- Email: [email protected]
Experimental study of the peripheral dose outside the applicator for electron beams used in the external radiotherapy
Abstracts of the SFPM Annual Meeting 2013 / Physica Medica 29 (2013) e1–e46
was focused on the Monte Carlo modeling of such an EPID in order to simulate both planar and 3D CBCT images. Methods: The work presented here follows a preliminary study in which the treatment part of a clinical LINAC (Siemens Oncor) was modeled in GATE v6.2. The objective was to calculate the dose delivered by complex treatments like IMRT. The objective of the study is to extend this model by incorporating the imaging part of the LINAC, which consists of a flat panel detector (Perkin Elmer XRD1640). For this purpose, geometrical and physical data provided by the manufacturer were first accurately modeled in GATE. Assessments of portal imaging were performed by performing dose calculations in a CQ IMRT phantom with GATE for two measurement points with protocols of 8, 15 and 60 UM and comparing the doses with clinical measurements. And with performing 2D CT projections over a 200° arc, 1° increments, and 41 cm 41 cm field of view for homogeneous and heterogeneous structures (introduction of a patient head and neck CT patient). Results: For the calculation of the deposit dose at the isocentre of the CQ IMRT phantom, respectively GATE gave doses of 5.734 0.169, 11.008 0.777 and 46.006 0.711 cGy compared with measurements are: 6.821, 12,469 and 49.600 cGy protocols for 8, 15 and 60 UM. From the obtained series of 2D projections a 3D reconstruction was performed in each case, and the dimensions of the reconstructed structures were compared with actual objects. Conclusion: We have successfully developed within the GATE platform a complete and detailed model of a 160 MLC LINAC with its MV-CBCT flat panel. Future work will consist in simulating epidbased transit dosimetry. http://dx.doi.org/10.1016/j.ejmp.2013.08.072
67 MODELING IN THE LEAKAGE RADIATION OF A MEDICAL LINEAR ACCELERATOR A FUNCTION OF THE COLLIMATOR OPENING: ANALYTICAL EXTRAPOLATION OF THE LEAK FIELD OPENED BY A METHOD SEMI-EMPIRICAL BASED MEASUREMENT AT ZERO FIELD A. Ilias, I. Diallo, J. Bezin. Equipe d’Epidémiologie des Radiations, Centre d’Etudes en Santé des Populations (CESP), UMR 1018 INSERM, Institut de Cancérologie Gustave Roussy, Villejuif, France Introduction: The optimization of radiotherapy requires precise knowledge of all sources at the origin of the radiation, even at low doses to healthy tissues of the patient. Currently, the developed analytical models for estimating the doses to healthy tissue based on the assumption that the radiation leakage from a medical linear accelerator would be independent of the collimator opening. However, this hypothesis does not account for a very large number of physical and geometrical aspects of each accelerator. The objective of this work is to propose a more realistic model for accelerators leaks. Materials and methods: The measurements are performed on a linear accelerator Novalis TxTM (Varian Medical Systems, Palo Alto, CA, USA). Detectors are used thermoluminescent powder type 7 (TLD700) compounds of powder LiF doped with Mg et Ti provided by the company Equal-Estro Laboratory. Development of computer codes using the libraries: CodeBlocksÒ (libraries: OpenGL), MatlabÒ et GnuplotÒ. Results: Concerning theoretical modeling, the early results give encouraging theoretical distributions. The model is the end of development measures analysis is ongoing and results will be presented and discussed. Overall we see a gradual decrease in leakage with increasing the opening of the collimator. This decrease is even more important that we be near the field.
e23
Conclusion: Our model can calculate the dose from accelerator of the leakage for any location in the patient and configuration of irradiation. http://dx.doi.org/10.1016/j.ejmp.2013.08.073
68 VALIDATION OF THE GATE MONTE CARLO CODE FOR RADIATION THERAPY AND APPLICATION TO INHOMOGENEITIES A. Luceski 1, R. Laurent 1, R. Gschwind 1, C. De Conto 1,2. 1 IRMA/LCPR-AC/Chrono-Environnement, UMR CNRS 6249, Université de Franche-Comté, Montbéliard, France, 2 Centre Hospitalier Belfort-Montbéliard, Service d’Oncologie et de Radiothérapie, Site du Mittan, Montbéliard, France Introduction: The treatment planning system (TPS), used in most cases, is based on fast and accurate analytical algorithms for dose estimation. However, limitations appear in inhomogeneous environments with strong gradient of density, as in the lungs. Monte Carlo solutions exist for complicated treatment with high inhomogeneity, such as the gold-standard BEAMnrc/EGSnrc. Nevertheless, the computation times are too long for routine use. In order to implement other Monte Carlo codes for external radiation therapy, our study focuses on the validation of GATE/ GEANT4. Materials and methods: The linear medical accelerator CLINAC 2100C (Varian) from Belfort-Montbéliard hospital is modelised in GATE 6.2 for a 6 MV photon beam. The reference measurements are determined by two types of ionization chambers (PTW 31002 and PTW 31014) and are compared with the results of the both Monte Carlo codes (GATE and BEAMnrc). Once GATE has been validated, the performance of both codes will be evaluated in the inhomogeneities (dentures). Results: The simulation parameters of GATE were adjusted to validate the accelerator modeling from percentage depth dose and profiles in the reference conditions. The results of the both codes with high density inhomogeneities are close. Conclusion: The accelerator model was validated using GATE. The first analyses about the inhomogeneities give promising results. Thereafter, the evaluation of the code will go on more complex models (anthropomorphic phantom, breathing 4D phantom) always using BEAMnrc as a reference. http://dx.doi.org/10.1016/j.ejmp.2013.08.074
69 EXPERIMENTAL STUDY OF THE PERIPHERAL DOSE OUTSIDE THE APPLICATOR FOR ELECTRON BEAMS USED IN THE EXTERNAL RADIOTHERAPY M. Mohamad Alabdoaburas. Institut Gustave Roussy, Villejuif, France Introduction: In electron mode radiotherapy, the scattered radiation by the applicator influence on the dose distribution in the patient inside and outside the treatment field. In this mode, the peripheral dose has two components (without neutron); contamination photons and scattered electrons. In this study we analyze the delivered doses outside applicator electron beams to develop a model for calculating dose outside the applicator for the clinical
e24
Abstracts of the SFPM Annual Meeting 2013 / Physica Medica 29 (2013) e1–e46
research and for the research on the long-term effects of external beam radiotherapy. Methods and materials: The development of the model was based on experimental measurements performed on the two following accelerators: Clinac 2300 C/ D (Varian with applicators Varian type) and Siemens Primus KP2 (with electron applicators EA3). In this study, the measurements of leakage at the applicator surface were performed using an ionization chamber (0.125 cc PTW Semiflex No. 31010 with 4439-type build-up 1 cm) for several energies (6–20 MeV) and field sizes. The dose out of the applicator at the plan patient for the depths of 1 cm and (Rp + 1) cm in the water phantom in function of the lateral distance to the axis of the beam was measured using TLD-700 (Equal-Estro Laboratory, Villejuif, F-94805, France) for several energies and field sizes. the scattered electrons and X-ray components were separated, the measurements at the depth (Rp + 1) cm gives the X-ray component. Results and conclusion: Our preliminary results are encouraging. The Measured leakage is in the range 1–3% of the prescribed dose and in agreement with the literature; it decreases with the distance to the beam axis and increases with the energy and treatment field size. The scattered electrons component is dominant for low energy beams through against the X-ray component increases significantly with energy. http://dx.doi.org/10.1016/j.ejmp.2013.08.075
70 ANALYSIS OF THE IMPACT OF WEDGE FILTERS ON THE DOSE PROFILE SYMMETRY IN EXTERNAL RADIOTHERAPY D. Lemonnier, R. Gschind, M. Diot-Vaschy, F. Tochet, R. Laurent. Université de Franche-Comté, IRMA/LCPR-AC/Chrono-Environnement, UMR CNRS 6249, Montbéliard, France, Service de Radiothérapie, CHRU Jean Minjoz, Besançon, France Context: A bibliographic review, following a symmetry defect discovered on a radiation therapy accelerator, reveals a lack of results on the analysis of asymmetries created on the depth dose profiles with wedge filters. To deal with this issue, we propose an experimental and theoretical study. Material and methods: Measurements of the dose profiles for different wedge angles (15° to 60°) are performed in the reference conditions (SSD = 90 cm, SAD = 100 cm, 10 10 cm2 field), for a 18 MV photon beam with a VARIANÒ 2100C accelerator. Two types of detectors are used: 0.3 cc Semiflex ionization chambers in a PTW MP3 water tank, and a PTW 2D-Array seven29 detector array. These profiles are compared with the data of both TPS Oncentra Master Plan and the Monte-Carlo simulations results, performed with the BEAMnrc code. The combination of multiple wedges is also analysed. Results: The dose profile symmetry differs according to the nature of the filter (physical or dynamic) and depends on experimental conditions, such as the measurement depth or the field size. The combination of two wedges in series (physical and dynamic) has also been modelized. It enables to check that the ‘‘equivalent” wedge angle resulting from these two filters is not a linear combination of these two angles. Conclusion: The results obtained in reference conditions, which should be complemented by a dosimetric evaluation, were used to quantify the symmetry defects in output beams.
http://dx.doi.org/10.1016/j.ejmp.2013.08.076
71 INTENSITY-MODULATED ARC THERAPY USING THE GATE MONTE CARLO SIMULATION PLATFORM IN A GRID ENVIRONMENT B. Lourenço, L. Maigne, Y. Perrot, V. Chassin, D. Donnarieix. Clermont Université, Université Blaise Pascal, LPC, Clermont-Ferrand, France, CNRS/IN2P3, UMR 6533, LPC, Aubière, France, Service de Radiothérapie, Centre Jean Perrin, Clermont-Ferrand, France Introduction: The GATE Monte-Carlo (MC) simulation platform (www.opengatecollaboration.org) based on the GEANT4 toolkit has come into widespread use for simulating Positron Emission Tomography, Single Photon Emission Computed Tomography, Computing Tomography (CT) imaging devices and radiation therapy. In this work, we explore the simulation of an intensity-modulated arc therapy (IMAT) treatment using GATE 6.2. To reach this objective, we first performed a complete modeling of the Varian’s Novalis Tx linear accelerator (15MV photon mode) using the multileaf collimator (MLC). Then, the simulation of the geometry was validated in water before experiencing a head-and-neck cancer treatment. Material and methods: The first stage is to model the Novalis Tx head with the GATE MC platform using manufacturer’s data. We simulated this linac in 15 MV mode and compared depth doses, in-plane and cross-plane profiles with reference measurements (performed with ionization chambers (Semiflex 31013, PTW and LA48 Linear Array, PTW) and PTW 60012 Diode E) in water for several field sizes ranging from 1 1 to 10 10 cm2. Target and flattening filter geometries and initial electron beam are adjusted in order to fit simulation calculations with dose measurements. In a second stage, the MLC geometry implementation enabled the simulation of clinical IMAT treatment plans compared with the iPlan treatment planning software (BrainLab) calculations. In order to reduce the computing time of GATE calculations, the simulations are executed on a distributed infrastructure using the GateLab (http://vip.creatis.insa-lyon.fr/) platform. Results: We show a good agreement between measurements and simulated depth dose profiles in liquid water. GATE and iPlan normalized treatment plans were compared using a gamma index of 2%/mm. The ongoing work concerning treatment plan comparisons demonstrates limits of the iPlan Pencil Beam algorithm close to heterogeneities. Using the distributed infrastructure, space phase file was produced in 14 h for 500 million primary photons generated reaching a gain of a factor 50 comparing to calculations performed on a single CPU. Conclusions: This study demonstrates that GATE offers efficient tools to make possible IMAT applications. In a subsequent work a microdosimetry study should be performed for a complete validation. http://dx.doi.org/10.1016/j.ejmp.2013.08.077
SESSION: NUCLEAR MEDICINE MODERATORS Bardia Farman and Malick Koulibaly REFRESHER COURSE 72 REMINDERS AND STATE OF THE ART ON PET/CT M. Koulibaly. Centre Antoine Lacassagne, Nice, France Abstract not available. http://dx.doi.org/10.1016/j.ejmp.2013.08.078
was focused on the Monte Carlo modeling of such an EPID in order to simulate both planar and 3D CBCT images. Methods: The work presented here follows a preliminary study in which the treatment part of a clinical LINAC (Siemens Oncor) was modeled in GATE v6.2. The objective was to calculate the dose delivered by complex treatments like IMRT. The objective of the study is to extend this model by incorporating the imaging part of the LINAC, which consists of a flat panel detector (Perkin Elmer XRD1640). For this purpose, geometrical and physical data provided by the manufacturer were first accurately modeled in GATE. Assessments of portal imaging were performed by performing dose calculations in a CQ IMRT phantom with GATE for two measurement points with protocols of 8, 15 and 60 UM and comparing the doses with clinical measurements. And with performing 2D CT projections over a 200° arc, 1° increments, and 41 cm 41 cm field of view for homogeneous and heterogeneous structures (introduction of a patient head and neck CT patient). Results: For the calculation of the deposit dose at the isocentre of the CQ IMRT phantom, respectively GATE gave doses of 5.734 0.169, 11.008 0.777 and 46.006 0.711 cGy compared with measurements are: 6.821, 12,469 and 49.600 cGy protocols for 8, 15 and 60 UM. From the obtained series of 2D projections a 3D reconstruction was performed in each case, and the dimensions of the reconstructed structures were compared with actual objects. Conclusion: We have successfully developed within the GATE platform a complete and detailed model of a 160 MLC LINAC with its MV-CBCT flat panel. Future work will consist in simulating epidbased transit dosimetry. http://dx.doi.org/10.1016/j.ejmp.2013.08.072
67 MODELING IN THE LEAKAGE RADIATION OF A MEDICAL LINEAR ACCELERATOR A FUNCTION OF THE COLLIMATOR OPENING: ANALYTICAL EXTRAPOLATION OF THE LEAK FIELD OPENED BY A METHOD SEMI-EMPIRICAL BASED MEASUREMENT AT ZERO FIELD A. Ilias, I. Diallo, J. Bezin. Equipe d’Epidémiologie des Radiations, Centre d’Etudes en Santé des Populations (CESP), UMR 1018 INSERM, Institut de Cancérologie Gustave Roussy, Villejuif, France Introduction: The optimization of radiotherapy requires precise knowledge of all sources at the origin of the radiation, even at low doses to healthy tissues of the patient. Currently, the developed analytical models for estimating the doses to healthy tissue based on the assumption that the radiation leakage from a medical linear accelerator would be independent of the collimator opening. However, this hypothesis does not account for a very large number of physical and geometrical aspects of each accelerator. The objective of this work is to propose a more realistic model for accelerators leaks. Materials and methods: The measurements are performed on a linear accelerator Novalis TxTM (Varian Medical Systems, Palo Alto, CA, USA). Detectors are used thermoluminescent powder type 7 (TLD700) compounds of powder LiF doped with Mg et Ti provided by the company Equal-Estro Laboratory. Development of computer codes using the libraries: CodeBlocksÒ (libraries: OpenGL), MatlabÒ et GnuplotÒ. Results: Concerning theoretical modeling, the early results give encouraging theoretical distributions. The model is the end of development measures analysis is ongoing and results will be presented and discussed. Overall we see a gradual decrease in leakage with increasing the opening of the collimator. This decrease is even more important that we be near the field.
e23
Conclusion: Our model can calculate the dose from accelerator of the leakage for any location in the patient and configuration of irradiation. http://dx.doi.org/10.1016/j.ejmp.2013.08.073
68 VALIDATION OF THE GATE MONTE CARLO CODE FOR RADIATION THERAPY AND APPLICATION TO INHOMOGENEITIES A. Luceski 1, R. Laurent 1, R. Gschwind 1, C. De Conto 1,2. 1 IRMA/LCPR-AC/Chrono-Environnement, UMR CNRS 6249, Université de Franche-Comté, Montbéliard, France, 2 Centre Hospitalier Belfort-Montbéliard, Service d’Oncologie et de Radiothérapie, Site du Mittan, Montbéliard, France Introduction: The treatment planning system (TPS), used in most cases, is based on fast and accurate analytical algorithms for dose estimation. However, limitations appear in inhomogeneous environments with strong gradient of density, as in the lungs. Monte Carlo solutions exist for complicated treatment with high inhomogeneity, such as the gold-standard BEAMnrc/EGSnrc. Nevertheless, the computation times are too long for routine use. In order to implement other Monte Carlo codes for external radiation therapy, our study focuses on the validation of GATE/ GEANT4. Materials and methods: The linear medical accelerator CLINAC 2100C (Varian) from Belfort-Montbéliard hospital is modelised in GATE 6.2 for a 6 MV photon beam. The reference measurements are determined by two types of ionization chambers (PTW 31002 and PTW 31014) and are compared with the results of the both Monte Carlo codes (GATE and BEAMnrc). Once GATE has been validated, the performance of both codes will be evaluated in the inhomogeneities (dentures). Results: The simulation parameters of GATE were adjusted to validate the accelerator modeling from percentage depth dose and profiles in the reference conditions. The results of the both codes with high density inhomogeneities are close. Conclusion: The accelerator model was validated using GATE. The first analyses about the inhomogeneities give promising results. Thereafter, the evaluation of the code will go on more complex models (anthropomorphic phantom, breathing 4D phantom) always using BEAMnrc as a reference. http://dx.doi.org/10.1016/j.ejmp.2013.08.074
69 EXPERIMENTAL STUDY OF THE PERIPHERAL DOSE OUTSIDE THE APPLICATOR FOR ELECTRON BEAMS USED IN THE EXTERNAL RADIOTHERAPY M. Mohamad Alabdoaburas. Institut Gustave Roussy, Villejuif, France Introduction: In electron mode radiotherapy, the scattered radiation by the applicator influence on the dose distribution in the patient inside and outside the treatment field. In this mode, the peripheral dose has two components (without neutron); contamination photons and scattered electrons. In this study we analyze the delivered doses outside applicator electron beams to develop a model for calculating dose outside the applicator for the clinical
e24
Abstracts of the SFPM Annual Meeting 2013 / Physica Medica 29 (2013) e1–e46
research and for the research on the long-term effects of external beam radiotherapy. Methods and materials: The development of the model was based on experimental measurements performed on the two following accelerators: Clinac 2300 C/ D (Varian with applicators Varian type) and Siemens Primus KP2 (with electron applicators EA3). In this study, the measurements of leakage at the applicator surface were performed using an ionization chamber (0.125 cc PTW Semiflex No. 31010 with 4439-type build-up 1 cm) for several energies (6–20 MeV) and field sizes. The dose out of the applicator at the plan patient for the depths of 1 cm and (Rp + 1) cm in the water phantom in function of the lateral distance to the axis of the beam was measured using TLD-700 (Equal-Estro Laboratory, Villejuif, F-94805, France) for several energies and field sizes. the scattered electrons and X-ray components were separated, the measurements at the depth (Rp + 1) cm gives the X-ray component. Results and conclusion: Our preliminary results are encouraging. The Measured leakage is in the range 1–3% of the prescribed dose and in agreement with the literature; it decreases with the distance to the beam axis and increases with the energy and treatment field size. The scattered electrons component is dominant for low energy beams through against the X-ray component increases significantly with energy. http://dx.doi.org/10.1016/j.ejmp.2013.08.075
70 ANALYSIS OF THE IMPACT OF WEDGE FILTERS ON THE DOSE PROFILE SYMMETRY IN EXTERNAL RADIOTHERAPY D. Lemonnier, R. Gschind, M. Diot-Vaschy, F. Tochet, R. Laurent. Université de Franche-Comté, IRMA/LCPR-AC/Chrono-Environnement, UMR CNRS 6249, Montbéliard, France, Service de Radiothérapie, CHRU Jean Minjoz, Besançon, France Context: A bibliographic review, following a symmetry defect discovered on a radiation therapy accelerator, reveals a lack of results on the analysis of asymmetries created on the depth dose profiles with wedge filters. To deal with this issue, we propose an experimental and theoretical study. Material and methods: Measurements of the dose profiles for different wedge angles (15° to 60°) are performed in the reference conditions (SSD = 90 cm, SAD = 100 cm, 10 10 cm2 field), for a 18 MV photon beam with a VARIANÒ 2100C accelerator. Two types of detectors are used: 0.3 cc Semiflex ionization chambers in a PTW MP3 water tank, and a PTW 2D-Array seven29 detector array. These profiles are compared with the data of both TPS Oncentra Master Plan and the Monte-Carlo simulations results, performed with the BEAMnrc code. The combination of multiple wedges is also analysed. Results: The dose profile symmetry differs according to the nature of the filter (physical or dynamic) and depends on experimental conditions, such as the measurement depth or the field size. The combination of two wedges in series (physical and dynamic) has also been modelized. It enables to check that the ‘‘equivalent” wedge angle resulting from these two filters is not a linear combination of these two angles. Conclusion: The results obtained in reference conditions, which should be complemented by a dosimetric evaluation, were used to quantify the symmetry defects in output beams.
http://dx.doi.org/10.1016/j.ejmp.2013.08.076
71 INTENSITY-MODULATED ARC THERAPY USING THE GATE MONTE CARLO SIMULATION PLATFORM IN A GRID ENVIRONMENT B. Lourenço, L. Maigne, Y. Perrot, V. Chassin, D. Donnarieix. Clermont Université, Université Blaise Pascal, LPC, Clermont-Ferrand, France, CNRS/IN2P3, UMR 6533, LPC, Aubière, France, Service de Radiothérapie, Centre Jean Perrin, Clermont-Ferrand, France Introduction: The GATE Monte-Carlo (MC) simulation platform (www.opengatecollaboration.org) based on the GEANT4 toolkit has come into widespread use for simulating Positron Emission Tomography, Single Photon Emission Computed Tomography, Computing Tomography (CT) imaging devices and radiation therapy. In this work, we explore the simulation of an intensity-modulated arc therapy (IMAT) treatment using GATE 6.2. To reach this objective, we first performed a complete modeling of the Varian’s Novalis Tx linear accelerator (15MV photon mode) using the multileaf collimator (MLC). Then, the simulation of the geometry was validated in water before experiencing a head-and-neck cancer treatment. Material and methods: The first stage is to model the Novalis Tx head with the GATE MC platform using manufacturer’s data. We simulated this linac in 15 MV mode and compared depth doses, in-plane and cross-plane profiles with reference measurements (performed with ionization chambers (Semiflex 31013, PTW and LA48 Linear Array, PTW) and PTW 60012 Diode E) in water for several field sizes ranging from 1 1 to 10 10 cm2. Target and flattening filter geometries and initial electron beam are adjusted in order to fit simulation calculations with dose measurements. In a second stage, the MLC geometry implementation enabled the simulation of clinical IMAT treatment plans compared with the iPlan treatment planning software (BrainLab) calculations. In order to reduce the computing time of GATE calculations, the simulations are executed on a distributed infrastructure using the GateLab (http://vip.creatis.insa-lyon.fr/) platform. Results: We show a good agreement between measurements and simulated depth dose profiles in liquid water. GATE and iPlan normalized treatment plans were compared using a gamma index of 2%/mm. The ongoing work concerning treatment plan comparisons demonstrates limits of the iPlan Pencil Beam algorithm close to heterogeneities. Using the distributed infrastructure, space phase file was produced in 14 h for 500 million primary photons generated reaching a gain of a factor 50 comparing to calculations performed on a single CPU. Conclusions: This study demonstrates that GATE offers efficient tools to make possible IMAT applications. In a subsequent work a microdosimetry study should be performed for a complete validation. http://dx.doi.org/10.1016/j.ejmp.2013.08.077
SESSION: NUCLEAR MEDICINE MODERATORS Bardia Farman and Malick Koulibaly REFRESHER COURSE 72 REMINDERS AND STATE OF THE ART ON PET/CT M. Koulibaly. Centre Antoine Lacassagne, Nice, France Abstract not available. http://dx.doi.org/10.1016/j.ejmp.2013.08.078