- Email: [email protected]
Monte Carlo and clinical study of the impact of attenuation and scatter corrections on prospective 3D dosimetry for radioembolization with 90Y microspheres
Abstracts/Physica Medica 32 (2016) e97–e115
Introduction: PET/CT imaging allows to obtain brain metabolic and functional information that is fundamental for pre and post-therapy lesion assessment. 11C-labeled methionine (MET) is the main radiotracer used to study this kind of lesion. Therefore it becomes necessary to optimize the clinical protocol for the use of this radiotracer. The purpose of this study was to optimize the acquisition time. Materials and Methods: This study considered 15 patients who underwent an MET-PET/CT examination performed on a Discovery 690 Scanner (GE). The standard protocol is: acquisition time, 15′, and injected activity 550 MBq. Using the list mode function, the exams were reconstructed with three different acquisition times: 5′, 7′30″ and 10′. The mean ROI counter per pixel, placed in an internal lesion region (L) and also in a reference normal region (N), and the Volume of each lesion were evaluated using home made DICOM analysis software for all acquisition time. The data at 5′, 7′30″ and 10′ were compared with the standard one. Results: The assessment of L/N ratio of the three PET image reconstructions allows to identify the one that better matches the standard reconstruction. The 10′ image reconstruction was the best to obtain this result. In case of lesions with dimension smaller than 2 cm3, the lesion volume measured in standard and 10′ reconstructions differed about 6%. The 10′ reconstructions were evaluated by the nuclear physician team and no substantial differences with standard reconstruction were noticed. Conclusions: Our study shows that, in our system, it is possible to reduce the acquisition time for MET-PET/CT scan to investigate brain metabolism, without affecting the clinical quality of images. This means that a reduction of the dose to the patient can be carried out without interfering with the normal execution of the exam. In this way a better radioprotection for the patient is achieved, with identical reliability of images for diagnostic use. http://dx.doi.org/10.1016/j.ejmp.2016.01.369 C.364 GAMMA TOMOSYNTHESIS FOR MOLECULAR IMAGING M. Longo *,a, R. Pellegrini b,c, M.N. Cinti b,c, V. Frantellizzi d, G. De Vincentis d, R. Pani c,e. a Post Graduate School of Medical Physics, Sapienza University of Rome, Rome, Italy; b Department of Molecular Medicine, Sapienza University of Rome, Rome, Italy; c INFN Roma I Section, Rome, Italy; d Department of Radiological Sciences, Oncology and Anatomical Pathology, Sapienza University of Rome, Rome, Italy; e Department of Sciences and Medical and Surgical Biotechnologies, Sapienza University of Rome, Rome, Italy Introduction: It is well known that without the ability to detect small lesions, indicative of early stage disease, molecular imaging technique has limited clinical utility. Commonly available Anger cameras, which are large, bulky and designed for general-purpose imaging, are not ideal for detecting lesion smaller than 1 cm. To overcome these limitations, we propose a gamma tomosynthesis method based on a slant collimation system that, complemented to a conventional gamma camera, performs high resolution three-dimensional imaging. Materials and Methods: The slant hole collimation system dedicated to gamma tomosynthesis is characterized by the capability of tilting its holes according to variable angles. This system allows to acquire a set of planar images at different angles, which are then reconstructed through the Shift And Add (SAA) method to obtain the three-dimensional distribution of a radioactive tracer. This technique was validated by experimental measurements with dedicated phantoms, using our collimation system on the gamma camera GE Millennium. A phantom is realized using a cylindrical container with a background activity and two spheres filled with 99mTc, with different uptakes, representing the hot spots. Moreover, the Mini Defrise phantom was used to examine how well the tomosynthesis technique preserves axial resolutions. Results: The system allows to reach sub-centimeters coronal and sagittal spatial resolutions, while the spatial resolution becomes worst in the axial direction. This latter sub-optimal response could be solved by performing the SAA reconstruction without small angle projections, even if this implies a reduction of contrast and signal to noise ratio. Conclusion: Different from currently used SPECT, a conventional gamma camera equipped with this slant collimation system could be located in a fixed position at the minimum distance from the patient, thus
e107
improving detection, localization and characterization of sub-centimeter lesions. http://dx.doi.org/10.1016/j.ejmp.2016.01.370 C.365 MONTE CARLO AND CLINICAL STUDY OF THE IMPACT OF ATTENUATION AND SCATTER CORRECTIONS ON PROSPECTIVE 3D DOSIMETRY FOR RADIOEMBOLIZATION WITH 90Y MICROSPHERES M. Pacilio a, L. Lorenzon *,b, M. Ferrari c, C. Chiesa d, F. Botta c, M. Mira e, D. Becci b, L.A. Torres f, M.C. Perez f, C. Basile a, M. Ljungberg g, R. Pani h, M. Cremonesi c. a Department of Medical Physics, Azienda Ospedaliera San Camillo Forlanini, Rome, Italy; b Postgraduate School of Medical Physics, Sapienza University of Rome, Rome, Italy; c Department of Medical Physics, Istituto Europeo di Oncologia, Milan, Italy; d Department of Nuclear Medicine, Istituto Nazionale Tumori IRCCS Foundation, Milan, Italy; e Post graduate Health Physics School, University of Milan, Milan, Italy; f Department of Nuclear Medicine, Clinical Research Division of the Center of Isotopes (DIC-CENTIS), Havana, Cuba; g Department of Medical Radiation Physics, University of Lund, Lund, Sweden; h Department of Molecular Medicine, Sapienza University of Rome, Rome, Italy Introduction: The aim of this study was to evaluate the impact of the absence of attenuation or scatter corrections in 99mTc-MAA-SPECT images in radioembolization treatment planning. Materials and Methods: Monte Carlo simulations were performed for three anthropomorphic phantoms with different activity distributions in the liver. Liver motion due to breathing was also simulated. 36 patients with hepatocellular carcinoma or liver metastasis were considered. Images were reconstructed by OSEM algorithm, switching on and off attenuation (AC) and scatter (SC) correction. 3D dosimetry was performed with voxel S value approach, using a relative calibration method. Cumulative dose–volume histograms in Tumoral Liver (TL) and Healthy Parenchyma (HP) were compared, assessing differences for D95%, D70% and D50%. For simulated cases, the dose image derived from the input activity map was the Gold Standard (GS). For clinical cases, the dose map obtained using AC and SC was the reference. Results: For simulated cases, differences vs. GS are severe. Modest compensation derives from AC and SC. For TL, dosimetric indicators are underestimated in most cases. For HP, differences are distributed around zero and show a reduced spread considering the D50% parameter. Patient breathing worsens the differences, in particular for TL. In the clinical cases, the absence of AC (not available in all centers) affects lesion dosimetry more importantly than SC (always feasible), but it is less critical for HP, which is the main focus of the planning. Conclusions: All corrections would be needed to improve dosimetric accuracy. For TL, more efforts are required to obtain an accurate dosimetry. HP dosimetry seems to be less critical and D50% is a more reliable dosimetric indicator. Dosimetric planning without CT based AC, although approximated, is preferable than adopting non dosimetric methods. http://dx.doi.org/10.1016/j.ejmp.2016.01.371 C.366 ACCURATE MEASUREMENTS OF LOW ACTIVITY FOR CALIBRATION OF A RIA GAMMA COUNTER USED IN RED MARROW DOSIMETRY L. Lorenzon *,a, S. Donatiello b, V. Cannatà b, M.C. Garganese c, G. Giannone d, C. Orlandi b, M. Pacilio e, E. Genovese b. a Postgraduate School of Medical Physics, Sapienza University of Rome, Rome, Italy; b Enterprise Risk Manager/Medical Physics, Bambino Gesù Children’s Hospital, IRCCS, Rome, Italy; c Department of Nuclear Medicine, Bambino Gesù Children’s Hospital, IRCCS, Rome, Italy; d Department of Laboratories, Bambino Gesù Children’s Hospital, IRCCS, Rome, Italy; e Department of Medical Physics, Azienda Ospedaliera San Camillo Forlanini, Rome, Italy Introduction: In radionuclide therapy, a RIA gamma counter can be used routinely to measure the activity concentration in the blood for red marrow dosimetry, essential to control haematological toxicity. Calibration of a gamma counter, due to its high sensitivity, has to be performed with sources of low and known activity. The aim of this work was to perform the calibration in terms of activity-counts of a RIA gamma counter, used for 131-I blood sample measurements, by implementing the weighing method for accurate measurements of low activity calibration sources.
Introduction: PET/CT imaging allows to obtain brain metabolic and functional information that is fundamental for pre and post-therapy lesion assessment. 11C-labeled methionine (MET) is the main radiotracer used to study this kind of lesion. Therefore it becomes necessary to optimize the clinical protocol for the use of this radiotracer. The purpose of this study was to optimize the acquisition time. Materials and Methods: This study considered 15 patients who underwent an MET-PET/CT examination performed on a Discovery 690 Scanner (GE). The standard protocol is: acquisition time, 15′, and injected activity 550 MBq. Using the list mode function, the exams were reconstructed with three different acquisition times: 5′, 7′30″ and 10′. The mean ROI counter per pixel, placed in an internal lesion region (L) and also in a reference normal region (N), and the Volume of each lesion were evaluated using home made DICOM analysis software for all acquisition time. The data at 5′, 7′30″ and 10′ were compared with the standard one. Results: The assessment of L/N ratio of the three PET image reconstructions allows to identify the one that better matches the standard reconstruction. The 10′ image reconstruction was the best to obtain this result. In case of lesions with dimension smaller than 2 cm3, the lesion volume measured in standard and 10′ reconstructions differed about 6%. The 10′ reconstructions were evaluated by the nuclear physician team and no substantial differences with standard reconstruction were noticed. Conclusions: Our study shows that, in our system, it is possible to reduce the acquisition time for MET-PET/CT scan to investigate brain metabolism, without affecting the clinical quality of images. This means that a reduction of the dose to the patient can be carried out without interfering with the normal execution of the exam. In this way a better radioprotection for the patient is achieved, with identical reliability of images for diagnostic use. http://dx.doi.org/10.1016/j.ejmp.2016.01.369 C.364 GAMMA TOMOSYNTHESIS FOR MOLECULAR IMAGING M. Longo *,a, R. Pellegrini b,c, M.N. Cinti b,c, V. Frantellizzi d, G. De Vincentis d, R. Pani c,e. a Post Graduate School of Medical Physics, Sapienza University of Rome, Rome, Italy; b Department of Molecular Medicine, Sapienza University of Rome, Rome, Italy; c INFN Roma I Section, Rome, Italy; d Department of Radiological Sciences, Oncology and Anatomical Pathology, Sapienza University of Rome, Rome, Italy; e Department of Sciences and Medical and Surgical Biotechnologies, Sapienza University of Rome, Rome, Italy Introduction: It is well known that without the ability to detect small lesions, indicative of early stage disease, molecular imaging technique has limited clinical utility. Commonly available Anger cameras, which are large, bulky and designed for general-purpose imaging, are not ideal for detecting lesion smaller than 1 cm. To overcome these limitations, we propose a gamma tomosynthesis method based on a slant collimation system that, complemented to a conventional gamma camera, performs high resolution three-dimensional imaging. Materials and Methods: The slant hole collimation system dedicated to gamma tomosynthesis is characterized by the capability of tilting its holes according to variable angles. This system allows to acquire a set of planar images at different angles, which are then reconstructed through the Shift And Add (SAA) method to obtain the three-dimensional distribution of a radioactive tracer. This technique was validated by experimental measurements with dedicated phantoms, using our collimation system on the gamma camera GE Millennium. A phantom is realized using a cylindrical container with a background activity and two spheres filled with 99mTc, with different uptakes, representing the hot spots. Moreover, the Mini Defrise phantom was used to examine how well the tomosynthesis technique preserves axial resolutions. Results: The system allows to reach sub-centimeters coronal and sagittal spatial resolutions, while the spatial resolution becomes worst in the axial direction. This latter sub-optimal response could be solved by performing the SAA reconstruction without small angle projections, even if this implies a reduction of contrast and signal to noise ratio. Conclusion: Different from currently used SPECT, a conventional gamma camera equipped with this slant collimation system could be located in a fixed position at the minimum distance from the patient, thus
e107
improving detection, localization and characterization of sub-centimeter lesions. http://dx.doi.org/10.1016/j.ejmp.2016.01.370 C.365 MONTE CARLO AND CLINICAL STUDY OF THE IMPACT OF ATTENUATION AND SCATTER CORRECTIONS ON PROSPECTIVE 3D DOSIMETRY FOR RADIOEMBOLIZATION WITH 90Y MICROSPHERES M. Pacilio a, L. Lorenzon *,b, M. Ferrari c, C. Chiesa d, F. Botta c, M. Mira e, D. Becci b, L.A. Torres f, M.C. Perez f, C. Basile a, M. Ljungberg g, R. Pani h, M. Cremonesi c. a Department of Medical Physics, Azienda Ospedaliera San Camillo Forlanini, Rome, Italy; b Postgraduate School of Medical Physics, Sapienza University of Rome, Rome, Italy; c Department of Medical Physics, Istituto Europeo di Oncologia, Milan, Italy; d Department of Nuclear Medicine, Istituto Nazionale Tumori IRCCS Foundation, Milan, Italy; e Post graduate Health Physics School, University of Milan, Milan, Italy; f Department of Nuclear Medicine, Clinical Research Division of the Center of Isotopes (DIC-CENTIS), Havana, Cuba; g Department of Medical Radiation Physics, University of Lund, Lund, Sweden; h Department of Molecular Medicine, Sapienza University of Rome, Rome, Italy Introduction: The aim of this study was to evaluate the impact of the absence of attenuation or scatter corrections in 99mTc-MAA-SPECT images in radioembolization treatment planning. Materials and Methods: Monte Carlo simulations were performed for three anthropomorphic phantoms with different activity distributions in the liver. Liver motion due to breathing was also simulated. 36 patients with hepatocellular carcinoma or liver metastasis were considered. Images were reconstructed by OSEM algorithm, switching on and off attenuation (AC) and scatter (SC) correction. 3D dosimetry was performed with voxel S value approach, using a relative calibration method. Cumulative dose–volume histograms in Tumoral Liver (TL) and Healthy Parenchyma (HP) were compared, assessing differences for D95%, D70% and D50%. For simulated cases, the dose image derived from the input activity map was the Gold Standard (GS). For clinical cases, the dose map obtained using AC and SC was the reference. Results: For simulated cases, differences vs. GS are severe. Modest compensation derives from AC and SC. For TL, dosimetric indicators are underestimated in most cases. For HP, differences are distributed around zero and show a reduced spread considering the D50% parameter. Patient breathing worsens the differences, in particular for TL. In the clinical cases, the absence of AC (not available in all centers) affects lesion dosimetry more importantly than SC (always feasible), but it is less critical for HP, which is the main focus of the planning. Conclusions: All corrections would be needed to improve dosimetric accuracy. For TL, more efforts are required to obtain an accurate dosimetry. HP dosimetry seems to be less critical and D50% is a more reliable dosimetric indicator. Dosimetric planning without CT based AC, although approximated, is preferable than adopting non dosimetric methods. http://dx.doi.org/10.1016/j.ejmp.2016.01.371 C.366 ACCURATE MEASUREMENTS OF LOW ACTIVITY FOR CALIBRATION OF A RIA GAMMA COUNTER USED IN RED MARROW DOSIMETRY L. Lorenzon *,a, S. Donatiello b, V. Cannatà b, M.C. Garganese c, G. Giannone d, C. Orlandi b, M. Pacilio e, E. Genovese b. a Postgraduate School of Medical Physics, Sapienza University of Rome, Rome, Italy; b Enterprise Risk Manager/Medical Physics, Bambino Gesù Children’s Hospital, IRCCS, Rome, Italy; c Department of Nuclear Medicine, Bambino Gesù Children’s Hospital, IRCCS, Rome, Italy; d Department of Laboratories, Bambino Gesù Children’s Hospital, IRCCS, Rome, Italy; e Department of Medical Physics, Azienda Ospedaliera San Camillo Forlanini, Rome, Italy Introduction: In radionuclide therapy, a RIA gamma counter can be used routinely to measure the activity concentration in the blood for red marrow dosimetry, essential to control haematological toxicity. Calibration of a gamma counter, due to its high sensitivity, has to be performed with sources of low and known activity. The aim of this work was to perform the calibration in terms of activity-counts of a RIA gamma counter, used for 131-I blood sample measurements, by implementing the weighing method for accurate measurements of low activity calibration sources.