TY - JOUR A1 - Tran-Gia, Johannes A1 - Denis-Bacelar, Ana M. A1 - Ferreira, Kelley M. A1 - Robinson, Andrew P. A1 - Calvert, Nicholas A1 - Fenwick, Andrew J. A1 - Finocchiaro, Domenico A1 - Fioroni, Federica A1 - Grassi, Elisa A1 - Heetun, Warda A1 - Jewitt, Stephanie J. A1 - Kotzassarlidou, Maria A1 - Ljungberg, Michael A1 - McGowan, Daniel R. A1 - Scott, Nathaniel A1 - Scuffham, James A1 - Gleisner, Katarina Sjögreen A1 - Tipping, Jill A1 - Wevrett, Jill A1 - Lassmann, Michael T1 - A multicentre and multi-national evaluation of the accuracy of quantitative Lu-177 SPECT/CT imaging performed within the MRTDosimetry project JF - EJNMMI Physics N2 - Purpose Patient-specific dosimetry is required to ensure the safety of molecular radiotherapy and to predict response. Dosimetry involves several steps, the first of which is the determination of the activity of the radiopharmaceutical taken up by an organ/lesion over time. As uncertainties propagate along each of the subsequent steps (integration of the time–activity curve, absorbed dose calculation), establishing a reliable activity quantification is essential. The MRTDosimetry project was a European initiative to bring together expertise in metrology and nuclear medicine research, with one main goal of standardizing quantitative \(^{177}\)Lu SPECT/CT imaging based on a calibration protocol developed and tested in a multicentre inter-comparison. This study presents the setup and results of this comparison exercise. Methods The inter-comparison included nine SPECT/CT systems. Each site performed a set of three measurements with the same setup (system, acquisition and reconstruction): (1) Determination of an image calibration for conversion from counts to activity concentration (large cylinder phantom), (2) determination of recovery coefficients for partial volume correction (IEC NEMA PET body phantom with sphere inserts), (3) validation of the established quantitative imaging setup using a 3D printed two-organ phantom (ICRP110-based kidney and spleen). In contrast to previous efforts, traceability of the activity measurement was required for each participant, and all participants were asked to calculate uncertainties for their SPECT-based activities. Results Similar combinations of imaging system and reconstruction lead to similar image calibration factors. The activity ratio results of the anthropomorphic phantom validation demonstrate significant harmonization of quantitative imaging performance between the sites with all sites falling within one standard deviation of the mean values for all inserts. Activity recovery was underestimated for total kidney, spleen, and kidney cortex, while it was overestimated for the medulla. Conclusion This international comparison exercise demonstrates that harmonization of quantitative SPECT/CT is feasible when following very specific instructions of a dedicated calibration protocol, as developed within the MRTDosimetry project. While quantitative imaging performance demonstrates significant harmonization, an over- and underestimation of the activity recovery highlights the limitations of any partial volume correction in the presence of spill-in and spill-out between two adjacent volumes of interests. KW - quantitative SPECT/CT KW - 177Lu SPECT/CT imaging KW - standardization of SPECT/CT imaging KW - harmonization of SPECT/CT imaging KW - international multicenter comparison exercise KW - traceability of SPECT/CT imaging KW - molecular radiotherapy (MRT) KW - 3D printing KW - phantom Y1 - 2021 U6 - http://nbn-resolving.de/urn/resolver.pl?urn:nbn:de:bvb:20-opus-270380 VL - 8 ER - TY - JOUR A1 - Soares Machado, J. A1 - Tran-Gia, J. A1 - Schlögl, S. A1 - Buck, A. K. A1 - Lassmann, M. T1 - Biokinetics, dosimetry, and radiation risk in infants after \(^{99m}\)Tc-MAG3 scans JF - EJNMMI Research N2 - Background: Renal scans are among the most frequent exams performed on infants and toddlers. Due to the young age, this patient group can be classified as a high-risk group with a higher probability for developing stochastic radiation effects compared to adults. As there are only limited data on biokinetics and dosimetry in this patient group, the aim of this study was to reassess the dosimetry and the associated radiation risk for infants undergoing \(^{99m}\)Tc-MAG3 renal scans based on a retrospective analysis of existing patient data. Consecutive data were collected from 20 patients younger than 20 months (14 males; 6 females) with normal renal function undergoing \(^{99m}\)Tc-MAG3 scans. To estimate the patient-specific organ activity, a retrospective calibration was performed based on a set of two 3D-printed infant kidneys filled with known activities. Both phantoms were scanned at different positions along the anteroposterior axis inside a water phantom, providing depth- and size-dependent attenuation correction factors for planar imaging. Time-activity curves were determined by drawing kidney, bladder, and whole-body regions-of-interest for each patient, and subsequently applying the calibration factor for conversion of counts to activity. Patient-specific time-integrated activity coefficients were obtained by integrating the organ-specific time-activity curves. Absorbed and effective dose coefficients for each patient were assessed with OLINDA/EXM for the provided newborn and 1-year-old model. The risk estimation was performed individually for each of the 20 patients with the NCI Radiation Risk Assessment Tool. Results: The mean age of the patients was 7.0 ± 4.5 months, with a weight between 5 and 12 kg and a body size between 60 and 89 cm. The injected activities ranged from 12 to 24 MBq of \(^{99m}\)Tc-MAG3. The patients' organ-specific mean absorbed dose coefficients were 0.04 ± 0.03 mGy/MBq for the kidneys and 0.27 ± 0.24 mGy/MBq for the bladder. The mean effective dose coefficient was 0.02 ± 0.02 mSv/MBq. Based on the dosimetry results, an evaluation of the excess lifetime risk for the development of radiation-induced cancer showed that the group of newborns has a risk of 16.8 per 100,000 persons, which is about 12% higher in comparison with the 1-year-old group with 14.7 per 100,000 persons (all values are given as mean plus/minus one standard deviation except otherwise specified). Conclusion: In this study, we retrospectively derived new data on biokinetics and dosimetry for infants with normal kidney function after undergoing renal scans with \(^{99m}\)Tc-MAG3. In addition, we analyzed the associated age- and gender-specific excess lifetime risk due to ionizing radiation. The radiation-associated stochastic risk increases with the organ doses, taking age- and gender-specific influences into account. Overall, the lifetime radiation risk associated with the \(^{99m}\)Tc-MAG3 scans is very low in comparison to the general population risk for developing cancer. KW - \(^{99m}\)Tc-MAG3 KW - absorbed dose KW - biokinetics KW - dosimetry KW - pediatric patients KW - risk assessment Y1 - 2018 U6 - http://nbn-resolving.de/urn/resolver.pl?urn:nbn:de:bvb:20-opus-175582 VL - 8 IS - 10 ER - TY - JOUR A1 - Tran-Gia, Johannes A1 - Denis-Bacelar, Ana M. A1 - Ferreira, Kelley M. A1 - Robinson, Andrew P. A1 - Bobin, Christophe A1 - Bonney, Lara M. A1 - Calvert, Nicholas A1 - Collins, Sean M. A1 - Fenwick, Andrew J. A1 - Finocchiaro, Domenico A1 - Fioroni, Federica A1 - Giannopoulou, Katerina A1 - Grassi, Elisa A1 - Heetun, Warda A1 - Jewitt, Stephanie J. A1 - Kotzasarlidou, Maria A1 - Ljungberg, Michael A1 - Lourenço, Valérie A1 - McGowan, Daniel R. A1 - Mewburn-Crook, Jamie A1 - Sabot, Benoit A1 - Scuffham, James A1 - Sjögreen Gleisner, Katarina A1 - Solc, Jaroslav A1 - Thiam, Cheick A1 - Tipping, Jill A1 - Wevrett, Jill A1 - Lassmann, Michael T1 - On the use of solid 133Ba sources as surrogate for liquid 131I in SPECT/CT calibration: a European multi-centre evaluation JF - EJNMMI Physics N2 - Introduction Commissioning, calibration, and quality control procedures for nuclear medicine imaging systems are typically performed using hollow containers filled with radionuclide solutions. This leads to multiple sources of uncertainty, many of which can be overcome by using traceable, sealed, long-lived surrogate sources containing a radionuclide of comparable energies and emission probabilities. This study presents the results of a quantitative SPECT/CT imaging comparison exercise performed within the MRTDosimetry consortium to assess the feasibility of using 133Ba as a surrogate for 131I imaging. Materials and methods Two sets of four traceable 133Ba sources were produced at two National Metrology Institutes and encapsulated in 3D-printed cylinders (volume range 1.68–107.4 mL). Corresponding hollow cylinders to be filled with liquid 131I and a mounting baseplate for repeatable positioning within a Jaszczak phantom were also produced. A quantitative SPECT/CT imaging comparison exercise was conducted between seven members of the consortium (eight SPECT/CT systems from two major vendors) based on a standardised protocol. Each site had to perform three measurements with the two sets of 133Ba sources and liquid 131I. Results As anticipated, the 131I pseudo-image calibration factors (cps/MBq) were higher than those for 133Ba for all reconstructions and systems. A site-specific cross-calibration reduced the performance differences between both radionuclides with respect to a cross-calibration based on the ratio of emission probabilities from a median of 12–1.5%. The site-specific cross-calibration method also showed agreement between 133Ba and 131I for all cylinder volumes, which highlights the potential use of 133Ba sources to calculate recovery coefficients for partial volume correction. Conclusion This comparison exercise demonstrated that traceable solid 133Ba sources can be used as surrogate for liquid 131I imaging. The use of solid surrogate sources could solve the radiation protection problem inherent in the preparation of phantoms with 131I liquid activity solutions as well as reduce the measurement uncertainties in the activity. This is particularly relevant for stability measurements, which have to be carried out at regular intervals. KW - 133Ba KW - Barium-133 KW - 131I KW - radioiodine KW - solid surrogate source KW - quantitative SPECT/CT KW - comparison exercise KW - multi-centre KW - calibration Y1 - 2023 U6 - http://nbn-resolving.de/urn/resolver.pl?urn:nbn:de:bvb:20-opus-357740 VL - 10 ER -