Leda Lorenzon - Academia.edu (original) (raw)

Papers by Leda Lorenzon

European Radiology Experimental

In prostate cancer (PCa), the use of new radiopharmaceuticals has improved the accuracy of diagno... more In prostate cancer (PCa), the use of new radiopharmaceuticals has improved the accuracy of diagnosis and staging, refined surveillance strategies, and introduced specific and personalized radioreceptor therapies. Nuclear medicine, therefore, holds great promise for improving the quality of life of PCa patients, through managing and processing a vast amount of molecular imaging data and beyond, using a multi-omics approach and improving patients’ risk-stratification for tailored medicine. Artificial intelligence (AI) and radiomics may allow clinicians to improve the overall efficiency and accuracy of using these “big data” in both the diagnostic and theragnostic field: from technical aspects (such as semi-automatization of tumor segmentation, image reconstruction, and interpretation) to clinical outcomes, improving a deeper understanding of the molecular environment of PCa, refining personalized treatment strategies, and increasing the ability to predict the outcome. This systematic ...

Physica Medica, 2021

Machine learning (ML) applications in medicine represent an emerging field of research with the p... more Machine learning (ML) applications in medicine represent an emerging field of research with the potential to revolutionize the field of radiation oncology, in particular. With the era of big data, the utilization of machine learning algorithms in radiation oncology research is growing fast with applications including patient diagnosis and staging of cancer, treatment simulation, treatment planning, treatment delivery, quality assurance, and treatment response and outcome predictions. In this chapter, we provide the interested reader with an overview of the ongoing advances and cutting-edge applications of state-of-the-art ML techniques in radiation oncology process from the radiotherapy workflow perspective, starting from patient's diagnosis to follow-up. We present with discussion the areas where ML has presently been used and also areas where ML could be applied to improve the efficiency (i.e., optimizing and automating the clinical processes) and quality (i.e., potentials for decision-making support toward a practical application of precision medicine in radiation therapy) of patient care.

Medical physics, 2018

To investigate the clinical implication of performing pre-treatment dosimetry for Y-microspheres ... more To investigate the clinical implication of performing pre-treatment dosimetry for Y-microspheres liver radioembolization on Tc-MAA SPECT images reconstructed without attenuation or scatter correction and quantified with the patient relative calibration methodology. Twenty-five patients treated with SIR-Spheres at Istituto Europeo di Oncologia and 31 patients treated with TheraSphere at Istituto Nazionale Tumori were considered. For each acquired Tc-MAA SPECT, four reconstructions were performed: with attenuation and scatter correction (AC_SC), only attenuation (AC_NoSC), only scatter (NoAC_SC) and without corrections (NoAC_NoSC). Absorbed dose maps were calculated from the activity maps, quantified applying the patient relative calibration to the SPECT images. Whole Liver (WL) and Tumor (T) regions were drawn on CT images. Injected Liver (IL) region was defined including the voxels receiving absorbed dose >3.8 Gy/GBq. Whole Healthy Liver (WHL) and Healthy Injected Liver (HIL) reg...

European Radiology Experimental

In prostate cancer (PCa), the use of new radiopharmaceuticals has improved the accuracy of diagno... more In prostate cancer (PCa), the use of new radiopharmaceuticals has improved the accuracy of diagnosis and staging, refined surveillance strategies, and introduced specific and personalized radioreceptor therapies. Nuclear medicine, therefore, holds great promise for improving the quality of life of PCa patients, through managing and processing a vast amount of molecular imaging data and beyond, using a multi-omics approach and improving patients’ risk-stratification for tailored medicine. Artificial intelligence (AI) and radiomics may allow clinicians to improve the overall efficiency and accuracy of using these “big data” in both the diagnostic and theragnostic field: from technical aspects (such as semi-automatization of tumor segmentation, image reconstruction, and interpretation) to clinical outcomes, improving a deeper understanding of the molecular environment of PCa, refining personalized treatment strategies, and increasing the ability to predict the outcome. This systematic ...

Physica Medica, 2021

Machine learning (ML) applications in medicine represent an emerging field of research with the p... more Machine learning (ML) applications in medicine represent an emerging field of research with the potential to revolutionize the field of radiation oncology, in particular. With the era of big data, the utilization of machine learning algorithms in radiation oncology research is growing fast with applications including patient diagnosis and staging of cancer, treatment simulation, treatment planning, treatment delivery, quality assurance, and treatment response and outcome predictions. In this chapter, we provide the interested reader with an overview of the ongoing advances and cutting-edge applications of state-of-the-art ML techniques in radiation oncology process from the radiotherapy workflow perspective, starting from patient's diagnosis to follow-up. We present with discussion the areas where ML has presently been used and also areas where ML could be applied to improve the efficiency (i.e., optimizing and automating the clinical processes) and quality (i.e., potentials for decision-making support toward a practical application of precision medicine in radiation therapy) of patient care.

Medical physics, 2018

To investigate the clinical implication of performing pre-treatment dosimetry for Y-microspheres ... more To investigate the clinical implication of performing pre-treatment dosimetry for Y-microspheres liver radioembolization on Tc-MAA SPECT images reconstructed without attenuation or scatter correction and quantified with the patient relative calibration methodology. Twenty-five patients treated with SIR-Spheres at Istituto Europeo di Oncologia and 31 patients treated with TheraSphere at Istituto Nazionale Tumori were considered. For each acquired Tc-MAA SPECT, four reconstructions were performed: with attenuation and scatter correction (AC_SC), only attenuation (AC_NoSC), only scatter (NoAC_SC) and without corrections (NoAC_NoSC). Absorbed dose maps were calculated from the activity maps, quantified applying the patient relative calibration to the SPECT images. Whole Liver (WL) and Tumor (T) regions were drawn on CT images. Injected Liver (IL) region was defined including the voxels receiving absorbed dose >3.8 Gy/GBq. Whole Healthy Liver (WHL) and Healthy Injected Liver (HIL) reg...

Medical Physics, 2016

Purpose: Many centers aim to plan liver transarterial radioembolization (TARE) with dosimetry, ev... more Purpose: Many centers aim to plan liver transarterial radioembolization (TARE) with dosimetry, even without CT-based attenuation correction (AC), or with unoptimized scatter correction (SC) methods. This work investigates the impact of presence vs absence of such corrections, and limited spatial resolution, on 3D dosimetry for TARE. Methods: Three voxelized phantoms were derived from CT images of real patients with different body sizes. Simulations of 99m Tc-SPECT projections were performed with the SIMIND code, assuming three activity distributions in the liver: uniform, inside a "liver's segment," or distributing multiple uptaking nodules ("nonuniform liver"), with a tumoral liver/healthy parenchyma ratio of 5:1. Projection data were reconstructed by a commercial workstation, with OSEM protocol not specifically optimized for dosimetry (spatial resolution of 12.6 mm), with/without SC (optimized, or with parameters predefined by the manufacturer; dual energy window), and with/without AC. Activity in voxels was calculated by a relative calibration, assuming identical microspheres and 99m Tc-SPECT counts spatial distribution. 3D dose distributions were calculated by convolution with 90 Y voxel S-values, assuming permanent trapping of microspheres. Cumulative dose-volume histograms in

Physica Medica, 2016

Introduction: PET/CT imaging allows to obtain brain metabolic and functional information that is ... more 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 cm 3 , 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.

Physica Medica, 2016

Results: The mean absorbed dose and standard deviation for 4 lesions (mean [σ%]) were: 434 mGy [1... more Results: The mean absorbed dose and standard deviation for 4 lesions (mean [σ%]) were: 434 mGy [15%] and 516 mGy [21%] for right and left humeral heads, 1205 mGy [14%] and 781 mGy [8%] for right and left glenoids. The total absorbed dose after the whole treatment, considering the relativebiological-effectiveness of alpha particles (RBE = 5), yielded a DRBE range of 13-36 Gy. TNT showed an overall reduction in two cases (−42% and −48%), but for most lesions it remained fairly constant. Conclusion: The inter-fraction variability of dosimetric assessments indicates that dosimetry would be advisable more than once, for a more accurate estimation of the total absorbed dose. TNT constancy highlights that 223Radichloride therapy tends to prevent further progression of the osseous disease, leading to chronicity of the metastatic status.

Physica Medica, 2016

Introduction: PET/CT imaging allows to obtain brain metabolic and functional information that is ... more 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 cm 3 , 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.

Annals of nuclear medicine, Jan 27, 2015

A 70-year-old man affected by bone metastases from castration resistant prostate cancer underwent... more A 70-year-old man affected by bone metastases from castration resistant prostate cancer underwent Alpharadin ((223)Ra-dichloride) therapy (6 administrations of 50 kBq per kg i.v., once every 4 weeks). The inter-fraction variability of the absorbed dose to lesions was evaluated for four injections. Dosimetric assessments were performed following the MIRD approach and a recently published methodology. The mean absorbed dose and standard deviation for 4 lesions [mean (σ %)] were: 434 mGy (15 %) and 516 mGy (21 %) for the right and left humeral head, 1205 mGy (14 %) and 781 mGy (8 %) for the right and left glenoid. The estimated total absorbed dose after the whole treatment, considering also the relative-biological effectiveness of alpha particles (RBE = 5), yielded a D RBE range of 13-36 Gy. A good correlation between (99m)Tc and (223)Ra uptake was obtained (R (2) = 0.7613). The tumour-non-tumour (TNT) ratio of 8 lesions (those above, plus 4 additional), monitored by six (99m)Tc-MDP bo...

European Journal of Nuclear Medicine and Molecular Imaging, 2015

Purpose Ra-dichloride is an alpha-emitting radiopharmaceutical used in the treatment of bone meta... more Purpose Ra-dichloride is an alpha-emitting radiopharmaceutical used in the treatment of bone metastases from castrationresistant prostate cancer. Image-based dosimetric studies remain challenging because the emitted photons are few. The aim of this study was to implement a methodology for in-vivo quantitative planar imaging, and to assess the absorbed dose to lesions using the MIRD approach. Methods The study included nine Caucasian patients with 24 lesions (6 humeral head lesions, 4 iliac wing lesions, 2 scapular lesions, 5 trochanter lesions, 3 vertebral lesions, 3 glenoid lesions, 1 coxofemoral lesion). The treatment consisted of six injections (one every 4 weeks) of 50 kBq per kg body weight. Gamma-camera calibrations for 223 Ra included measurements of sensitivity and transmission curves. Patients were statically imaged for 30 min, using an MEGP collimator, double-peak acquisition, and filtering to improve the image quality. Lesions were delineated on 99m Tc-MDP whole-body images, and the ROIs superimposed on the 223 Ra images after image coregistration. The activity was quantified with background, attenuation, and scatter correction. Absorbed doses were assessed deriving the S values from the S factors for softtissue spheres of OLINDA/EXM, evaluating the lesion volumes by delineation on the CT images. Results In 12 lesions with a wash-in phase the biokinetics were assumed to be biexponential, and to be monoexponential in the remainder. The optimal timing for serial acquisitions was between 1 and 5 h, between 18 and 24 h, between 48 and 60 h, and between 7 and 15 days. The error in cumulated activity neglecting the wash-in phase was between 2 % and 12 %. The mean effective half-life (T 1/2eff) of 223 Ra was 8.2 days (range 5.5-11.4 days). The absorbed dose (D) after the first injection was 0.7 Gy (range 0.2-1.9 Gy. Considering the relative biological effectiveness (RBE) of alpha particles (RBE=5), D RBE =899 mGy/MBq (range 340-2,450 mGy/ MBq). The percent uptake of 99m Tc and 223 Ra (activity extrapolated to t=0) were significantly correlated. Conclusion The feasibility of in vivo quantitative imaging in 223 Ra therapy was confirmed. The lesion uptake of 223 Radichloride was significantly correlated with that of 99m Tc-MDP. The D RBE to lesions per unit administered activity was much higher than that of other bone-seeking radiopharmaceuticals, but considering a standard administration of 21 MBq (six injections of 50 kBq/kg to a 70-kg patient), the mean cumulative value of D RBE was about 19 Gy, and was therefore in the range of those of other radiopharmaceuticals. The macrodosimetry of bone metastases in treatments with 223 Ra-dichloride is feasible, but more work is needed to demonstrate its helpfulness in predicting clinical outcomes.

European Radiology Experimental

In prostate cancer (PCa), the use of new radiopharmaceuticals has improved the accuracy of diagno... more In prostate cancer (PCa), the use of new radiopharmaceuticals has improved the accuracy of diagnosis and staging, refined surveillance strategies, and introduced specific and personalized radioreceptor therapies. Nuclear medicine, therefore, holds great promise for improving the quality of life of PCa patients, through managing and processing a vast amount of molecular imaging data and beyond, using a multi-omics approach and improving patients’ risk-stratification for tailored medicine. Artificial intelligence (AI) and radiomics may allow clinicians to improve the overall efficiency and accuracy of using these “big data” in both the diagnostic and theragnostic field: from technical aspects (such as semi-automatization of tumor segmentation, image reconstruction, and interpretation) to clinical outcomes, improving a deeper understanding of the molecular environment of PCa, refining personalized treatment strategies, and increasing the ability to predict the outcome. This systematic ...

Physica Medica, 2021

Machine learning (ML) applications in medicine represent an emerging field of research with the p... more Machine learning (ML) applications in medicine represent an emerging field of research with the potential to revolutionize the field of radiation oncology, in particular. With the era of big data, the utilization of machine learning algorithms in radiation oncology research is growing fast with applications including patient diagnosis and staging of cancer, treatment simulation, treatment planning, treatment delivery, quality assurance, and treatment response and outcome predictions. In this chapter, we provide the interested reader with an overview of the ongoing advances and cutting-edge applications of state-of-the-art ML techniques in radiation oncology process from the radiotherapy workflow perspective, starting from patient's diagnosis to follow-up. We present with discussion the areas where ML has presently been used and also areas where ML could be applied to improve the efficiency (i.e., optimizing and automating the clinical processes) and quality (i.e., potentials for decision-making support toward a practical application of precision medicine in radiation therapy) of patient care.

Medical physics, 2018

To investigate the clinical implication of performing pre-treatment dosimetry for Y-microspheres ... more To investigate the clinical implication of performing pre-treatment dosimetry for Y-microspheres liver radioembolization on Tc-MAA SPECT images reconstructed without attenuation or scatter correction and quantified with the patient relative calibration methodology. Twenty-five patients treated with SIR-Spheres at Istituto Europeo di Oncologia and 31 patients treated with TheraSphere at Istituto Nazionale Tumori were considered. For each acquired Tc-MAA SPECT, four reconstructions were performed: with attenuation and scatter correction (AC_SC), only attenuation (AC_NoSC), only scatter (NoAC_SC) and without corrections (NoAC_NoSC). Absorbed dose maps were calculated from the activity maps, quantified applying the patient relative calibration to the SPECT images. Whole Liver (WL) and Tumor (T) regions were drawn on CT images. Injected Liver (IL) region was defined including the voxels receiving absorbed dose >3.8 Gy/GBq. Whole Healthy Liver (WHL) and Healthy Injected Liver (HIL) reg...

European Radiology Experimental

In prostate cancer (PCa), the use of new radiopharmaceuticals has improved the accuracy of diagno... more In prostate cancer (PCa), the use of new radiopharmaceuticals has improved the accuracy of diagnosis and staging, refined surveillance strategies, and introduced specific and personalized radioreceptor therapies. Nuclear medicine, therefore, holds great promise for improving the quality of life of PCa patients, through managing and processing a vast amount of molecular imaging data and beyond, using a multi-omics approach and improving patients’ risk-stratification for tailored medicine. Artificial intelligence (AI) and radiomics may allow clinicians to improve the overall efficiency and accuracy of using these “big data” in both the diagnostic and theragnostic field: from technical aspects (such as semi-automatization of tumor segmentation, image reconstruction, and interpretation) to clinical outcomes, improving a deeper understanding of the molecular environment of PCa, refining personalized treatment strategies, and increasing the ability to predict the outcome. This systematic ...

Physica Medica, 2021

Machine learning (ML) applications in medicine represent an emerging field of research with the p... more Machine learning (ML) applications in medicine represent an emerging field of research with the potential to revolutionize the field of radiation oncology, in particular. With the era of big data, the utilization of machine learning algorithms in radiation oncology research is growing fast with applications including patient diagnosis and staging of cancer, treatment simulation, treatment planning, treatment delivery, quality assurance, and treatment response and outcome predictions. In this chapter, we provide the interested reader with an overview of the ongoing advances and cutting-edge applications of state-of-the-art ML techniques in radiation oncology process from the radiotherapy workflow perspective, starting from patient's diagnosis to follow-up. We present with discussion the areas where ML has presently been used and also areas where ML could be applied to improve the efficiency (i.e., optimizing and automating the clinical processes) and quality (i.e., potentials for decision-making support toward a practical application of precision medicine in radiation therapy) of patient care.

Medical physics, 2018

To investigate the clinical implication of performing pre-treatment dosimetry for Y-microspheres ... more To investigate the clinical implication of performing pre-treatment dosimetry for Y-microspheres liver radioembolization on Tc-MAA SPECT images reconstructed without attenuation or scatter correction and quantified with the patient relative calibration methodology. Twenty-five patients treated with SIR-Spheres at Istituto Europeo di Oncologia and 31 patients treated with TheraSphere at Istituto Nazionale Tumori were considered. For each acquired Tc-MAA SPECT, four reconstructions were performed: with attenuation and scatter correction (AC_SC), only attenuation (AC_NoSC), only scatter (NoAC_SC) and without corrections (NoAC_NoSC). Absorbed dose maps were calculated from the activity maps, quantified applying the patient relative calibration to the SPECT images. Whole Liver (WL) and Tumor (T) regions were drawn on CT images. Injected Liver (IL) region was defined including the voxels receiving absorbed dose >3.8 Gy/GBq. Whole Healthy Liver (WHL) and Healthy Injected Liver (HIL) reg...

Medical Physics, 2016

Purpose: Many centers aim to plan liver transarterial radioembolization (TARE) with dosimetry, ev... more Purpose: Many centers aim to plan liver transarterial radioembolization (TARE) with dosimetry, even without CT-based attenuation correction (AC), or with unoptimized scatter correction (SC) methods. This work investigates the impact of presence vs absence of such corrections, and limited spatial resolution, on 3D dosimetry for TARE. Methods: Three voxelized phantoms were derived from CT images of real patients with different body sizes. Simulations of 99m Tc-SPECT projections were performed with the SIMIND code, assuming three activity distributions in the liver: uniform, inside a "liver's segment," or distributing multiple uptaking nodules ("nonuniform liver"), with a tumoral liver/healthy parenchyma ratio of 5:1. Projection data were reconstructed by a commercial workstation, with OSEM protocol not specifically optimized for dosimetry (spatial resolution of 12.6 mm), with/without SC (optimized, or with parameters predefined by the manufacturer; dual energy window), and with/without AC. Activity in voxels was calculated by a relative calibration, assuming identical microspheres and 99m Tc-SPECT counts spatial distribution. 3D dose distributions were calculated by convolution with 90 Y voxel S-values, assuming permanent trapping of microspheres. Cumulative dose-volume histograms in

Physica Medica, 2016

Introduction: PET/CT imaging allows to obtain brain metabolic and functional information that is ... more 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 cm 3 , 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.

Physica Medica, 2016

Results: The mean absorbed dose and standard deviation for 4 lesions (mean [σ%]) were: 434 mGy [1... more Results: The mean absorbed dose and standard deviation for 4 lesions (mean [σ%]) were: 434 mGy [15%] and 516 mGy [21%] for right and left humeral heads, 1205 mGy [14%] and 781 mGy [8%] for right and left glenoids. The total absorbed dose after the whole treatment, considering the relativebiological-effectiveness of alpha particles (RBE = 5), yielded a DRBE range of 13-36 Gy. TNT showed an overall reduction in two cases (−42% and −48%), but for most lesions it remained fairly constant. Conclusion: The inter-fraction variability of dosimetric assessments indicates that dosimetry would be advisable more than once, for a more accurate estimation of the total absorbed dose. TNT constancy highlights that 223Radichloride therapy tends to prevent further progression of the osseous disease, leading to chronicity of the metastatic status.

Physica Medica, 2016

Introduction: PET/CT imaging allows to obtain brain metabolic and functional information that is ... more 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 cm 3 , 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.

Annals of nuclear medicine, Jan 27, 2015

A 70-year-old man affected by bone metastases from castration resistant prostate cancer underwent... more A 70-year-old man affected by bone metastases from castration resistant prostate cancer underwent Alpharadin ((223)Ra-dichloride) therapy (6 administrations of 50 kBq per kg i.v., once every 4 weeks). The inter-fraction variability of the absorbed dose to lesions was evaluated for four injections. Dosimetric assessments were performed following the MIRD approach and a recently published methodology. The mean absorbed dose and standard deviation for 4 lesions [mean (σ %)] were: 434 mGy (15 %) and 516 mGy (21 %) for the right and left humeral head, 1205 mGy (14 %) and 781 mGy (8 %) for the right and left glenoid. The estimated total absorbed dose after the whole treatment, considering also the relative-biological effectiveness of alpha particles (RBE = 5), yielded a D RBE range of 13-36 Gy. A good correlation between (99m)Tc and (223)Ra uptake was obtained (R (2) = 0.7613). The tumour-non-tumour (TNT) ratio of 8 lesions (those above, plus 4 additional), monitored by six (99m)Tc-MDP bo...

European Journal of Nuclear Medicine and Molecular Imaging, 2015

Purpose Ra-dichloride is an alpha-emitting radiopharmaceutical used in the treatment of bone meta... more Purpose Ra-dichloride is an alpha-emitting radiopharmaceutical used in the treatment of bone metastases from castrationresistant prostate cancer. Image-based dosimetric studies remain challenging because the emitted photons are few. The aim of this study was to implement a methodology for in-vivo quantitative planar imaging, and to assess the absorbed dose to lesions using the MIRD approach. Methods The study included nine Caucasian patients with 24 lesions (6 humeral head lesions, 4 iliac wing lesions, 2 scapular lesions, 5 trochanter lesions, 3 vertebral lesions, 3 glenoid lesions, 1 coxofemoral lesion). The treatment consisted of six injections (one every 4 weeks) of 50 kBq per kg body weight. Gamma-camera calibrations for 223 Ra included measurements of sensitivity and transmission curves. Patients were statically imaged for 30 min, using an MEGP collimator, double-peak acquisition, and filtering to improve the image quality. Lesions were delineated on 99m Tc-MDP whole-body images, and the ROIs superimposed on the 223 Ra images after image coregistration. The activity was quantified with background, attenuation, and scatter correction. Absorbed doses were assessed deriving the S values from the S factors for softtissue spheres of OLINDA/EXM, evaluating the lesion volumes by delineation on the CT images. Results In 12 lesions with a wash-in phase the biokinetics were assumed to be biexponential, and to be monoexponential in the remainder. The optimal timing for serial acquisitions was between 1 and 5 h, between 18 and 24 h, between 48 and 60 h, and between 7 and 15 days. The error in cumulated activity neglecting the wash-in phase was between 2 % and 12 %. The mean effective half-life (T 1/2eff) of 223 Ra was 8.2 days (range 5.5-11.4 days). The absorbed dose (D) after the first injection was 0.7 Gy (range 0.2-1.9 Gy. Considering the relative biological effectiveness (RBE) of alpha particles (RBE=5), D RBE =899 mGy/MBq (range 340-2,450 mGy/ MBq). The percent uptake of 99m Tc and 223 Ra (activity extrapolated to t=0) were significantly correlated. Conclusion The feasibility of in vivo quantitative imaging in 223 Ra therapy was confirmed. The lesion uptake of 223 Radichloride was significantly correlated with that of 99m Tc-MDP. The D RBE to lesions per unit administered activity was much higher than that of other bone-seeking radiopharmaceuticals, but considering a standard administration of 21 MBq (six injections of 50 kBq/kg to a 70-kg patient), the mean cumulative value of D RBE was about 19 Gy, and was therefore in the range of those of other radiopharmaceuticals. The macrodosimetry of bone metastases in treatments with 223 Ra-dichloride is feasible, but more work is needed to demonstrate its helpfulness in predicting clinical outcomes.