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CT in metastatic brain tumors
Abstracts / Physica Medica 30 (2014) e75ee121
Purpose: To present an EGSnrc-based model of the Gamma Knife Perfexion (PFX) radiosurgery unit used for Monte Carlo (MC) dosimetry calculations. Emphasis is given on the effect of specific model and scoring parameters on PFX output factor (OF) and relative dose profile results. Materials and methods: A detailed model of the PFX system was established using the C++ geometry package of the EGSnrc MC code, based on relevant drawings provided by the vendor. All 192 Co-60 sources along with their capsules and bushing were modeled in a single input file per collimator size (16mm, 8mm and 4mm). Dosimetry calculations were performed in a spherical, 16cm diameter water phantom using the “egs_chamber” user code. The angular distribution of the photons emitted from each source was assumed to be isotropic. The developed PFX model was benchmarked against off axis relative dose profiles measured with radiochromic films. Dose was scored in concentric spherical volumes, centered at UCP, with radii ranging from 0.2mm to 3mm and used to evaluate volume averaging effects on OF results. Simulations were repeated for confined angular distributions of the emitted photons to assess the gained simulation efficiency against dosimetric accuracy. In specific, the cone half angle, as defined with respect to the source channel central axis, varied from 5o to 90o. Results and conclusion: Confinement of the emitted photons angular distribution resulted in a time efficiency gain factor of up to 210 (for 5o cone half angle and the 4mm collimator), and had no considerable effect on relative dose profile data. Contrarily, the gained simulation efficiency was found to come at the expense of the accuracy of the calculated OF values, leading to an overestimation of up to 6% and 3.5% for the 4mm and 8mm collimators, respectively, as compared to isotropic photon emission. Volume averaging was found to impact OF results for sensitive volume radii greater than 0.5mm and 1.25mm for the 4mm and 8mm collimators, respectively. The developed PFX model will be used to determine the kQcln correction factors corresponding to commonly used detectors for PFX OF measurements.
CONTRIBUTION OF FLT-PET/CT IN METASTATIC BRAIN TUMORS Alexandra Nikaki a, Roxani Efthymiadou a, Ioannis Tsougos b, Vassilios Prassopoulos a, Vassiliki Filippi a, Fani Vlachou a, Despina Savvidou a, Theodoros Pipikos a, Ioannis Andreou a, Panagiotis Georgoulias c. a PET/CT Department, HYGEIA SA, Greece; b Medical Physics Department, University of Thessaly, Greece; c Nuclear Medicine Department, University of Thessaly, Greece Aim: To explore the role of FLT-PET/CT in recurrent metastatic brain lesions. Method-material: 13 patients underwent 17 FLT-PET examinations for evaluation of metastatic brain lesions. The primary tumor site was: breast cancer in 7 cases, lung cancer in 7, thymoma in 2, and melanoma in 1 case. All patients had received the appropriate treatment during the course of disease and all of them had received radiotherapy for metastatic brain disease, while in 2/17 cases additional surgical excision of the brain lesion was performed. FLT-PET/CT was performed 55±5min after the iv administration of 18F-FLT at a Siemens Biograph LSO PET/CT device. Findings were evaluated visually as positive or negative: any finding with FLT uptake clearly above the background activity was characterized as positive. Semiquantitative assessment was also used, with the calculation of SUVmax and tumor-to-background ratio (T/B: SUVmax of the tumor/ SUVmean of the background). Results: FLT-PET/CT was characterized negative in 3 cases and positive in 14 (15 lesions). Average SUVmax and T/B were 2.27±1.3 and 11.62±5.47 respectively. Using paired t-test, T/B values were statistically significant higher than the SUVmax values (p <0.05). In 12 cases patients were referred for treatment after FLT-PET examination, 11 of whom had a positive PET examination, while data is missing for 1. In 2 FLT-PET positive cases the patients were referred for biopsy, both of which were negative: 1 of these patients exhibited progressive disease in the next follow-up examination. In the other PET-positive/biopsy-negative case, FLT uptake pattern was diffuse and SUVmax was 1.29. In 2 FLT-PET-negative cases patients were put under surveillance. In 1 FLT-PET negative case, the patient was referred for chemotherapy, due to disease lesions other than brain.
e109
Conclusion: Admitting the referral bias and the small and inhomogeneous sample, our results indicate that 18F-FLT- РЕΤ, by offering additional functional information, may be a useful tool in evaluation of metastatic brain lesions. Average SUVmax and T/B values differ substantially, possibly due to the more constant background activity. Variability noted mostly in T/B values could be attributed to differences in primary site and treatment response.
THE USE OF CENTROMERIC/TELOMERIC PNA PROBES IN PREMATURELY CONDENSED CHROMOSOMES OF PERIPHERAL BLOOD LYMPHOCYTES FOR ABSORBED DOSE ESTIMATION I. Karachristou a, D. Zafiropoulos b, M. Karakosta a, V. Hatzi a, G. Pantelias a, G. Terzoudi a. a Health Physics, Radiobiology & Cytogenetics laboratory, Institute of Nuclear & Radiological Sciences & Technology, Energy & Safety, NCSR “Demokritos”, Athens, Greece; b Laboratori Nazionali di Legnaro, Istituto Nazionale di Fisica Nucleare, Legnaro, Italy Background: The frequency of dicentric chromosomes in human peripheral blood lymphocytes at metaphase is considered as the “goldstandard” for biological dosimetry and at present is the most widely used method for dose assessment. This methodology requires lymphocyte culture and analysis time of more than three days. Such long time period, is inadequate in radiation emergency medicine since a rapid and accurate estimation of the dose is considered to be a high priority. Alternatively, cell fusion mediated premature chromosome condensation (PCC) enables the observation of radiation-induced cytogenetic damage directly in non-stimulated lymphocytes without the need of blood culturing. Quantification of an exposure by means of this method has been limited so far mainly to the analysis of chromosome fragments and rings. This limitation is due to the fact that staining with Giemsa of prematurely condensed chromosomes (PCCs) does not allow visualization of the centromeric regions and, consequently, the identification of dicentrics, centric rings, and acentric fragments. In the present work, we overcome this shortcoming by developing a methodology enabling us the detection of dicentric chromosomes rapidly and accurately in non-stimulated lymphocyte PCCs. Materials and methods: The methodology of cell fusion mediated premature chromosome condensation was used and combined with fluorescence in situ hybridization (FISH) technique, using simultaneously telomere and centromere peptide nucleid acid (PNA) probes. For detecting of dicentric chromosomes in cultured lymphocytes conventional metaphase analysis was used. Results: Analysis of dicentrics, centric rings and acentric fragments in nonstimulated lymphocyte PCCs was carried out and dose-response curves for doses up to 8 Gy have been constructed. For comparison, dose response curves were also obtained using the conventional metaphase analysis in stimulated lymphocytes. Discussion: FISH analysis with centromeric/telomeric PNA probes in G0lymphocyte PCCs is proved to be an effective, sensitive and fast approach for the estimation of absorbed doses especially in case of radiation emergency medicine. The advantages of this new approach in comparison with the conventional method will be discussed. STUDY OF THE REPLACEMENT-UPDATE OF THE PACS/RIS SYSTEM IN THE MEDICAL IMAGING DEPARTMENT OF THE IASO GENERAL HOSPITAL Ioanna Tzovara Foteini Stromatia MScMedical Physicist a, MDRadiologist b. a Department of Medical physics IASO General Hospital, Greece; b Department of Medical Imaging IASO General Hospital, Mesogion 264, 15562 Holargos, Greece Aim: The aim of the study was to update or replace the PACS/RIS system of the medical imaging departments, of IASO General Hospital, after eight years of archiving 5341 G-Bytes of medical data, since the installation in 2002, in order to achieve better work flow and faster medical diagnosis. Materials and methods: The archiving and management of medical imaging data, in our Hospital, were performed using a PACS/RIS system,
Purpose: To present an EGSnrc-based model of the Gamma Knife Perfexion (PFX) radiosurgery unit used for Monte Carlo (MC) dosimetry calculations. Emphasis is given on the effect of specific model and scoring parameters on PFX output factor (OF) and relative dose profile results. Materials and methods: A detailed model of the PFX system was established using the C++ geometry package of the EGSnrc MC code, based on relevant drawings provided by the vendor. All 192 Co-60 sources along with their capsules and bushing were modeled in a single input file per collimator size (16mm, 8mm and 4mm). Dosimetry calculations were performed in a spherical, 16cm diameter water phantom using the “egs_chamber” user code. The angular distribution of the photons emitted from each source was assumed to be isotropic. The developed PFX model was benchmarked against off axis relative dose profiles measured with radiochromic films. Dose was scored in concentric spherical volumes, centered at UCP, with radii ranging from 0.2mm to 3mm and used to evaluate volume averaging effects on OF results. Simulations were repeated for confined angular distributions of the emitted photons to assess the gained simulation efficiency against dosimetric accuracy. In specific, the cone half angle, as defined with respect to the source channel central axis, varied from 5o to 90o. Results and conclusion: Confinement of the emitted photons angular distribution resulted in a time efficiency gain factor of up to 210 (for 5o cone half angle and the 4mm collimator), and had no considerable effect on relative dose profile data. Contrarily, the gained simulation efficiency was found to come at the expense of the accuracy of the calculated OF values, leading to an overestimation of up to 6% and 3.5% for the 4mm and 8mm collimators, respectively, as compared to isotropic photon emission. Volume averaging was found to impact OF results for sensitive volume radii greater than 0.5mm and 1.25mm for the 4mm and 8mm collimators, respectively. The developed PFX model will be used to determine the kQcln correction factors corresponding to commonly used detectors for PFX OF measurements.
CONTRIBUTION OF FLT-PET/CT IN METASTATIC BRAIN TUMORS Alexandra Nikaki a, Roxani Efthymiadou a, Ioannis Tsougos b, Vassilios Prassopoulos a, Vassiliki Filippi a, Fani Vlachou a, Despina Savvidou a, Theodoros Pipikos a, Ioannis Andreou a, Panagiotis Georgoulias c. a PET/CT Department, HYGEIA SA, Greece; b Medical Physics Department, University of Thessaly, Greece; c Nuclear Medicine Department, University of Thessaly, Greece Aim: To explore the role of FLT-PET/CT in recurrent metastatic brain lesions. Method-material: 13 patients underwent 17 FLT-PET examinations for evaluation of metastatic brain lesions. The primary tumor site was: breast cancer in 7 cases, lung cancer in 7, thymoma in 2, and melanoma in 1 case. All patients had received the appropriate treatment during the course of disease and all of them had received radiotherapy for metastatic brain disease, while in 2/17 cases additional surgical excision of the brain lesion was performed. FLT-PET/CT was performed 55±5min after the iv administration of 18F-FLT at a Siemens Biograph LSO PET/CT device. Findings were evaluated visually as positive or negative: any finding with FLT uptake clearly above the background activity was characterized as positive. Semiquantitative assessment was also used, with the calculation of SUVmax and tumor-to-background ratio (T/B: SUVmax of the tumor/ SUVmean of the background). Results: FLT-PET/CT was characterized negative in 3 cases and positive in 14 (15 lesions). Average SUVmax and T/B were 2.27±1.3 and 11.62±5.47 respectively. Using paired t-test, T/B values were statistically significant higher than the SUVmax values (p <0.05). In 12 cases patients were referred for treatment after FLT-PET examination, 11 of whom had a positive PET examination, while data is missing for 1. In 2 FLT-PET positive cases the patients were referred for biopsy, both of which were negative: 1 of these patients exhibited progressive disease in the next follow-up examination. In the other PET-positive/biopsy-negative case, FLT uptake pattern was diffuse and SUVmax was 1.29. In 2 FLT-PET-negative cases patients were put under surveillance. In 1 FLT-PET negative case, the patient was referred for chemotherapy, due to disease lesions other than brain.
e109
Conclusion: Admitting the referral bias and the small and inhomogeneous sample, our results indicate that 18F-FLT- РЕΤ, by offering additional functional information, may be a useful tool in evaluation of metastatic brain lesions. Average SUVmax and T/B values differ substantially, possibly due to the more constant background activity. Variability noted mostly in T/B values could be attributed to differences in primary site and treatment response.
THE USE OF CENTROMERIC/TELOMERIC PNA PROBES IN PREMATURELY CONDENSED CHROMOSOMES OF PERIPHERAL BLOOD LYMPHOCYTES FOR ABSORBED DOSE ESTIMATION I. Karachristou a, D. Zafiropoulos b, M. Karakosta a, V. Hatzi a, G. Pantelias a, G. Terzoudi a. a Health Physics, Radiobiology & Cytogenetics laboratory, Institute of Nuclear & Radiological Sciences & Technology, Energy & Safety, NCSR “Demokritos”, Athens, Greece; b Laboratori Nazionali di Legnaro, Istituto Nazionale di Fisica Nucleare, Legnaro, Italy Background: The frequency of dicentric chromosomes in human peripheral blood lymphocytes at metaphase is considered as the “goldstandard” for biological dosimetry and at present is the most widely used method for dose assessment. This methodology requires lymphocyte culture and analysis time of more than three days. Such long time period, is inadequate in radiation emergency medicine since a rapid and accurate estimation of the dose is considered to be a high priority. Alternatively, cell fusion mediated premature chromosome condensation (PCC) enables the observation of radiation-induced cytogenetic damage directly in non-stimulated lymphocytes without the need of blood culturing. Quantification of an exposure by means of this method has been limited so far mainly to the analysis of chromosome fragments and rings. This limitation is due to the fact that staining with Giemsa of prematurely condensed chromosomes (PCCs) does not allow visualization of the centromeric regions and, consequently, the identification of dicentrics, centric rings, and acentric fragments. In the present work, we overcome this shortcoming by developing a methodology enabling us the detection of dicentric chromosomes rapidly and accurately in non-stimulated lymphocyte PCCs. Materials and methods: The methodology of cell fusion mediated premature chromosome condensation was used and combined with fluorescence in situ hybridization (FISH) technique, using simultaneously telomere and centromere peptide nucleid acid (PNA) probes. For detecting of dicentric chromosomes in cultured lymphocytes conventional metaphase analysis was used. Results: Analysis of dicentrics, centric rings and acentric fragments in nonstimulated lymphocyte PCCs was carried out and dose-response curves for doses up to 8 Gy have been constructed. For comparison, dose response curves were also obtained using the conventional metaphase analysis in stimulated lymphocytes. Discussion: FISH analysis with centromeric/telomeric PNA probes in G0lymphocyte PCCs is proved to be an effective, sensitive and fast approach for the estimation of absorbed doses especially in case of radiation emergency medicine. The advantages of this new approach in comparison with the conventional method will be discussed. STUDY OF THE REPLACEMENT-UPDATE OF THE PACS/RIS SYSTEM IN THE MEDICAL IMAGING DEPARTMENT OF THE IASO GENERAL HOSPITAL Ioanna Tzovara Foteini Stromatia MScMedical Physicist a, MDRadiologist b. a Department of Medical physics IASO General Hospital, Greece; b Department of Medical Imaging IASO General Hospital, Mesogion 264, 15562 Holargos, Greece Aim: The aim of the study was to update or replace the PACS/RIS system of the medical imaging departments, of IASO General Hospital, after eight years of archiving 5341 G-Bytes of medical data, since the installation in 2002, in order to achieve better work flow and faster medical diagnosis. Materials and methods: The archiving and management of medical imaging data, in our Hospital, were performed using a PACS/RIS system,