- Email: [email protected]
Abstract ID: 115 A Monte Carlo-based eigenspectrum decomposition technique for computed tomography
24
Abstracts / Physica Medica 42 (2017) 1–50
an optimal base of materials representing tissue compositions. To ensure robustness against CT noise, the Bayesian estimator is constructed and resolves the maximum a posteriori fraction of eigentissues in each voxel. The performance of the method in deriving proton beam interaction properties is evaluated with dual-energy CT (DECT) data and compared to a state-of-the-art elemental composition parameterization. Comparison is made with several levels of noise and in the presence of statistical variations in tissue composition and density. The performance of the BETD to an arbitrary number of energies is also investigated by simulating CT data with two to five energy bins with equivalent noise levels. Results. Using simulated noise-free CT numbers for 43 reference soft tissues, the BETD and parameterization methods give equivalent results for stopping powers estimation (0.11% and 0.13% respectively). However, when noise and tissue variation are present, the BETD reduces the RMS error on stopping powers from 2.79% for parameterization to 1.88% for the proposed approach. The BETD method also shows potential for using CT with more than 2 energies, where a number of four energy bins is shown to reduce proton beam range uncertainty by a factor of up to 1.5 compared to the parameterization method used with DECT. Conclusion. This work proposes a general approach to determine elemental compositions and density for Monte Carlo inputs using CT data in a clinical context, where noise and tissues variations significantly degrade the performance of currently known methods.
References 1. Paganetti Harald. Phys Med Biol 2012;57(11):R99. 2. Landry Guillaume et al. Med Phys 2010;37(10):5188–98. 3. Lalonde Arthur, Bouchard Hugo. Phys Med Biol 2016;61(22):8044. http://dx.doi.org/10.1016/j.ejmp.2017.09.060
Abstract ID: 114 The impact of dual-energy CT tissue segmentation for low-dose rate prostate brachytherapy Monte Carlo dose calculations Charlotte Remy a,*, Arthur Lalonde b, Hugo Bouchard b,c a
Université de Nantes, Département de Physique, Nantes, France Université de Montréal, Département de Physique, Montréal, Canada c Centre de recherche du CHUM, Montréal, Canada ⇑ Presenting author. b
Purpose. To evaluate the impact of a novel tissue segmentation method based on dual-energy CT (DECT) for low-dose rate (LDR) brachytherapy dose calculations, by comparison with a reference single-energy CT (SECT) segmentation method. Methods. A virtual patient geometry is created using the DICOMRT of a real patient pelvis SECT scan, where known elemental compositions and varying densities are overwritten in each voxel to define a reference phantom. Simulated CT images are generated using XCOM attenuation coefficients, with a 100 kVp spectrum for SECT, and 80 and 140Sn kVp for DECT. Tissue segmentations for Monte Carlo (MC) dose calculations are performed with both SECT and DECT and compared with the reference geometry. For SECT, the method of Schneider et al. [1] is used and for DECT, the eigentissue decomposition of Lalonde & Bouchard [2] used in combination with a Bayesian estimator. A LDR prostate brachytherapy treatment is planned with 125I sources and calculated using the MC code Brachydose for all three cases. Dose distributions and dose-volume histograms (DVH) are compared to the reference dose distribution to investigate the accuracy of the tissue segmentation methods. Results. For noiseless images, DECT-based tissue segmentation outperforms the SECT procedure with a relative dose distribution
root mean square error (RMSE) of 3.08% versus 8.02%, and provides DVH closest to the reference for all tissues. For a medium level of noise (12 HU), Bayesian eigentissue decomposition performs better with a dose calculation RMSE of 6.11% and 8.49% for DECT and SECT, respectively. Both methods yield similar DVHs for the prostate while DECT segmentation remains more accurate for organs at risk. Conclusion. Our study shows that DECT-based tissue segmentation has the potential to provide LDR brachytherapy dose distributions with higher accuracy that conventional SECT in a clinical context, even in the presence of noise.
References 1. Schneider W et al. Correlation between CT numbers and tissue parameters needed for Monte Carlo simulations of clinical dose distributions. Phys Med Biol 2000;45(2):459. 2. Lalonde A, Bouchard H. A general method to derive tissue parameters for Monte Carlo dose calculation with multi-energy CT. Phys Med Biol 2016;61(22):8044. http://dx.doi.org/10.1016/j.ejmp.2017.09.061
Abstract ID: 115 A Monte Carlo-based eigenspectrum decomposition technique for computed tomography Mikaël Simard a,*, Hugo Bouchard a,b a
Université de Montréal, Département de physique, Montréal, Québec, Canada b Centre de recherche du centre hospitaler de l’Université de Montréal, Montréal, Québec, Canada ⇑ Presenting author. Purpose. The characterization of computed tomography (CT) X-ray spectra is important for beam-hardening correction techniques and raw-data reconstruction methods [1,2]. In this work, we propose a novel spectrum estimation approach based on transmission measurements and the use of Monte-Carlo (MC) to generate basis spectra. Methods. The EGSnrc/BEAM MC code is used to generate basis Xray spectra. The XTUBE component module is used to produce bremsstrahlung photon energy spectra from monoenergetic electrons transported through a tungsten target (10°), a beryllium window (1 mm) and additional filtration. To ensure that the modelled spectra cover the features of the unknown spectrum, a total of 40 spectra with various levels of filtration are generated using different thicknesses of aluminum and carbon, ranging from 2 mm to 18 mm. Principal component analysis is performed on the MC-generated model spectra to extract a set of linearly independent basis functions, each called eigenspectrum, which reduces the dimensionality of the problem and allows stable fitting. Transmission measurements of a calibration phantom are simulated using ray-tracing with an 80-kV source and added Poisson noise. The estimated spectrum is expressed as the weighted sum of eigenspectra and reconstructed through a constrained least squares technique. Results. Using 8 eigenspectra, the 80-kV spectrum is reconstructed with a RMS error (RMSE) of 3.8%. The difference between the mean energy of the estimated and true spectrum is 0.01 keV. Reproducing the same methodology for a 140-kV spectrum yields a RMSE of 4.5% and mean energy difference of 0.1 keV. Conclusion. The proposed method is shown promising to accurately characterize X-ray spectra with transmission data. With limited details on the X-ray tube and relying solely on calibration scans, our methodology provides robust spectrum estimation and is promising for reducing the known ill-posedness [3,4] of known transmission-based approaches. Applications of the technique to
Abstracts / Physica Medica 42 (2017) 1–50
CT are expected to improve the accuracy of quantitative imaging for radiotherapy.
References 1. 2. 3. 4.
De Man B. IEEE Trans 2000;20(10). Cai C. Med Phys 2013;40(11). Ali ESM, Rogers DWO. Phys Med Biol 2011;57(1). Zhao W. Phys Med Biol 2014;60(1).
http://dx.doi.org/10.1016/j.ejmp.2017.09.062
Abstract ID: 116 Comparison of beam output factors in MCNP6 and Geant4 based IAEA phase-space files Raquel Ivon Sanchez-Estrada a,*, Enrique Betancourt Garcia a, Arturo Delfin Loya b, Edmundo del Valle Gallegos b a School of Physics and Mathematics, Nuclear Engineering Department, Mexico City, Mexico b National Institute for Nuclear Research, Nuclear Systems Department, Mexico City, Mexico ⇑ Presenting author.
Monte Carlo (MC) dose calculation algorithms demand an accurate characterization of the radiation beam. At present, three MCbased beam models are commonly used for dose calculation; namely, full MC simulation, virtual source model, and phase space (phsp) files. The first two require detailed information of the LINAC head: information that is not always available from vendors. Therefore, properly validated phase-space data for external beam radiotherapy, available from the IAEA Nuclear Data Services section, remains a valuable alternative for MC beam simulation. The aim of this work is to compare the beam output factors obtained by MCbased phsp simulations in MCNP6 and Geant4. The simulations were performed with the photon mode energies of 6, 10, and 25 MV on the ELEKTA Precise. The simulations are divided into two steps: (1) the development of a method for directly reading the phase-space files provided by the IAEA in MCNP6, and (2) the determination of cutoff values, variation reduction techniques, and field size. Patientspecific beam line devices (blocks, jaws, wedges, etc.) were not simulated. The comparison of the output factors as percentage depth dose (PDD), lateral dose profiles, and dose distributions for different field sizes were computed using Geant4 and MCNP6. Both calculations generate matching PDD for a range of open-field sizes within the statistical uncertainties. Variation in lateral dose profiles varies up to 5% in the 25 MV energy mode. Comparison of dose distributions for an open 10 10 field by the gamma evaluation test returns a value of 0.93. Despite the lack of a user-friendly MCNP6 interface, this work shows that MCNP6 is suitable for beam simulation based IAEA-phsp. http://dx.doi.org/10.1016/j.ejmp.2017.09.063
Abstract ID: 118 Internal dosimetry of 68Ga-DOTATATE using Monte Carlo GATE simulation for XCAT phantom Mersede Mokri a, Mohmmad Reza Ay b, Sima Taghizade c, Marzieh Ebrahimi a, Parham Geramifar a a
Research Center For Nuclear Medicine, Shariati Hospital, Tehran University of Medical Sciences, Tehran, Iran b Medical Physics and Biomedical Engineering Department, School of Medicine, Tehran University of Medical Sciences, Tehran, Iran c Research Center for Science and Technology in Medicine, RCSTM, Tehran, Iran
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Introduction. Widespread use of FDG PET/CT imaging leads to improvement in non-FDG- avid somatostatin receptor imaging of tumor tissue. These synthetic somatostatin analogs can be labeled with b-emitting radionuclides, such as 68Ga[1], but estimating the absorbed dose in critical organs is important. The aim of this research is to calculate absorbed dose in all organs especially pituitary gland and thymus in 68 Ga-DOTATATE dosimetry. Materials and Methods. Two total body male and female XCAT phantoms with 128128 matrix size and 600 slices containing 1 mCi activity of 68Ga was simulated. GATE Monte-Carlo code was employed for dosimetry calculations. Based on MIRD schema, we reported s-values of self-absorption and cross-irradiation in spleen, bladder, kidneys and liver, as well as cross-irradiation in pituitary gland and thymus. Results. We reported the S-value for spleen, the most critical organ in 68Ga-DOTATATE to be 13.7e 004 mGy/MBq-s and 15.6e 004 mGy/MBq-s in male and female phantom respectively. The highest amount of cross-irradiation in spleen is from kidney with the amount of 0.097e 004 mGy/MBq-s. The amount of self-absorption is in Bladder with 42.1e 004 mGy/MBq-s and 50e 004 mGy/MBqs in male and female phantom respectively. The absorbed dose in thymus from spleen is 2.3710e 006 mGy/MBq-s in male and 3.1138e 006 mGy/MBq-s in female. Absorbed dose of pituitary gland from spleen is 0.53e 007 mGy/MBq-s. Conclusion. We performed internal dosimetry using XCAT phantoms and GATE Monte-Carlo code for 68Ga. Our results could be helpful in estimating absorbed dose in critical organs specially those not being considered in conventional methods.
References 1. Skoura E et al. The impact of 68Ga-DOTATATE PET/CT imaging on management of patients with neuroendocrine tumors: experience from a national referral center in the United Kingdom. J Nucl Med 2016;57(1):34–40. http://dx.doi.org/10.1016/j.ejmp.2017.09.064
Abstract ID: 122 Verification of dose estimation for Monte-Carlo based treatment planning system for boron neutron capture therapy Hiroaki Kumada a,*, Kenta Takada b, Teruhito Aihara a, Akira Matsumura a, Hideyuki Sakurai a, Takeji Sakae a a
University of Tsukuba, Faculty of Medicine, Tsukuba, Japan University of Tsukuba Hospital, Proton Medical Research Center, Tsukuba, Japan ⇑ Presenting author. b
University of Tsukuba is developing a treatment device for accelerator-based for boron neutron capture therapy (BNCT). In the project, not only the treatment device (neutron source) but also several peripheral devices requiring in BNCT treatment [1]. As part of the development, a Monte-Carlo based treatment planning system (Developing code: Tsukuba-Plan) applicable to BNCT is also being developed. Regarding Monte-Carlo dose calculation engine, the Tsukuba-Plan has employed PHITS as the multi-purpose Monte Carlo Particle and Heavy Ion Transport code System. PHITS allows to calculate behaviors for several radiations such as neutrons, photons, protons and heavy-ions [2]. Therefore the Tsukuba-Plan with PHITS enables to perform dose estimation for not only BNCT but also particle radiotherapy and X-ray therapy. A prototype of the Tsukuba plan has been completed. At present, we are carrying out several verifications for the Tsukuba-Plan.
Abstracts / Physica Medica 42 (2017) 1–50
an optimal base of materials representing tissue compositions. To ensure robustness against CT noise, the Bayesian estimator is constructed and resolves the maximum a posteriori fraction of eigentissues in each voxel. The performance of the method in deriving proton beam interaction properties is evaluated with dual-energy CT (DECT) data and compared to a state-of-the-art elemental composition parameterization. Comparison is made with several levels of noise and in the presence of statistical variations in tissue composition and density. The performance of the BETD to an arbitrary number of energies is also investigated by simulating CT data with two to five energy bins with equivalent noise levels. Results. Using simulated noise-free CT numbers for 43 reference soft tissues, the BETD and parameterization methods give equivalent results for stopping powers estimation (0.11% and 0.13% respectively). However, when noise and tissue variation are present, the BETD reduces the RMS error on stopping powers from 2.79% for parameterization to 1.88% for the proposed approach. The BETD method also shows potential for using CT with more than 2 energies, where a number of four energy bins is shown to reduce proton beam range uncertainty by a factor of up to 1.5 compared to the parameterization method used with DECT. Conclusion. This work proposes a general approach to determine elemental compositions and density for Monte Carlo inputs using CT data in a clinical context, where noise and tissues variations significantly degrade the performance of currently known methods.
References 1. Paganetti Harald. Phys Med Biol 2012;57(11):R99. 2. Landry Guillaume et al. Med Phys 2010;37(10):5188–98. 3. Lalonde Arthur, Bouchard Hugo. Phys Med Biol 2016;61(22):8044. http://dx.doi.org/10.1016/j.ejmp.2017.09.060
Abstract ID: 114 The impact of dual-energy CT tissue segmentation for low-dose rate prostate brachytherapy Monte Carlo dose calculations Charlotte Remy a,*, Arthur Lalonde b, Hugo Bouchard b,c a
Université de Nantes, Département de Physique, Nantes, France Université de Montréal, Département de Physique, Montréal, Canada c Centre de recherche du CHUM, Montréal, Canada ⇑ Presenting author. b
Purpose. To evaluate the impact of a novel tissue segmentation method based on dual-energy CT (DECT) for low-dose rate (LDR) brachytherapy dose calculations, by comparison with a reference single-energy CT (SECT) segmentation method. Methods. A virtual patient geometry is created using the DICOMRT of a real patient pelvis SECT scan, where known elemental compositions and varying densities are overwritten in each voxel to define a reference phantom. Simulated CT images are generated using XCOM attenuation coefficients, with a 100 kVp spectrum for SECT, and 80 and 140Sn kVp for DECT. Tissue segmentations for Monte Carlo (MC) dose calculations are performed with both SECT and DECT and compared with the reference geometry. For SECT, the method of Schneider et al. [1] is used and for DECT, the eigentissue decomposition of Lalonde & Bouchard [2] used in combination with a Bayesian estimator. A LDR prostate brachytherapy treatment is planned with 125I sources and calculated using the MC code Brachydose for all three cases. Dose distributions and dose-volume histograms (DVH) are compared to the reference dose distribution to investigate the accuracy of the tissue segmentation methods. Results. For noiseless images, DECT-based tissue segmentation outperforms the SECT procedure with a relative dose distribution
root mean square error (RMSE) of 3.08% versus 8.02%, and provides DVH closest to the reference for all tissues. For a medium level of noise (12 HU), Bayesian eigentissue decomposition performs better with a dose calculation RMSE of 6.11% and 8.49% for DECT and SECT, respectively. Both methods yield similar DVHs for the prostate while DECT segmentation remains more accurate for organs at risk. Conclusion. Our study shows that DECT-based tissue segmentation has the potential to provide LDR brachytherapy dose distributions with higher accuracy that conventional SECT in a clinical context, even in the presence of noise.
References 1. Schneider W et al. Correlation between CT numbers and tissue parameters needed for Monte Carlo simulations of clinical dose distributions. Phys Med Biol 2000;45(2):459. 2. Lalonde A, Bouchard H. A general method to derive tissue parameters for Monte Carlo dose calculation with multi-energy CT. Phys Med Biol 2016;61(22):8044. http://dx.doi.org/10.1016/j.ejmp.2017.09.061
Abstract ID: 115 A Monte Carlo-based eigenspectrum decomposition technique for computed tomography Mikaël Simard a,*, Hugo Bouchard a,b a
Université de Montréal, Département de physique, Montréal, Québec, Canada b Centre de recherche du centre hospitaler de l’Université de Montréal, Montréal, Québec, Canada ⇑ Presenting author. Purpose. The characterization of computed tomography (CT) X-ray spectra is important for beam-hardening correction techniques and raw-data reconstruction methods [1,2]. In this work, we propose a novel spectrum estimation approach based on transmission measurements and the use of Monte-Carlo (MC) to generate basis spectra. Methods. The EGSnrc/BEAM MC code is used to generate basis Xray spectra. The XTUBE component module is used to produce bremsstrahlung photon energy spectra from monoenergetic electrons transported through a tungsten target (10°), a beryllium window (1 mm) and additional filtration. To ensure that the modelled spectra cover the features of the unknown spectrum, a total of 40 spectra with various levels of filtration are generated using different thicknesses of aluminum and carbon, ranging from 2 mm to 18 mm. Principal component analysis is performed on the MC-generated model spectra to extract a set of linearly independent basis functions, each called eigenspectrum, which reduces the dimensionality of the problem and allows stable fitting. Transmission measurements of a calibration phantom are simulated using ray-tracing with an 80-kV source and added Poisson noise. The estimated spectrum is expressed as the weighted sum of eigenspectra and reconstructed through a constrained least squares technique. Results. Using 8 eigenspectra, the 80-kV spectrum is reconstructed with a RMS error (RMSE) of 3.8%. The difference between the mean energy of the estimated and true spectrum is 0.01 keV. Reproducing the same methodology for a 140-kV spectrum yields a RMSE of 4.5% and mean energy difference of 0.1 keV. Conclusion. The proposed method is shown promising to accurately characterize X-ray spectra with transmission data. With limited details on the X-ray tube and relying solely on calibration scans, our methodology provides robust spectrum estimation and is promising for reducing the known ill-posedness [3,4] of known transmission-based approaches. Applications of the technique to
Abstracts / Physica Medica 42 (2017) 1–50
CT are expected to improve the accuracy of quantitative imaging for radiotherapy.
References 1. 2. 3. 4.
De Man B. IEEE Trans 2000;20(10). Cai C. Med Phys 2013;40(11). Ali ESM, Rogers DWO. Phys Med Biol 2011;57(1). Zhao W. Phys Med Biol 2014;60(1).
http://dx.doi.org/10.1016/j.ejmp.2017.09.062
Abstract ID: 116 Comparison of beam output factors in MCNP6 and Geant4 based IAEA phase-space files Raquel Ivon Sanchez-Estrada a,*, Enrique Betancourt Garcia a, Arturo Delfin Loya b, Edmundo del Valle Gallegos b a School of Physics and Mathematics, Nuclear Engineering Department, Mexico City, Mexico b National Institute for Nuclear Research, Nuclear Systems Department, Mexico City, Mexico ⇑ Presenting author.
Monte Carlo (MC) dose calculation algorithms demand an accurate characterization of the radiation beam. At present, three MCbased beam models are commonly used for dose calculation; namely, full MC simulation, virtual source model, and phase space (phsp) files. The first two require detailed information of the LINAC head: information that is not always available from vendors. Therefore, properly validated phase-space data for external beam radiotherapy, available from the IAEA Nuclear Data Services section, remains a valuable alternative for MC beam simulation. The aim of this work is to compare the beam output factors obtained by MCbased phsp simulations in MCNP6 and Geant4. The simulations were performed with the photon mode energies of 6, 10, and 25 MV on the ELEKTA Precise. The simulations are divided into two steps: (1) the development of a method for directly reading the phase-space files provided by the IAEA in MCNP6, and (2) the determination of cutoff values, variation reduction techniques, and field size. Patientspecific beam line devices (blocks, jaws, wedges, etc.) were not simulated. The comparison of the output factors as percentage depth dose (PDD), lateral dose profiles, and dose distributions for different field sizes were computed using Geant4 and MCNP6. Both calculations generate matching PDD for a range of open-field sizes within the statistical uncertainties. Variation in lateral dose profiles varies up to 5% in the 25 MV energy mode. Comparison of dose distributions for an open 10 10 field by the gamma evaluation test returns a value of 0.93. Despite the lack of a user-friendly MCNP6 interface, this work shows that MCNP6 is suitable for beam simulation based IAEA-phsp. http://dx.doi.org/10.1016/j.ejmp.2017.09.063
Abstract ID: 118 Internal dosimetry of 68Ga-DOTATATE using Monte Carlo GATE simulation for XCAT phantom Mersede Mokri a, Mohmmad Reza Ay b, Sima Taghizade c, Marzieh Ebrahimi a, Parham Geramifar a a
Research Center For Nuclear Medicine, Shariati Hospital, Tehran University of Medical Sciences, Tehran, Iran b Medical Physics and Biomedical Engineering Department, School of Medicine, Tehran University of Medical Sciences, Tehran, Iran c Research Center for Science and Technology in Medicine, RCSTM, Tehran, Iran
25
Introduction. Widespread use of FDG PET/CT imaging leads to improvement in non-FDG- avid somatostatin receptor imaging of tumor tissue. These synthetic somatostatin analogs can be labeled with b-emitting radionuclides, such as 68Ga[1], but estimating the absorbed dose in critical organs is important. The aim of this research is to calculate absorbed dose in all organs especially pituitary gland and thymus in 68 Ga-DOTATATE dosimetry. Materials and Methods. Two total body male and female XCAT phantoms with 128128 matrix size and 600 slices containing 1 mCi activity of 68Ga was simulated. GATE Monte-Carlo code was employed for dosimetry calculations. Based on MIRD schema, we reported s-values of self-absorption and cross-irradiation in spleen, bladder, kidneys and liver, as well as cross-irradiation in pituitary gland and thymus. Results. We reported the S-value for spleen, the most critical organ in 68Ga-DOTATATE to be 13.7e 004 mGy/MBq-s and 15.6e 004 mGy/MBq-s in male and female phantom respectively. The highest amount of cross-irradiation in spleen is from kidney with the amount of 0.097e 004 mGy/MBq-s. The amount of self-absorption is in Bladder with 42.1e 004 mGy/MBq-s and 50e 004 mGy/MBqs in male and female phantom respectively. The absorbed dose in thymus from spleen is 2.3710e 006 mGy/MBq-s in male and 3.1138e 006 mGy/MBq-s in female. Absorbed dose of pituitary gland from spleen is 0.53e 007 mGy/MBq-s. Conclusion. We performed internal dosimetry using XCAT phantoms and GATE Monte-Carlo code for 68Ga. Our results could be helpful in estimating absorbed dose in critical organs specially those not being considered in conventional methods.
References 1. Skoura E et al. The impact of 68Ga-DOTATATE PET/CT imaging on management of patients with neuroendocrine tumors: experience from a national referral center in the United Kingdom. J Nucl Med 2016;57(1):34–40. http://dx.doi.org/10.1016/j.ejmp.2017.09.064
Abstract ID: 122 Verification of dose estimation for Monte-Carlo based treatment planning system for boron neutron capture therapy Hiroaki Kumada a,*, Kenta Takada b, Teruhito Aihara a, Akira Matsumura a, Hideyuki Sakurai a, Takeji Sakae a a
University of Tsukuba, Faculty of Medicine, Tsukuba, Japan University of Tsukuba Hospital, Proton Medical Research Center, Tsukuba, Japan ⇑ Presenting author. b
University of Tsukuba is developing a treatment device for accelerator-based for boron neutron capture therapy (BNCT). In the project, not only the treatment device (neutron source) but also several peripheral devices requiring in BNCT treatment [1]. As part of the development, a Monte-Carlo based treatment planning system (Developing code: Tsukuba-Plan) applicable to BNCT is also being developed. Regarding Monte-Carlo dose calculation engine, the Tsukuba-Plan has employed PHITS as the multi-purpose Monte Carlo Particle and Heavy Ion Transport code System. PHITS allows to calculate behaviors for several radiations such as neutrons, photons, protons and heavy-ions [2]. Therefore the Tsukuba-Plan with PHITS enables to perform dose estimation for not only BNCT but also particle radiotherapy and X-ray therapy. A prototype of the Tsukuba plan has been completed. At present, we are carrying out several verifications for the Tsukuba-Plan.