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Hjellström M, Isaksson M. Calibration of medical gamma cameras for estimation of internal contamination from 137Cs. JOURNAL OF RADIOLOGICAL PROTECTION : OFFICIAL JOURNAL OF THE SOCIETY FOR RADIOLOGICAL PROTECTION 2024; 44:021505. [PMID: 38530296 DOI: 10.1088/1361-6498/ad37c9] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Received: 01/06/2024] [Accepted: 03/26/2024] [Indexed: 03/27/2024]
Abstract
Calibration of 22 gamma camera units was performed at 15 hospitals in southern and western Sweden to estimate137Cs contamination in humans in a supine static geometry, with a new developed calibration protocol and phantom. The minimum detectable activities (MDAs) and the estimated committed effective doses (CEDs) were calculated for each calibration. Generic calibration factors were calculated for five predetermined groups based on the detector type and manufacturer. Group 1 and 2 included NaI-based gamma cameras from General Electrics (GEs) with a crystal thickness of 5/8'' and 3/8'' respectively. Group 3 and 4 included NaI-based gamma cameras from Siemens Healthineers with a crystal thickness of 3/8'', with a similar energy window as the GE NaI-based cameras and a dual window respectively. Group 5 included semiconductor-based gamma cameras from GE with a CdZnTe (CZT) detector. The generic calibration factors were 60.0 cps kBq-1, 52.3 cps kBq-1, 50.3 cps kBq-1, 53.2 cps kBq-1and 48.4 cps kBq-1for group 1, 2, 3, 4, and 5 respectively. The MDAs ranged between 169 and 1130 Bq for all groups, with measurement times of 1-10 min, corresponding to a CED of 4.77-77.6μSv. A dead time analysis was performed for group 1 and suggested a dead time of 3.17μs for137Cs measurements. The dead time analysis showed that a maximum count rate of 232 kcps could be measured in the calibration geometry, corresponding to a CED of 108-263 mSv. It has been shown that semiconductor-based gamma cameras with CZT detectors are feasible for estimating137Cs contamination. The generic calibration factors derived in this study can be used for gamma cameras of the same models in other hospitals, for measurements in the same measurement geometry. This will increase the measurement capability for estimating internal137Cs contamination in the recovery phase following radiological or nuclear events.
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Affiliation(s)
- Martin Hjellström
- Department of Medical Radiation Sciences, Institute of Clinical Sciences, Sahlgrenska Academy, University of Gothenburg, Gothenburg, Sweden
| | - Mats Isaksson
- Department of Medical Radiation Sciences, Institute of Clinical Sciences, Sahlgrenska Academy, University of Gothenburg, Gothenburg, Sweden
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Nakanishi K, Fujita N, Abe S, Nishii R, Kato K. A simple method to shorten the apparent dead time in the dosimetry of Lu-177 for targeted radionuclide therapy using a gamma camera. Phys Med 2024; 119:103298. [PMID: 38309102 DOI: 10.1016/j.ejmp.2024.103298] [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: 07/19/2023] [Revised: 12/04/2023] [Accepted: 01/23/2024] [Indexed: 02/05/2024] Open
Abstract
BACKGROUND The dead-time loss reportedly degrades the accuracy of dosimetry using a gamma camera for targeted radionuclide therapy with Lu-177; therefore, the dead-time loss needs to be corrected. However, the correction is challenging. In this study, we propose a novel and simple method to shorten the apparent dead time rather than correcting it through experiments and Monte Carlo simulations. METHODS An energy window of 208 keV ± 10 % is generally used for the imaging of Lu-177. Lower-energy gamma photons and X-rays of Lu-177 do not contribute to image formation but lead to dead-time losses. In our proposed method, a thin lead sheet was used to shield gamma photons and X-rays with energies lower than 208 keV, while detecting 208 keV gamma photons that penetrated the thin sheet. We measured and simulated the energy spectra and count rate characteristics of a clinical gamma camera system using a cylindrical phantom filled with a Lu-177 solution. Lead sheets of 1.0- and 0.5-mm thicknesses were used as thin shields, and the dead-time losses in tumour imaging with consumed Lu-177 were simulated. RESULTS The apparent dead times with lead sheets of 1.0- and 0.5-mm thicknesses and without a lead sheet were 1.7, 1.9, and 5.8 µs for an energy window of 208 keV ± 10 %, respectively. The dead-time losses could be reduced from 10 % to 1.3 % using the 1.0-mm thick lead sheet in the simulated imaging of tumour. CONCLUSION Our method is promising in clinical situations and studies on Lu-177 dosimetry for tumours.
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Affiliation(s)
- Kohei Nakanishi
- Functional Medical Imaging, Biomedical Imaging Sciences, Division of Advanced Information Health Sciences, Department of Integrated Health Sciences, Nagoya University Graduate School of Medicine, Nagoya, Japan.
| | - Naotoshi Fujita
- Department of Radiological Technology, Nagoya University Hospital, Nagoya, Japan
| | - Shinji Abe
- Department of Radiological Technology, Nagoya University Hospital, Nagoya, Japan
| | - Ryuichi Nishii
- Medical Imaging Engineering, Biomedical Imaging Sciences, Division of Advanced Information Health Sciences, Department of Integrated Health Sciences, Nagoya University Graduate School of Medicine, Nagoya, Japan
| | - Katsuhiko Kato
- Functional Medical Imaging, Biomedical Imaging Sciences, Division of Advanced Information Health Sciences, Department of Integrated Health Sciences, Nagoya University Graduate School of Medicine, Nagoya, Japan
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Desy A, Bouvet GF, Lafrenière N, Zamanian A, Després P, Beauregard JM. Impact of the dead-time correction method on quantitative 177Lu-SPECT (QSPECT) and dosimetry during radiopharmaceutical therapy. EJNMMI Phys 2022; 9:54. [PMID: 35976503 PMCID: PMC9385894 DOI: 10.1186/s40658-022-00484-w] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/01/2022] [Accepted: 08/08/2022] [Indexed: 11/10/2022] Open
Abstract
BACKGROUND Dead-time correction is required for accurate quantitative SPECT-based dosimetry in the context of personalised 177Lu radiopharmaceutical therapy. We aimed to evaluate the impact of applying dead-time correction on the reconstructed SPECT image versus on the acquisition projections before reconstruction. METHODS Data from 16 SPECT/CT acquisitions of a decaying 177Lu-filled phantom (up to 20.75 GBq) and dual-timepoint SPECT/CT in 14 patients treated with personalised 177Lu peptide receptor radionuclide therapy were analysed. Dead time was determined based on the acquisition wide-spectrum count rate for each projection and averaged for the entire acquisition. Three dead-time correction methods (DTCMs) were used: the per-projection correction, where each projection was individually corrected before reconstruction (DTCM1, the standard of reference), and two per-volume methods using the average dead-time correction factor of the acquisition applied to all projections before reconstruction (DTCM2) or to the SPECT image after reconstruction (DTCM3). Relative differences in quantification were assessed for various volumes of interest (VOIs) on the phantom and patient SPECT images. In patients, the resulting dosimetry estimates for tissues of interest were also compared between DTCMs. RESULTS Both per-volume DTCMs (DTCM2 and DTCM3) were found to be equivalent, with VOI count differences not exceeding 0.8%. When comparing the per-volume post-reconstruction DTCM3 versus the per-projection pre-reconstruction DTCM1, differences in VOI counts and absorbed dose estimates did not exceed 2%, with very few exceptions. The largest absorbed dose deviation was observed for a kidney at 3.5%. CONCLUSION While per-projection dead-time correction appears ideal for QSPECT, post-reconstruction correction is an acceptable alternative that is more practical to implement in the clinics, and that results in minimal deviations in quantitative accuracy and dosimetry estimates, as compared to the per-projection correction.
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Affiliation(s)
- Alessandro Desy
- Department of Medical Imaging, and Research Centre (Oncology Axis), CHU de Québec - Université Laval, 11 Côte du Palais, QC, G1R 2J6, Quebec City, Canada.,Department of Radiology and Nuclear Medicine, and Cancer Research Centre, Université Laval, Quebec City, Canada
| | - Guillaume F Bouvet
- Department of Medical Imaging, and Research Centre (Oncology Axis), CHU de Québec - Université Laval, 11 Côte du Palais, QC, G1R 2J6, Quebec City, Canada.,Department of Radiology and Nuclear Medicine, and Cancer Research Centre, Université Laval, Quebec City, Canada
| | - Nancy Lafrenière
- Department of Medical Imaging, and Research Centre (Oncology Axis), CHU de Québec - Université Laval, 11 Côte du Palais, QC, G1R 2J6, Quebec City, Canada
| | - Atefeh Zamanian
- Department of Medical Imaging, and Research Centre (Oncology Axis), CHU de Québec - Université Laval, 11 Côte du Palais, QC, G1R 2J6, Quebec City, Canada.,Department of Radiology and Nuclear Medicine, and Cancer Research Centre, Université Laval, Quebec City, Canada
| | - Philippe Després
- Department of Radiation Oncology, and Research Centre (Oncology Axis), CHU de Québec - Université Laval, Quebec City, Canada.,Department of Physics, Physical Engineering and Optics, and Cancer Research Centre, Université Laval, Quebec City, Canada
| | - Jean-Mathieu Beauregard
- Department of Medical Imaging, and Research Centre (Oncology Axis), CHU de Québec - Université Laval, 11 Côte du Palais, QC, G1R 2J6, Quebec City, Canada. .,Department of Radiology and Nuclear Medicine, and Cancer Research Centre, Université Laval, Quebec City, Canada.
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