- Email: [email protected]
CT
264
Abstracts / Physica Medica 56 (2018) 133–278
morpho-functional assessment of activity distribution, a further step is needed to evaluate the local dose. Methods. Preliminary gamma-camera calibrations (sensitivity and transmission curves) for 223Ra were performed. After estimating the metastatic activity and volume through scintigraphic images, the target absorbed dose is given by the ratio between energy and mass. While the latter can be evaluated from the same images, the local energy depends on the physical characteristics of the emitted radiation and the cumulated activity. In this way, both the energy per Bq released by each radiation type and its fraction locally deposited can be calculated. Cumulated activity requires data on the Xofigo kinetics over time, available in literature. Results. Starting from the relative radiation emissions by 223Ra, 219Rn, 211Po, 211Bi and 207Tl the following MeV/Bq values were obtained: 26.3 alpha (95.33%), 1.0 beta (3.64%) and 0.3 X and gamma (1.03%). While charged particles energies are completely released to the biological mass, tissue absorption coefficients and target thickness must be considered for photons. By applying these criteria to a 118 cm3metastatic localization, a 0.35 MBq initial activity and a 4.73d effective half-life (see table and figures), the 6.7 Gy dose was obtained. This value concerns a Xofigo single dose administration and should be reconsidered for the entire treatment cycle. Conclusions. The previous results are consistent with the literature. Their main advantage is the possibility to obtain immediate dose estimates, if the bone metastasis volume and its localized activity and time evolution are known. The experimental uncertainty is mainly related to volume and density of the metastatic tissue. https://doi.org/10.1016/j.ejmp.2018.04.341
333. A personalized acquisition protocol to optimize 18F-FDG PET/ CT whole-body imaging F. Zito a, A. D’Alessio b, A. Pira c, M.F. Bardo d, R. Benti d a
Medical Physics Unit, Fondazione IRCCS Ca Granda Ospedale Maggiore Policlinico, Milan, Italy b Medical Physics School, University of Milan, Italy c Radiology and Radioherapy Technologist School, University of Milan, Italy d Nuclear Medicine Unit, Fondazione IRCCS Ca Granda Ospedale Maggiore Policlinico, Milan, Italy Purpose. PET image quality degradation is encountered in overweight and obese patients even when administered activity is increased with body weight. For these cases is more appropriate to increase the acquisition time rather than administered activity. Aim of the work is to evaluate a metric related to patient body con-
stitution to optimize 18F-FDG PET/CT Whole-Body (PET-WB) acquisition procedure to guarantee accurate diagnosis with minimal radiation exposure of patients. Methods. PET-WB acquisitions were performed with the TruePoint Biograph scanner (Siemens) with 216 mm axial FOV; images were reconstructed with OSEM-3D with 2iterations/8subsets. Initial retrospective analysis was performed on 79 patients studied according to the PET-WB routine protocol: injection of 4.0 ± 0.6 MBq/kg, with a maximum of 500 MBq in obese subjects; acquisition duration of 2 min/bed and 3 min/bed respectively for body weight <100 kg and P100 kg. Signal to noise ratio (SNR) measured on liver region was taken as representative parameter of image quality. Diabetic patients and those with hepatic lesions were not included in the analysis. Measured SNR values were normalized to injected activity and acquisition duration (SNRn) and correlated with patient-specific parameters: height to weight ratio (HWR), body mass index (BMI), body surface area (BSA), lean body mass (LBM), fat free mass (FFM). A mathematical model was extrapolated from the parameter most correlated to SNRn values. The developed model was validated prospectively on others 66 patients. Results. Retrospective analysis showed a significant SNR decrease with increasing patient size. SNRn values fitted to patient-specific parameters showed the highest R2 (0.86) with HWR. Setting SNR reference value of 9, derived from an image quality deemed acceptable by clinicians for normal-weight patients, the HWR mathematical model allowed to personalize acquisition duration and keep constant image quality for different weight class. By fixing administered maximum activity to 380 MBq for obese subjects an increase of 30% acquisition time corresponded to 30% image SNR gain, with a 30% dose reduction to patient with respect EANM recommendations. Conclusions. The application of a model based on specific patient HWR allowed to improve SNR by personalizing acquisition duration without increasing patient dose exposure and to standardize PETWB procedure. https://doi.org/10.1016/j.ejmp.2018.04.342
334. Studio dosimetrico nelle SPECT/CT miocardiche di perfusione Dosimetric study in myocardial perfusion SPECT/CT G. Serreli a, C. Ghetti a, O. Ortenzia a, C. Cidda b, C. Lazzara b, L. Ruffini b a b
S.C. Fisica Sanitaria, AOU Parma, Italy S.C. Medicina Nucleare, AOU Parma, Italy
Purpose. We have evaluated, using a software tool for monitoring and tracking radiation dose, the radiation exposures in hybrid
Abstracts / Physica Medica 56 (2018) 133–278
myocardial perfusion imaging (MPI) before and after the optimization of the SPECT/CT acquisition protocol. Methods and materials. Examination data was collected from a SPECT/CT scanner Siemens Symbia T6 using Radimetrics version 2.6 (Bayer HealthCare, Whippany, NY). Data of MPI performed between 1st March 2016 and 1st March 2017 have been extracted from the DICOM header and Dose Report files produced by the scanner and stored in PACS. All analysis were made for exams in two days (TD) and in single day (SD). CTDIvol, DLP, SSDE, administered activity and Effective Dose were collected. A new optimized acquisition protocol was created changing CT parameters (mAs and pitch) and defining a new administered dose activity card with a reduction of the administered dose of about 18% for TD protocol and of only 4% for SD protocol because it was already well optimised. Examinations performed between 29th May 2017 and 30th November 2017 have been extracted and all dosimetric parameters were compared between old and new protocol. Results. The dose reduction for CT part of the MPI was approximately 52% for all the parameters analysed (CTDIvol, DLP, SSDE, Effective Dose) both for TD and SD protocol. The dose reduction for SPECT part was aligned with the reduction introduced in the new administered dose activity card. In MPI study we have achieved, with the new optimized protocol, a total dose reduction of about 30% in TD exams and of about 24% in SD exams (see table below). Conclusion. Using a software tool for monitoring and tracking radiation dose was possible to monitor, in real time, radiation exposure in SPECT/CT exams and analyze how to optimize the protocol to reduce effective dose to the patients.
265
MEGP collimator. The sensitivity was measured in air by varying activity, source–detector distance, and source diameter. Acquisition times were 10 min. Transmission curves were measured for attenuation and scatter correction with the pseudo-extrapolation number method. A real case has been simulated placing on the source a bone equivalent material and PMMA thickness simulating human condition. Results. The calibration factors is 63.4 cps/MBq. The table attenuation affects less than 11.5%. Sensitivity values for each head varies by 0.4% respect to the mean value with the source-detector distance and the activity. The effect of the partial volume decreases the calibration factor of the smaller source by 10%. The quantified activity in the real case differs by less than 15% respect to the measured activity. Conclusions. The calibration factor found is higher than the literature value (45.7 cps/MBq [2]). This result and the variation of the sensibility factor with source and acquisition setup stress the needed to characterize the system to perform a proper dosimetry estimation for any SPECT scanner. The error in determining the cumulated activity is less than 15%. Further studies including variation in source depth and acquisition time are needed to confirm these results including analysis in anthropomorphic phantom or human. References 1. Hindorf C. Quantitative imaging of 223Ra-chloride (Alpharadin) for targeted alpha-emitting radionuclide therapy of bone metastases. Nucl Med Commun 2012;33:726–32. 2. Pacilio M. Gamma camera calibrations for the Italian multicentre study for lesion dosimetry in 223Ra therapy of bone metastases. Physica Medica 2017;41:117–23. https://doi.org/10.1016/j.ejmp.2018.04.344
Acquisition Type
Old protocol TD Effective Dose (mSv)
New protocol TD Effective Dose (mSv)
Old protocol SD Effective Dose (mSv)
New protocol SD Effective Dose (mSv)
Rest Stress TC Total % Reduction
7.7 6.8 3.7 2 21.9
6.2 5.6 1.8 2 15.4
8 2.4 3.7 2 17.8
7.7 2.3 1.8 2 13.6
29.7%
23.6%
https://doi.org/10.1016/j.ejmp.2018.04.343
336. Validation of a methodology for SPECT/CT absolute quantification O. Ferrando a, A. Chimenz a, A. Ciarmiello b, F. Foppiano a 335. Uncertainty in quantification of cumulative activity in bone metastasis dosimetry with 223Ra R. Donnarumma a, M. Ghidini a, G. Toselli a, N. Prandini b, A. Franceschetto b, G. Guidi a, T. Costi a a Servizio di Fisica Medica, Azienda Ospedaliera-Universitaria di Modena, Modena, Italy b S.C di Medicina Nucleare, Dipartimento di Oncologia ed Ematologia, Azienda Ospedaliera-Universitaria di Modena, Modena, Italy
Purpose . Ra-223 therapy of prostate cancer bone metastases is being used to treat patients routinely. Accurate activity quantification through imaging is essential to calculate the absorbed dose in organs and sub-units in radiopharmaceutical therapy, enabling personalized absorbed dose-based treatment planning methodologies and more effective and optimal treatments. This work was aimed to estimate the error in quantifying cumulated activity in simulated case applying specific SPECT calibration procedure [1,2]. Methods. Calibrations with Ra-223 were performed with the SPECT/CT Infinia Hawkeye 4 GE (3/8-inch crystal) acquiring planar static images with double-peak (82 and 154 keV, 20% wide) and
a b
St. Andrea Hospital, Department of Medical Physics, La Spezia, Italy St. Andrea Hospital, Department of Nuclear Medicine, La Spezia, Italy
Purpose. To evaluate the activity quantification performance of our SPECT/CT scanner (SYMBIA T2 – SIEMENS) and to verify a methodology for absolute activity quantification. Methods. Quantitative SPECT/CT studies can be performed using the methodology proposed by Zeintl et al. [1]. The instrumentation consists of an uniform cylindrical phantom (5680 mL) and an IEC NEMA torso-phantom with hot sphere inserts. 99mTc was used to prepare the radioactive solutions. Different sphere-to-background ratio (RSB) were used (61:1, 44:1, 33:1, 10:1). Images were reconstructed using the proprietary OSEM 3D algorithm with resolution recovery (FLASH 3D, Siemens Healthcare), CT-based attenuation correction and energy window-based scatter correction. A system calibration factor (S) relating the count rate (cps) and the activity (mCi) contained in a tridimensional volume was determined together with the activity recovery coefficients. The phantom results were extended to 99mTc-MAA patient acquisitions for activity quantification in liver lesions. Lesions contouring was performed using the Volumetric Analysis Software (Siemens Healthcare).
Abstracts / Physica Medica 56 (2018) 133–278
morpho-functional assessment of activity distribution, a further step is needed to evaluate the local dose. Methods. Preliminary gamma-camera calibrations (sensitivity and transmission curves) for 223Ra were performed. After estimating the metastatic activity and volume through scintigraphic images, the target absorbed dose is given by the ratio between energy and mass. While the latter can be evaluated from the same images, the local energy depends on the physical characteristics of the emitted radiation and the cumulated activity. In this way, both the energy per Bq released by each radiation type and its fraction locally deposited can be calculated. Cumulated activity requires data on the Xofigo kinetics over time, available in literature. Results. Starting from the relative radiation emissions by 223Ra, 219Rn, 211Po, 211Bi and 207Tl the following MeV/Bq values were obtained: 26.3 alpha (95.33%), 1.0 beta (3.64%) and 0.3 X and gamma (1.03%). While charged particles energies are completely released to the biological mass, tissue absorption coefficients and target thickness must be considered for photons. By applying these criteria to a 118 cm3metastatic localization, a 0.35 MBq initial activity and a 4.73d effective half-life (see table and figures), the 6.7 Gy dose was obtained. This value concerns a Xofigo single dose administration and should be reconsidered for the entire treatment cycle. Conclusions. The previous results are consistent with the literature. Their main advantage is the possibility to obtain immediate dose estimates, if the bone metastasis volume and its localized activity and time evolution are known. The experimental uncertainty is mainly related to volume and density of the metastatic tissue. https://doi.org/10.1016/j.ejmp.2018.04.341
333. A personalized acquisition protocol to optimize 18F-FDG PET/ CT whole-body imaging F. Zito a, A. D’Alessio b, A. Pira c, M.F. Bardo d, R. Benti d a
Medical Physics Unit, Fondazione IRCCS Ca Granda Ospedale Maggiore Policlinico, Milan, Italy b Medical Physics School, University of Milan, Italy c Radiology and Radioherapy Technologist School, University of Milan, Italy d Nuclear Medicine Unit, Fondazione IRCCS Ca Granda Ospedale Maggiore Policlinico, Milan, Italy Purpose. PET image quality degradation is encountered in overweight and obese patients even when administered activity is increased with body weight. For these cases is more appropriate to increase the acquisition time rather than administered activity. Aim of the work is to evaluate a metric related to patient body con-
stitution to optimize 18F-FDG PET/CT Whole-Body (PET-WB) acquisition procedure to guarantee accurate diagnosis with minimal radiation exposure of patients. Methods. PET-WB acquisitions were performed with the TruePoint Biograph scanner (Siemens) with 216 mm axial FOV; images were reconstructed with OSEM-3D with 2iterations/8subsets. Initial retrospective analysis was performed on 79 patients studied according to the PET-WB routine protocol: injection of 4.0 ± 0.6 MBq/kg, with a maximum of 500 MBq in obese subjects; acquisition duration of 2 min/bed and 3 min/bed respectively for body weight <100 kg and P100 kg. Signal to noise ratio (SNR) measured on liver region was taken as representative parameter of image quality. Diabetic patients and those with hepatic lesions were not included in the analysis. Measured SNR values were normalized to injected activity and acquisition duration (SNRn) and correlated with patient-specific parameters: height to weight ratio (HWR), body mass index (BMI), body surface area (BSA), lean body mass (LBM), fat free mass (FFM). A mathematical model was extrapolated from the parameter most correlated to SNRn values. The developed model was validated prospectively on others 66 patients. Results. Retrospective analysis showed a significant SNR decrease with increasing patient size. SNRn values fitted to patient-specific parameters showed the highest R2 (0.86) with HWR. Setting SNR reference value of 9, derived from an image quality deemed acceptable by clinicians for normal-weight patients, the HWR mathematical model allowed to personalize acquisition duration and keep constant image quality for different weight class. By fixing administered maximum activity to 380 MBq for obese subjects an increase of 30% acquisition time corresponded to 30% image SNR gain, with a 30% dose reduction to patient with respect EANM recommendations. Conclusions. The application of a model based on specific patient HWR allowed to improve SNR by personalizing acquisition duration without increasing patient dose exposure and to standardize PETWB procedure. https://doi.org/10.1016/j.ejmp.2018.04.342
334. Studio dosimetrico nelle SPECT/CT miocardiche di perfusione Dosimetric study in myocardial perfusion SPECT/CT G. Serreli a, C. Ghetti a, O. Ortenzia a, C. Cidda b, C. Lazzara b, L. Ruffini b a b
S.C. Fisica Sanitaria, AOU Parma, Italy S.C. Medicina Nucleare, AOU Parma, Italy
Purpose. We have evaluated, using a software tool for monitoring and tracking radiation dose, the radiation exposures in hybrid
Abstracts / Physica Medica 56 (2018) 133–278
myocardial perfusion imaging (MPI) before and after the optimization of the SPECT/CT acquisition protocol. Methods and materials. Examination data was collected from a SPECT/CT scanner Siemens Symbia T6 using Radimetrics version 2.6 (Bayer HealthCare, Whippany, NY). Data of MPI performed between 1st March 2016 and 1st March 2017 have been extracted from the DICOM header and Dose Report files produced by the scanner and stored in PACS. All analysis were made for exams in two days (TD) and in single day (SD). CTDIvol, DLP, SSDE, administered activity and Effective Dose were collected. A new optimized acquisition protocol was created changing CT parameters (mAs and pitch) and defining a new administered dose activity card with a reduction of the administered dose of about 18% for TD protocol and of only 4% for SD protocol because it was already well optimised. Examinations performed between 29th May 2017 and 30th November 2017 have been extracted and all dosimetric parameters were compared between old and new protocol. Results. The dose reduction for CT part of the MPI was approximately 52% for all the parameters analysed (CTDIvol, DLP, SSDE, Effective Dose) both for TD and SD protocol. The dose reduction for SPECT part was aligned with the reduction introduced in the new administered dose activity card. In MPI study we have achieved, with the new optimized protocol, a total dose reduction of about 30% in TD exams and of about 24% in SD exams (see table below). Conclusion. Using a software tool for monitoring and tracking radiation dose was possible to monitor, in real time, radiation exposure in SPECT/CT exams and analyze how to optimize the protocol to reduce effective dose to the patients.
265
MEGP collimator. The sensitivity was measured in air by varying activity, source–detector distance, and source diameter. Acquisition times were 10 min. Transmission curves were measured for attenuation and scatter correction with the pseudo-extrapolation number method. A real case has been simulated placing on the source a bone equivalent material and PMMA thickness simulating human condition. Results. The calibration factors is 63.4 cps/MBq. The table attenuation affects less than 11.5%. Sensitivity values for each head varies by 0.4% respect to the mean value with the source-detector distance and the activity. The effect of the partial volume decreases the calibration factor of the smaller source by 10%. The quantified activity in the real case differs by less than 15% respect to the measured activity. Conclusions. The calibration factor found is higher than the literature value (45.7 cps/MBq [2]). This result and the variation of the sensibility factor with source and acquisition setup stress the needed to characterize the system to perform a proper dosimetry estimation for any SPECT scanner. The error in determining the cumulated activity is less than 15%. Further studies including variation in source depth and acquisition time are needed to confirm these results including analysis in anthropomorphic phantom or human. References 1. Hindorf C. Quantitative imaging of 223Ra-chloride (Alpharadin) for targeted alpha-emitting radionuclide therapy of bone metastases. Nucl Med Commun 2012;33:726–32. 2. Pacilio M. Gamma camera calibrations for the Italian multicentre study for lesion dosimetry in 223Ra therapy of bone metastases. Physica Medica 2017;41:117–23. https://doi.org/10.1016/j.ejmp.2018.04.344
Acquisition Type
Old protocol TD Effective Dose (mSv)
New protocol TD Effective Dose (mSv)
Old protocol SD Effective Dose (mSv)
New protocol SD Effective Dose (mSv)
Rest Stress TC Total % Reduction
7.7 6.8 3.7 2 21.9
6.2 5.6 1.8 2 15.4
8 2.4 3.7 2 17.8
7.7 2.3 1.8 2 13.6
29.7%
23.6%
https://doi.org/10.1016/j.ejmp.2018.04.343
336. Validation of a methodology for SPECT/CT absolute quantification O. Ferrando a, A. Chimenz a, A. Ciarmiello b, F. Foppiano a 335. Uncertainty in quantification of cumulative activity in bone metastasis dosimetry with 223Ra R. Donnarumma a, M. Ghidini a, G. Toselli a, N. Prandini b, A. Franceschetto b, G. Guidi a, T. Costi a a Servizio di Fisica Medica, Azienda Ospedaliera-Universitaria di Modena, Modena, Italy b S.C di Medicina Nucleare, Dipartimento di Oncologia ed Ematologia, Azienda Ospedaliera-Universitaria di Modena, Modena, Italy
Purpose . Ra-223 therapy of prostate cancer bone metastases is being used to treat patients routinely. Accurate activity quantification through imaging is essential to calculate the absorbed dose in organs and sub-units in radiopharmaceutical therapy, enabling personalized absorbed dose-based treatment planning methodologies and more effective and optimal treatments. This work was aimed to estimate the error in quantifying cumulated activity in simulated case applying specific SPECT calibration procedure [1,2]. Methods. Calibrations with Ra-223 were performed with the SPECT/CT Infinia Hawkeye 4 GE (3/8-inch crystal) acquiring planar static images with double-peak (82 and 154 keV, 20% wide) and
a b
St. Andrea Hospital, Department of Medical Physics, La Spezia, Italy St. Andrea Hospital, Department of Nuclear Medicine, La Spezia, Italy
Purpose. To evaluate the activity quantification performance of our SPECT/CT scanner (SYMBIA T2 – SIEMENS) and to verify a methodology for absolute activity quantification. Methods. Quantitative SPECT/CT studies can be performed using the methodology proposed by Zeintl et al. [1]. The instrumentation consists of an uniform cylindrical phantom (5680 mL) and an IEC NEMA torso-phantom with hot sphere inserts. 99mTc was used to prepare the radioactive solutions. Different sphere-to-background ratio (RSB) were used (61:1, 44:1, 33:1, 10:1). Images were reconstructed using the proprietary OSEM 3D algorithm with resolution recovery (FLASH 3D, Siemens Healthcare), CT-based attenuation correction and energy window-based scatter correction. A system calibration factor (S) relating the count rate (cps) and the activity (mCi) contained in a tridimensional volume was determined together with the activity recovery coefficients. The phantom results were extended to 99mTc-MAA patient acquisitions for activity quantification in liver lesions. Lesions contouring was performed using the Volumetric Analysis Software (Siemens Healthcare).