Effective dose estimate in PET-CT examinations

Abstracts/Physica Medica 32 (2016) e97–e115

fix the maximum value of contamination accepted. In this work we propose a procedure to assess the radionuclide purity of [18F]FDG samples for routine quality controls by using gamma ray spectrometry. Materials and Methods: 18-fluorine is produced through proton irradiation of a small volume of 18-oxygen enriched water in a 9 MeV cyclotron and then transferred to a synthesis module for the production of [18F]FDG to be injected. Gamma rays emitted by samples of the radiopharmaceutical are acquired by an HPGe detector shielded by lead from atmospheric background radiation; gamma spectra are analyzed with a software that associates the peaks in the spectrum to radionuclides included in a library user defined and uses efficiency and energy calibrations to calculate the activities. Minimum Detectable Activities (MDA) for the nuclides in the library are also provided. Results: Base on literature evidence, a library was developed taking into account all possible contaminants in [18F]FDG routine production of our center with a mean life compatible with timing involved in the detection. Spectrum acquisition duration was evaluated considering the minimum concentration to be detected for a long-life contaminant. Cross verifications were also used to identify the origin of the peaks in the spectra. Radionuclide purity was then evaluated as the ratio between the sum of detected activities (related to release time) and the total activity actually measured at the release time. The sum of MDAs and detected activities was finally used as an estimate of the maximum activity due to all contaminants. Conclusions: The procedure can be used in the routine for radionuclide purity assessment of FDG and can be extended to other radiopharmaceutical. The proposed method supplies instruments to verify the reliability of obtained results. http://dx.doi.org/10.1016/j.ejmp.2016.01.389 C.384 DIFFERENT POLAR-MAP PATTERNS USING THE NOVEL TECHNOLOGY FOR MYOCARDIAL PERFUSION IMAGING (MPI) C. Scabbio *,a, O. Zoccarato b, C. Marcassa b, D. Lizio c, L. Leva c, G. Lucignani a, A. Savi d, R. Matheoud c, M. Lecchi a, M. Brambilla c. a Department of Health Sciences, University of Milan and Nuclear Medicine Unit, San Paolo Hospital, Milan, Italy; b Unit of Nuclear Medicine and Department of Cardiology, S. Maugeri Foundation, IRCCS, Scientific Institute of Veruno, Veruno (NO), Italy; c Departments of Medical Physics and Nuclear Medicine, University Hospital Maggiore della Carità, Novara, Italy; d Unit of Nuclear Medicine, San Raffaele Hospital of Milan (IRCCS), Milan, Italy Introduction: Iterative algorithms with resolution recovery (IRRs), innovative collimators and dedicated cameras with CZT detectors are now available in MPI. Our aim was to evaluate the impact of this novel technology on the uniformity of normal myocardial uptake in the polar-map representation, over a wide range of acquired count statistics, and with and without the attenuation and scatter corrections (SCAC). Materials and Methods: A phantom study was performed and considered twenty-one scanner/software combinations and reconstruction methods: 4 conventional gamma-cameras with filtered-back-projection (FBP) or IRR, with or without AC; a Symbia–IQ (Siemens) and a D530c (General Electric), with or without AC; and a D-SPECT (Spectrum Dynamics). Different count statistics were considered up to a quarter of the reference (6 × 106 counts in the left-ventricular) for the conventional gammacameras and up to one-twelfth for the advanced scanners. Using the 17segment polar-map, the regional and vascular segmental uptakes, the coefficient of variation (COV) among the segmental uptakes and the anterior/ inferior (ANT/INF) ratio were calculated. Results: The normal polar-map pattern did not depend on the selected count statistics. Reconstruction method and scanner/software combination (p < 0.0001) were all main effects with a statistically significant impact on normal myocardial uptake. A significant increase in the segmental uptakes was found from IRR to IRR + SCAC (78.0 ± 13.5% vs 86.1 ± 9.4%; p < 0.0001). COV was significantly lower for D-SPECT (10.1 ± 0.5%) and after SCAC both for conventional (9.9 ± 3.0%) and advanced systems (8.9 ± 1.7%). The ANT/ INF ratio was above 1 for IRR (1.12 ± 0.07), while fell below 1 for IRR + SCAC (0.97 ± 0.05). Conclusions: Different normal polar-map patterns were found in MPI. However, for the same scanner/software combination and reconstruction

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method, low-dose or short-time studies could be performed using the same normality database of the reference protocol. http://dx.doi.org/10.1016/j.ejmp.2016.01.390

C.385 CHARACTERIZATION OF A PET SCANNER FOR IMAGING WITH 68GA G. Serreli *,a, O. Ortenzia a, L. Ruffini b, C. Ghetti a. a Servizio di Fisica Sanitaria, AOU Parma, Parma, Italy; b S.C. Medicina Nucleare, AOU Parma, Parma, Italy Aim: The aim of this study is the characterization of the new PET scanner GE Discovery IQ for imaging with 68Ga. 68Ga radionuclide has great interest in PET imaging because somatostatin receptor-based imaging with 68Ga-labeled radioligands is considered superior in detection of NET primary tumors and metastases on the other standard imaging techniques. Moreover it is possible to provide 68Ga, with a 68Ge/68Ga generator, on demand in sites without a cyclotron. Methods and Materials: NEMA NU-2-2007 tests were performed with 68Ga for Discovery IQ to measure spatial resolution, sensitivity and PET image quality (IQ). IQ test was made with NEMA IEC Body phantom filling the fourth smallest spheres. The hot-spheres/background concentration ratio was 4:1. Data were corrected for attenuation, scatter, and random coincidences, and the images were reconstructed with VPHD and the new QC algorithm. We have evaluated the correctness of SUV calculation, acquiring a 68Ga uniformity phantom twice: first, acquisition with the 68Ga WCC calibration and, second, using 18F WCC calibration. Results: The spatial resolution, respectively radial, tangential, axial at 1 cm and at 10 cm, was 3.82, 4.67, 4.91 mm and 5.89, 4.77, 5.03 mm. The results using 18F were 3.8, 4.7, 4.81, 5.81, 4.24, and 5.79 mm. Sensitivity at the center and at 10 cm off-center was 26.70 and 28.10 cps/ kBq. 18F results were 22.4 and 20 cps/kBq. Contrast recovery coefficients (CRC) for spheres were 37.6% (1.00 mm), 43.90% (1.30 mm), 62.20% (1.70 mm), 69.00% (2.20 mm), 70.80% (2.80 mm) and 74.40% (3.70 mm). 18F results were 36.50%, 58.40%, 68.20%, 67.60%, 72.40% and 76.10%. RE over the lung insert was 18.4% with 68Ga and 17.60% with 18F. Furthermore it was verified that the evaluation of SUV is correct within the 10% using 18F WCC calibration even for 68Ga exams. Conclusions: The performances of Discovery IQ with 68Ga are fully comparable to those with the 18F. In addition, in clinical routine it is not necessary to use a dedicated 68Ga WCC calibration. http://dx.doi.org/10.1016/j.ejmp.2016.01.391

C.386 EFFECTIVE DOSE ESTIMATE IN PET-CT EXAMINATIONS M. Sireus *,a, O. Ortenzia b, F. Palleri b, G. Serreli b, L. Ruffini c, C. Ghetti b. a Università degli Studi di Cagliari, Cagliari, Italy; b Servizio di Fisica Sanitaria, AOU Parma, Parma, Italy; c S.C. Medicina Nucleare, AOU Parma, Parma, Italy Introduction: The recent Directive EURATOM 2013/59, which will be implemented by member states within February 2018, introduces the need to communicate dosimetric data to the patient. The purpose of this study is to assess the CTDIvol, DLP and administered activity in PET-CT examinations; we have also evaluated the effective dose for the whole procedure in order to verify that also in hybrid imaging the ALARA principle is respected. Materials and Methods: The study was performed in the Nuclear Medicine Dept of Parma Hospital using a GE Discovery-ST PET-CT. We retrospectively evaluated the mean value of Effective Dose for a sample of 40 patients (20 men and 20 women) who underwent F-18 Total Body examination. Dosimetric data (CTDIvol, DLP and injected activity) were manually extrapolated from DICOM header. We calculated CT contribution to the Effective Dose using the ImPACT CT Patient Dosimetry Calculator and PET contribution to the Effective Dose using activity/dose conversion coefficients published in the EJNMMI Physics (2014) using different values for men and women. Results: The mean CTDIvol and administered activity were 2.1 mGy and 3.7 MBq/kg respectively. The mean Effective Dose was 7.8 ± 1.5 mSv for men

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(3.3 ± 1.3 mSv for CT and 4.5 ± 0.3 mSv for PET contribution) and 7.3 ± 1.5 mSv for women (3.2 ± 1.4 mSv for CT and 4.1 ± 0.2 mSv for PET contribution). The mean Effective Dose was 7.5 ± 1.5 mSv for all patients (3.2 ± 1.3 mSv for CT and 4.3 ± 0.3 mSv for PET contribution). These values were then compared with the published literature (Tonkopi, AJR 2013). Conclusions: Our results were in good agreement with the published literature and were presented to physicians and technicians of the Nuclear Medicine Dept. We have recently installed a new PET-CT (GE DiscoveryIQ) and we will evaluate the effective dose obtained with the new scanner. http://dx.doi.org/10.1016/j.ejmp.2016.01.392

C.387 EVALUATION OF COMMERCIAL SOFTWARE PERFORMANCE IN RETRIEVING INFORMATION FROM MERGED SPECT AND CT IMAGES: A PHANTOM STUDY C. Giliberti a, S. Strolin b, S. Ungania b, A. Cacciatore b, A. Soriani b, G. Iaccarino b, M. D’Andrea b, L. Strigari *,b. a INAIL Dipartimento Innovazioni Tecnologiche e Sicurezza degli Impianti, Prodotti e Insediamenti Antropici, Rome, Italy; b Laboratory of Medical Physics and Expert Systems, Regina Elena National Cancer Institute, Rome, Italy Introduction: Tumor displacement in patients with liver metastasis may be registered by multimodal imaging. The aim of this study was to investigate the performance of commercial image fusion software in measuring the activity and the volumes of inserts simulating liver lesions at different positions in a phantom. Materials and Methods: A novel experimental setup has been designed using Jaszczak phantom and fillable plastic balloons. A solution with a contrast agent at 1% and a concentration of 0.42 MBq/mL were prepared. Two balloons were filled with the solution and fixed to the phantom in order to simulate liver lesions of equal size at different phantom position. All acquisitions were performed using a three-head 3/8’’ (9.5 mm) NaI crystal Philips IRIX gamma-camera. Two iterative algorithms were used to reconstruct SPECT images: the maximum likelihood expectation maximization (MLEM) and the ordered subsets expectation maximization (OSEM). The number of iterations was 10, 20, 50 and 4, 10, 20 for MLEM and OSEM respectively. Using the MIMvistaTM software, several regions of interest (ROIs) were generated on both SPECT and CT images with a threshold method at different percentages of maximum activity values. Image based recovered data have been compared with the expected activity to find the most appropriate threshold to recover the activity values under controlled experimental conditions. Results: MLEM algorithm with 20 iterations was the most accurate reconstruction method with a 1% of difference between expected and recovered activity. A 30% threshold gave the smallest volume difference between the two ROIs and a measured value closest to the true volume measured on the CT. Conclusion: This experimental setup can be used to identify appropriate thresholds for hepatic lesions when considering internal lesion movements using multimodal imaging. http://dx.doi.org/10.1016/j.ejmp.2016.01.393

C.388 ABSOLUTE GAMMA CAMERA CALIBRATION FOR QUANTITATIVE SPECT IMAGING WITH 177LU M. D’Arienzo a,b, M.L. Cozzella a, A. Fazio a, S. Ungania *,c,d, M. Cazzato c, G. Iaccarino c, M. D’Andrea c, L. Strigari c, A. Fenwick e, M. Cox e, L. Johansson e, P. De Felice a. a ENEA, National Institute of Ionizing Radiation Metrology, Rome, Italy; b Department of Anatomical, Histological, Forensic Medicine and Orthopedic Sciences, La Sapienza University, Rome, Italy; c Laboratory of Medical Physics and Expert Systems, Regina Elena National Cancer Institute, Rome, Italy; d Medical Physics Specialization School, Faculty of Medicine, Tor Vergata University, Rome, Italy; e National Physical Laboratory (NPL), Teddington, UK Introduction: Gamma camera calibration in molecular radiotherapy is currently performed either in-air or in-water using a source with a known amount of activity. However, at present there are no standard protocols or

any established methods for calibration and verification of system performance. The aim of this work was to develop an approach to gamma camera calibration for absolute quantification of 177Lu. Materials and Methods: Calibration studies were performed on a Philips IRIX and AXIS gamma camera using four reference geometries: a point source in air, a 16 mL Jaszczak sphere surrounded by non-radioactive water, a 16 mL Jaszczak sphere in air and a 20 cm diameter cylinder filled with 177LuCl. Acquisitions were corrected both for scatter and attenuation. We validated our method using an anthropomorphic phantom provided with liver cavity filled with 177LuCl. Results: Acquisitions performed with the IRIX gamma camera provided better results, with agreements within 5% for all geometries for acquisitions at 208 keV. The Jaszczak sphere in water provided sensitivity values capable of recovering the activity in anthropomorphic geometry within 1% for the 208 keV peak, for both gamma cameras. The point source provided the poorest results, most likely because scatter and attenuation correction are not incorporated in the calibration factor. For both systems the activity in anthropomorphic geometry was recovered with an agreement in the range −11.6%/+7.3% at 208 keV. Conclusions: Scatter and attenuation play a major role at 113 keV and are likely to hinder an accurate quantification. Acquisitions at 208 keV are therefore recommended in the clinical practice. Preliminary results suggest that the gamma camera calibration factor can be determined with a standard uncertainty below 3% if activity measurements are performed with equipment traceable to primary standards, accurate volume measurements are made, and a favourable chemistry is used during the experimental activity. http://dx.doi.org/10.1016/j.ejmp.2016.01.394

C.389 IMPACT OF ATTENUATION AND SCATTER CORRECTION IN PREVISIONAL DOSIMETRY BASED ON SPECT-CT IMAGES FOR RADIOEMBOLIZATION OF LIVER LESIONS WITH 90Y MICROSPHERES S. Valzano *,a, C. Cutaia a, E. Richetta a, M. Pasquino a, R.E. Pellerito b, M. Stasi a. a Medical Physics Unit, AO Ordine Mauriziano, Turin, Italy; b Nuclear Medicine Unit, AO Ordine Mauriziano, Turin, Italy Introduction: Previsional dosimetry of hepatic radioembolization with 90Y microsphere is performed with 99mTc-MAA acquisitions in order to avoid shunts and to estimate dose to lesions and normal liver. The accuracy of the dose calculation depends both on the dosimetric method and on the image reconstruction algorithms. The aim of this study was to compare doses calculated with MIRD and voxel methods based on SPECT-CT images with or without attenuation and scatter corrections. Materials and Methods: 10 HCC patients were treated with 90Y-resin spheres (1.4 ± 0.4 GBq). For previsional dosimetry 99mTc-MAA SPECT-CT (SIEMENS Symbia Intevo, LEHR, 128 × 128, 60 views, 18 s/view) acquisitions were performed. Images were reconstructed with iterative (IT) algorithm (Flash3D, 8i8s) with attenuation and scatter corrections and with FBP algorithm without any correction. Lesion (T) and normal liver (NL) doses were estimated from SPECT-CT images with MIRD compartmental method (VOI counts, isocontour) and with a homemade voxel dosimetry MatLab code. T and NL volumes were obtained on IT and FBP reconstructions and employed for the two dosimetric approaches. MIRD and voxel mean doses to T and NL were calculated on IT and FBP reconstructed images: absolute and percentage comparisons were performed. Results: MIRD compartmental T mean doses were 205 Gy for IT and 224 Gy for FBP; NL mean doses were 57 Gy (IT) and 67 Gy (FBP). Mean T doses, obtained with voxel method, were 167 Gy (IT) and 170 Gy (FBP); NL mean doses were 48 Gy (IT) and 54 Gy (FBP). Using MIRD compartmental method, the mean percent dose differences (±sd), estimated on IT and FBP images, were 11% (±35%) for T and 13% (±34%) for NL. For voxel dosimetry method, the mean percent dose differences (±sd), estimated on reconstructed images, were 2% (±22%) and 7% (±27%) for T and NL respectively. Conclusions: SPECT-CT reconstruction algorithms and attenuation and scatter corrections could significantly affect dose calculation and must be considered in different dosimetric approaches. http://dx.doi.org/10.1016/j.ejmp.2016.01.395