochigi, Japan
| |
Collapse
|
8
|
Craig AJ, Rojas B, Wevrett JL, Hamer E, Fenwick A, Gregory R. IPEM topical report: current molecular radiotherapy service provision and guidance on the implications of setting up a dosimetry service. Phys Med Biol 2020; 65:245038. [PMID: 33142274 DOI: 10.1088/1361-6560/abc707] [Citation(s) in RCA: 5] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/13/2022]
Abstract
Despite a growth in molecular radiotherapy treatment (MRT) and an increase in interest, centres still rarely perform MRT dosimetry. The aims of this report were to assess the main reasons why centres are not performing MRT dosimetry and provide advice on the resources required to set-up such a service. A survey based in the United Kingdom was developed to establish how many centres provide an MRT dosimetry service and the main reasons why it is not commonly performed. Twenty-eight per cent of the centres who responded to the survey performed some form of dosimetry, with 88% of those centres performing internal dosimetry. The survey showed that a 'lack of clinical evidence', a 'lack of guidelines' and 'not current UK practice' were the largest obstacles to setting up an MRT dosimetry service. More practical considerations, such as 'lack of software' and 'lack of staff training/expertise', were considered to be of lower significance by the respondents. Following on from the survey, this report gives an overview of the current guidelines, and the evidence available demonstrating the benefits of performing MRT dosimetry. The resources required to perform such techniques are detailed with reference to guidelines, training resources and currently available software. It is hoped that the information presented in this report will allow MRT dosimetry to be performed more frequently and in more centres, both in routine clinical practice and in multicentre trials. Such trials are required to harmonise dosimetry techniques between centres, build on the current evidence base, and provide the data necessary to establish the dose-response relationship for MRT.
Collapse
Affiliation(s)
- Allison J Craig
- Joint Department of Physics, Royal Marsden NHSFT, Sutton, United Kingdom. The Institute of Cancer Research, London, United Kingdom. Author to whom any correspondence should be addressed
| | | | | | | | | | | |
Collapse
|
9
|
Frezza A, Desport C, Uribe C, Zhao W, Celler A, Després P, Beauregard JM. Comprehensive SPECT/CT system characterization and calibration for 177Lu quantitative SPECT (QSPECT) with dead-time correction. EJNMMI Phys 2020; 7:10. [PMID: 32060777 PMCID: PMC7021856 DOI: 10.1186/s40658-020-0275-6] [Citation(s) in RCA: 16] [Impact Index Per Article: 4.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/29/2019] [Accepted: 01/26/2020] [Indexed: 12/31/2022] Open
Abstract
Background Personalization of 177Lu-based radionuclide therapy requires implementation of dosimetry methods that are both accurate and practical enough for routine clinical use. Quantitative single-photon emission computed tomography/computed tomography (QSPECT/CT) is the preferred scanning modality to achieve this and necessitates characterizing the response of the camera, and calibrating it, over the full range of therapeutic activities and system capacity. Various methods to determine the camera calibration factor (CF) and the deadtime constant (τ) were investigated, with the aim to design a simple and robust protocol for quantitative 177Lu imaging. Methods The SPECT/CT camera was equipped with a medium energy collimator. Multiple phantoms were used to reproduce various attenuation conditions: rod sources in air or water-equivalent media, as well as a Jaszczak phantom with inserts. Planar and tomographic images of a wide range of activities were acquired, with multiple energy windows for scatter correction (double or triple energy window technique) as well as count rate monitoring over a large spectrum of energy. Dead time was modelled using the paralysable model. CF and τ were deduced by curve fitting either separately in two steps (CF determined first using a subset of low-activity acquisitions, then τ determined using the full range of activity) or at once (both CF and τ determined using the full range of activity). Total or segmented activity in the SPECT field of view was computed. Finally, these methods were compared in terms of accuracy to recover the known activity, in particular when planar-derived parameters were applied to the SPECT data. Results The SPECT camera was shown to operate as expected on a finite count rate range (up to ~ 350 kcps over the entire energy spectrum). CF and τ from planar (sources in air) and SPECT segmented Jaszczak data yielded a very good agreement (CF < 1% and τ < 3%). Determining CF and τ from a single curve fit made dead-time-corrected images less prone to overestimating recovered activity. Using triple-energy window scatter correction while acquiring one or more additional energy window(s) to enable wide-spectrum count rate monitoring (i.e. ranging 55–250 or 18–680 keV) yielded the most consistent results across the various geometries. The final, planar-derived calibration parameters for our system were a CF of 9.36 ± 0.01 cps/MBq and a τ of 0.550 ± 0.003 μs. Using the latter, the activity in a Jaszczak phantom could be quantified by QSPECT with an accuracy of 0.02 ± 1.10%. Conclusions Serial planar acquisitions of sources in air using an activity range covering the full operational capacity of the SPECT/CT system, with multiple energy windows for wide-spectrum count rate monitoring, and followed by simultaneous determination of CF and τ using a single equation derived from the paralysable model, constitutes a practical method to enable accurate dead-time-corrected QSPECT imaging in a post-177Lu radionuclide therapy setting.
Collapse
Affiliation(s)
- Andrea Frezza
- Cancer Research Center, Université Laval, Quebec City, QC, Canada.,Department of Physics, Engineering Physics and Optics, Université Laval, Quebec City, QC, Canada.,Oncology Division, CHU de Québec - Université Laval Research Center, Quebec City, QC, Canada
| | - Corentin Desport
- Cancer Research Center, Université Laval, Quebec City, QC, Canada.,Department of Physics, Engineering Physics and Optics, Université Laval, Quebec City, QC, Canada.,Oncology Division, CHU de Québec - Université Laval Research Center, Quebec City, QC, Canada
| | - Carlos Uribe
- Functional Imaging Department, BC Cancer, Vancouver, BC, Canada
| | - Wei Zhao
- Medical Imaging Research Group, Department of Radiology, University of British Columbia, Vancouver, BC, Canada
| | - Anna Celler
- Medical Imaging Research Group, Department of Radiology, University of British Columbia, Vancouver, BC, Canada
| | - Philippe Després
- Cancer Research Center, Université Laval, Quebec City, QC, Canada.,Department of Physics, Engineering Physics and Optics, Université Laval, Quebec City, QC, Canada.,Oncology Division, CHU de Québec - Université Laval Research Center, Quebec City, QC, Canada.,Department of Radiation Oncology, CHU de Québec - Université Laval, Quebec City, QC, Canada
| | - Jean-Mathieu Beauregard
- Cancer Research Center, Université Laval, Quebec City, QC, Canada. .,Oncology Division, CHU de Québec - Université Laval Research Center, Quebec City, QC, Canada. .,Department of Radiology and Nuclear Medicine, Université Laval, Quebec City, QC, Canada. .,Department of Medical Imaging, CHU de Québec - Université Laval, 11 côte du Palais, Quebec City, QC, G1R 2J6, Canada.
| |
Collapse
|
10
|
Esquinas PL, Rodríguez-Rodríguez C, Esposito TVF, Harboe J, Bergamo M, Celler A, Saatchi K, Sossi V, Häfeli UO. Dual SPECT imaging of 111In and 67Ga to simultaneously determine in vivo the pharmacokinetics of different radiopharmaceuticals: a quantitative tool in pre-clinical research. ACTA ACUST UNITED AC 2018; 63:235029. [DOI: 10.1088/1361-6560/aaef63] [Citation(s) in RCA: 4] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/12/2022]
|
11
|
Karimi Ghodoosi E, D'Alessandria C, Li Y, Bartel A, Köhner M, Höllriegl V, Navab N, Eiber M, Li WB, Frey E, Ziegler S. The effect of attenuation map, scatter energy window width, and volume of interest on the calibration factor calculation in quantitative 177Lu SPECT imaging: Simulation and phantom study. Phys Med 2018; 56:74-80. [DOI: 10.1016/j.ejmp.2018.11.009] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 07/07/2018] [Revised: 11/07/2018] [Accepted: 11/15/2018] [Indexed: 10/27/2022] Open
|
12
|
Esquinas PL, Uribe CF, Gonzalez M, Rodríguez-Rodríguez C, Häfeli UO, Celler A. Accuracy of Rhenium-188 SPECT/CT activity quantification for applications in radionuclide therapy using clinical reconstruction methods. Phys Med Biol 2017; 62:6379-6396. [PMID: 28726679 DOI: 10.1088/1361-6560/aa7926] [Citation(s) in RCA: 7] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/12/2022]
Abstract
The main applications of 188Re in radionuclide therapies include trans-arterial liver radioembolization and palliation of painful bone-metastases. In order to optimize 188Re therapies, the accurate determination of radiation dose delivered to tumors and organs at risk is required. Single photon emission computed tomography (SPECT) can be used to perform such dosimetry calculations. However, the accuracy of dosimetry estimates strongly depends on the accuracy of activity quantification in 188Re images. In this study, we performed a series of phantom experiments aiming to investigate the accuracy of activity quantification for 188Re SPECT using high-energy and medium-energy collimators. Objects of different shapes and sizes were scanned in Air, non-radioactive water (Cold-water) and water with activity (Hot-water). The ordered subset expectation maximization algorithm with clinically available corrections (CT-based attenuation, triple-energy window (TEW) scatter and resolution recovery was used). For high activities, the dead-time corrections were applied. The accuracy of activity quantification was evaluated using the ratio of the reconstructed activity in each object to this object's true activity. Each object's activity was determined with three segmentation methods: a 1% fixed threshold (for cold background), a 40% fixed threshold and a CT-based segmentation. Additionally, the activity recovered in the entire phantom, as well as the average activity concentration of the phantom background were compared to their true values. Finally, Monte-Carlo simulations of a commercial [Formula: see text]-camera were performed to investigate the accuracy of the TEW method. Good quantification accuracy (errors <10%) was achieved for the entire phantom, the hot-background activity concentration and for objects in cold background segmented with a 1% threshold. However, the accuracy of activity quantification for objects segmented with 40% threshold or CT-based methods decreased (errors >15%), mostly due to partial-volume effects. The Monte-Carlo simulations confirmed that TEW-scatter correction applied to 188Re, although practical, yields only approximate estimates of the true scatter.
Collapse
Affiliation(s)
- Pedro L Esquinas
- Department of Physics and Astronomy, University of British Columbia, Vancouver, BC V6T 1Z1, Canada
| | | | | | | | | | | |
Collapse
|