- Email: [email protected]
Abstract ID: 88 Quantum versus classical Monte Carlo simulation of low energy electron transport in condensed media
18
Abstracts / Physica Medica 42 (2017) 1–50
b
LMU Munich, Department of Radiation Oncology, Munich, Germany Université de Lyon, CREATIS, CNRS UMR5220 Inserm U1206, INSALyon, University Lyon 1, F69373 Lyon, France ⇑ Presenting author. c
The adoption of cone beam computed tomography (CBCT) image guidance in proton therapy has spurred research on CBCT image correction for dose calculation. Initially, methods based on deformable image registration gained attention [1], however projection correction approaches based on prior CT information[2] have been shown to perform well for several body sites [3]. The shading correction algorithm used in [2,3] relies on image processing of the subtraction of digitally reconstructed radiographs (DRR) of a DIR-registered prior CT, and CBCT projections. In this study we have performed Monte Carlo (MC) simulation of CBCT imaging to disentangle the different sources of projection degradation, and to evaluate the physicality of the shading correction. The GATE MC toolkit’s fixed-forced-detection actor was employed, along with source and detector models optimized for an Elekta XVI CBCT system, to simulate CBCT imaging of an electron density phantom. The shading correction algorithm was applied to the measured projections and the so-called scatter component (SCA) was compared to the MC simulated scatter. Measured and simulated CBCT projections (scatter + primary) agreed well, with the largest discrepancy found for a bone insert (3% of log transformed projections). Important disagreement was observed with the MC scatter signal when the contribution from beam hardening was kept in the SCA. Undoing the beam hardening correction from the SCA using functions derived from MC primary projections and DRRs greatly improved agreement of scatter signals from MC and SCA (3% on average), with the largest discrepancy found for the bone insert (12%). Residual discrepancies were shown to stem from the intrinsic limitations of the SCA. Proton therapy dose calculations on corrected CBCT will be presented in addition to the results above.
References 1. Landry G et al. Investigating CT to CBCT image registration for head and neck proton therapy as a tool for daily dose recalculation. Med Phys 2015;42:1354–66. 2. Park YK et al. Proton dose calculation on scatter-corrected CBCT image: feasibility study for adaptive proton therapy. Med Phys 2015;42:4449–59. 3. Kurz C et al. Investigating deformable image registration and scatter correction for CBCT-based dose calculation in adaptive IMPT. Med Phys 2016;43:5635–46. http://dx.doi.org/10.1016/j.ejmp.2017.09.044
Abstract ID: 87 Brachytherapy source and applicator models for diverse Monte Carlo simulations with egs_brachy Rowan M. Thomson a,*, Marc J.P. Chamberland a,b, Stephen G. Deering a, D.W.O. Rogers a, Randle E.P. Taylor a a
Carleton University, Department of Physics, Ottawa, Canada BC Cancer Agency – Vancouver Centre, Vancouver, Canada ⇑ Presenting author. b
Purpose. To describe the development and benchmarking of a library of brachytherapy sources and applicators for use with egs_brachy, a new open-source code for brachytherapy calculations. Methods. egs_brachy is a modern EGSnrc application employing the EGSnrc C++ class library (egs++) [1]. The extended egs++ framework (new geometry and shape classes developed with egs_brachy)
is used to construct detailed models of sources and applicators. Source models are constructed for 52 photon brachytherapy sources (radionuclides Pd-103, I-125, Cs-131, Cs-137, Ir-192, Yb-169, and Co60). A generic miniature X-ray tube source is modeled. Eye plaque applicators include 10–24 mm diameter Collaborative Ocular Melanoma Study (COMS) plaques (containing I-125 or Pd-103 seeds) and BEBIG Ru-106 beta-emitting plaques (diameters 11.6– 25.4 mm). The generic high-dose rate (HDR) Ir-192 shielded applicator of the AAPM-ESTRO-ABG Working Group on Dose Calculation Algorithms for Brachytherapy (WG-DCAB) is modeled. Dose distributions and TG-43 parameters (photon sources only) computed with egs_brachy are compared with published values. Results. For photon (radionuclide) sources, dose-rate constant, radial dose function, and anisotropy function values are generally in excellent agreement with published values [2]. Miniature X-ray tube results for egs_brachy agree with BrachyDose results within statistical uncertainties. Ocular plaque dose distributions show excellent agreement with published values. For COMS plaques, egs_brachy results agree with BrachyDose and MCNP5 published values within uncertainties <1% in the tumour [3]. For Ru-106 betaemitting plaques, egs_brachy results agree within sub-2% uncertainties with PENELOPE results [4], and this agreement is notable due to the historically poor agreement between results from different publications. Dose distributions about the WG-DCAB applicator agree with results from other MC codes. Conclusions. egs_brachy can model diverse source and applicator models and dose distributions are in excellent agreement with published values, demonstrating the code’s versatility and accuracy. Source and applicator models will be included in future egs_brachy distributions.
References 1. Chamberland et al. Phys Med Biol 2016;61:8214–31. 2. Taylor, Rogers. Med Phys 2008;35:4228–41. 3. Thomson et al, Med. Phys. 2008;35:5530–5543; Melhus, Rivard, Med. Phys. 2008;35:3364-3371. 4. Hermida-Lopez M. Med Phys 2013;40:101705. http://dx.doi.org/10.1016/j.ejmp.2017.09.045
Abstract ID: 88 Quantum versus classical Monte Carlo simulation of low energy electron transport in condensed media Rowan M. Thomson a,*, Iwan Kawrakow b a
Carleton University, Department of Physics, Ottawa, Canada ViewRay Inc, Cleveland, USA ⇑ Presenting author. b
Purpose. Monte Carlo simulations are being applied to study radiation interactions and energy deposition on sub-micron length scales within cells, e.g., DNA, in diverse contexts across medical physics. While these classical trajectory Monte Carlo simulations ignore the quantum wave nature of the electron, quantum effects may become non-negligible as electron energy decreases below 1 keV, with electron wavelength becoming considerable relative to the size of biological targets. This work investigates quantum mechanical (QM) treatments of low energy electron transport in condensed media and compares results with those from the corresponding classical trajectory Monte Carlo (MC) model. Methods. For QM calculations, a simplified model of electron transport in water is developed consisting of a plane wave (representing an electron) incident on a collection of 103 point scatterers (molecules) representing a water droplet. Scatterer positions are
Abstracts / Physica Medica 42 (2017) 1–50
random but are constrained by a minimum scatterer-to-scatterer separation, dmin, in some simulations. Cross sections for isotropic elastic and inelastic (absorption) interactions are varied. QM calculations involve numerically solving the system of 103 coupled equations for the electron wavefield incident on each scatterer. Results are averaged over 105 droplets with different point scatterer positions but otherwise same parameters (incident electron energy, cross sections). Average QM droplet incoherent cross sections and scattering event densities are compared with analogues computed within the corresponding classical MC model, and estimates of relative errors on MC results are computed. Results. Relative errors on MC results vary with electron wavelength, droplet shape and structure (dmin), and interaction cross section. Relative errors on droplet differential cross sections generally differ from errors on scattering event density. The introduction of inelastic scatter generally increases relative errors (compared to calculations with the same elastic scatter cross section) with some exceptions (e.g. longer wavelength, relatively large inelastic cross section). Accounting for structure (non-zero dmin) enhances differences between QM and MC results. Conclusions. The quantum wave nature of electrons may be nonnegligible for simulations of electron transport within small-scale biological targets. Future work will involve the development of more realistic models of electron transport in condensed media. http://dx.doi.org/10.1016/j.ejmp.2017.09.046
Abstract ID: 89 Investigation of conformal arc therapy utilizing Cobalt 60 beams Ahmed Eldib a, Grisel Mora b, Omar Chibani a, Charlie Ma a,* a
Fox Chase Cancer Centre, Department of Radiation Oncology, Philadelphia, USA b Institute of Biophysics and Biomedical Engineering, Faculty of Sciences University of Lisbon, Lisbon, Portugal ⇑ Presenting author. Purpose. The trend today in modern radiation therapy is toward conformal therapy with segmented or moving field techniques. Generally, this requires multifield irradiation or the use of arc/rotation therapy. Many authors have pointed out in literature that if the Co-60 machines were modernized with state of the art devices, it may be able to provide similar quality of radiation therapy as provided by linacs. Co-60 units will have the advantage of having more simple and robust design, and minimal maintenance and technical expertise to operate the machine as compared to the technologically complex linacs. Thus, in this work we conduct a dosimetric comparison between conformal arc utilizing Co-60 beams and that utilizing 6MV beam energy. Material and methods. CT scans was unarchived for patient previously treated by SBRT in our department. We selected lung, breast, and head and neck cases. All of these cases were previously planned on Eclipse planning system (Varian, Palo Alto, Medical Systems). We regenerated treatment plans using conformal arcs with the arc being modeled by delivery of multiple conformal beams. Dose distributions for all plans were calculated using Monte Carlo simulation for both 6MV and Co-60 beam energies. Results. As the number of fields increases, advantage of higher energies over lower radiation energies decreases. In all studied cases, conformal arc plans utilizing Co-60 beam was achieving almost same conformity when compared to the 6Mv plans. Isodose distributions were tailored similarly around the PTV. On reviewing the minimum and maximum dose reaching all targets, it was shown that both Co60 and 6Mv plans was achieving our clinical acceptation criteria for the target coverage. The DVH of Co-60 plans were showing slightly
19
lower dose to critical structures however the difference was small in most cases. Conclusion. Our results have shown the potential for newly designed Co-60 machines as a modality that could treat a good fraction of cancer patients. The overall performance seen in the conformal arcs using Co-60 beams was encouraging as being compared to the 6MV conformal arcs. There was no significant superiority detected for the 6MV plans over the Co-60 plans for SBRT cases. http://dx.doi.org/10.1016/j.ejmp.2017.09.047
Abstract ID: 90 Accounting for radiation-induced indirect damage on DNA with the GEANT4 code Liset de la Fuente Rosales *, Mario A. Bernal Rodriguez Institute of Physics Gleb Wataghin – Unicamp, Applied Physics Department, Campinas, Brazil ⇑ Presenting author. The use of Monte Carlo (MC) simulations remains a powerful tool to study biological effects induced by ionizing radiations on living beings. Several MC codes, with different level of complexity, are commonly used in research fields such as nanodosimetry, radiotherapy, radiation protection, and space radiation. This work performed an upgrade of an existing model developed by Bernal et al. [1] for radiobiological purposes, for accounting for the indirect DNA damage produced by ionizing particles. The Geant4-DNA simulation toolkit was used to simulate physical, pre-chemical and chemical stages of the early DNA damage induced by protons. Liquid water was used as the medium for simulations. Two phase-space files were generated, one containing energy deposition events inside the region of interest (ROI), and another one with the position of chemical species produced by water radiolysis from 0.1 ps up to 1 ns. The information contained in both files was superposed on a genetic material model with atomic-resolution,consisting of several copies of 30-nm chromatin fibers. The B-DNA configuration was used. This work focused on the indirect damage produced by the hydroxyl radical (OH.) at the deoxy-ribose sugar sites, normally trough hydrogen abstraction. Corresponding damage yields were determined. The approach followed to account for indirect damage in DNA was the same used by other radiobiological codes [2,3]. The critical parameter considered here was the reaction radius, which was calculated from the Smoluchowski’s diffusion equation. Single, double, and total strand break yields produced by direct, indirect, and mixed mechanisms are reported.
References 1. Bernal M, Sikansi D, Cavalcante F, Incerti S, Champion C, Ivachenko V, Francis Z. An atomistic geometrical model of the B-DNA configuration for DNA-radiation interaction simulations. Comput Phys Commun 2013;184:2840–7. 2. Karamitros M, Luan S, Bernal M, Allison J, Baldacchino G, Davidkova M, Francis Z, Friedland W, Ivantchenko V, Ivantchenko A, Mantero A, Nieminem P, Santin G, Tran HN, Stepan V, Incerti S. Diffusion-controlled reactions modeling in Geant4-DNA. J Comput Phys 2014;274:841–82. 3. Buxton G, Greenstock C, Helman P, Ross A. Critical review of rate constants for reactions of hydrated electrons, hydrogen atoms and hydroxyl radicals in aqueous solution. J Phys Chem Ref Data 1988;17:513–886. http://dx.doi.org/10.1016/j.ejmp.2017.09.048
Abstracts / Physica Medica 42 (2017) 1–50
b
LMU Munich, Department of Radiation Oncology, Munich, Germany Université de Lyon, CREATIS, CNRS UMR5220 Inserm U1206, INSALyon, University Lyon 1, F69373 Lyon, France ⇑ Presenting author. c
The adoption of cone beam computed tomography (CBCT) image guidance in proton therapy has spurred research on CBCT image correction for dose calculation. Initially, methods based on deformable image registration gained attention [1], however projection correction approaches based on prior CT information[2] have been shown to perform well for several body sites [3]. The shading correction algorithm used in [2,3] relies on image processing of the subtraction of digitally reconstructed radiographs (DRR) of a DIR-registered prior CT, and CBCT projections. In this study we have performed Monte Carlo (MC) simulation of CBCT imaging to disentangle the different sources of projection degradation, and to evaluate the physicality of the shading correction. The GATE MC toolkit’s fixed-forced-detection actor was employed, along with source and detector models optimized for an Elekta XVI CBCT system, to simulate CBCT imaging of an electron density phantom. The shading correction algorithm was applied to the measured projections and the so-called scatter component (SCA) was compared to the MC simulated scatter. Measured and simulated CBCT projections (scatter + primary) agreed well, with the largest discrepancy found for a bone insert (3% of log transformed projections). Important disagreement was observed with the MC scatter signal when the contribution from beam hardening was kept in the SCA. Undoing the beam hardening correction from the SCA using functions derived from MC primary projections and DRRs greatly improved agreement of scatter signals from MC and SCA (3% on average), with the largest discrepancy found for the bone insert (12%). Residual discrepancies were shown to stem from the intrinsic limitations of the SCA. Proton therapy dose calculations on corrected CBCT will be presented in addition to the results above.
References 1. Landry G et al. Investigating CT to CBCT image registration for head and neck proton therapy as a tool for daily dose recalculation. Med Phys 2015;42:1354–66. 2. Park YK et al. Proton dose calculation on scatter-corrected CBCT image: feasibility study for adaptive proton therapy. Med Phys 2015;42:4449–59. 3. Kurz C et al. Investigating deformable image registration and scatter correction for CBCT-based dose calculation in adaptive IMPT. Med Phys 2016;43:5635–46. http://dx.doi.org/10.1016/j.ejmp.2017.09.044
Abstract ID: 87 Brachytherapy source and applicator models for diverse Monte Carlo simulations with egs_brachy Rowan M. Thomson a,*, Marc J.P. Chamberland a,b, Stephen G. Deering a, D.W.O. Rogers a, Randle E.P. Taylor a a
Carleton University, Department of Physics, Ottawa, Canada BC Cancer Agency – Vancouver Centre, Vancouver, Canada ⇑ Presenting author. b
Purpose. To describe the development and benchmarking of a library of brachytherapy sources and applicators for use with egs_brachy, a new open-source code for brachytherapy calculations. Methods. egs_brachy is a modern EGSnrc application employing the EGSnrc C++ class library (egs++) [1]. The extended egs++ framework (new geometry and shape classes developed with egs_brachy)
is used to construct detailed models of sources and applicators. Source models are constructed for 52 photon brachytherapy sources (radionuclides Pd-103, I-125, Cs-131, Cs-137, Ir-192, Yb-169, and Co60). A generic miniature X-ray tube source is modeled. Eye plaque applicators include 10–24 mm diameter Collaborative Ocular Melanoma Study (COMS) plaques (containing I-125 or Pd-103 seeds) and BEBIG Ru-106 beta-emitting plaques (diameters 11.6– 25.4 mm). The generic high-dose rate (HDR) Ir-192 shielded applicator of the AAPM-ESTRO-ABG Working Group on Dose Calculation Algorithms for Brachytherapy (WG-DCAB) is modeled. Dose distributions and TG-43 parameters (photon sources only) computed with egs_brachy are compared with published values. Results. For photon (radionuclide) sources, dose-rate constant, radial dose function, and anisotropy function values are generally in excellent agreement with published values [2]. Miniature X-ray tube results for egs_brachy agree with BrachyDose results within statistical uncertainties. Ocular plaque dose distributions show excellent agreement with published values. For COMS plaques, egs_brachy results agree with BrachyDose and MCNP5 published values within uncertainties <1% in the tumour [3]. For Ru-106 betaemitting plaques, egs_brachy results agree within sub-2% uncertainties with PENELOPE results [4], and this agreement is notable due to the historically poor agreement between results from different publications. Dose distributions about the WG-DCAB applicator agree with results from other MC codes. Conclusions. egs_brachy can model diverse source and applicator models and dose distributions are in excellent agreement with published values, demonstrating the code’s versatility and accuracy. Source and applicator models will be included in future egs_brachy distributions.
References 1. Chamberland et al. Phys Med Biol 2016;61:8214–31. 2. Taylor, Rogers. Med Phys 2008;35:4228–41. 3. Thomson et al, Med. Phys. 2008;35:5530–5543; Melhus, Rivard, Med. Phys. 2008;35:3364-3371. 4. Hermida-Lopez M. Med Phys 2013;40:101705. http://dx.doi.org/10.1016/j.ejmp.2017.09.045
Abstract ID: 88 Quantum versus classical Monte Carlo simulation of low energy electron transport in condensed media Rowan M. Thomson a,*, Iwan Kawrakow b a
Carleton University, Department of Physics, Ottawa, Canada ViewRay Inc, Cleveland, USA ⇑ Presenting author. b
Purpose. Monte Carlo simulations are being applied to study radiation interactions and energy deposition on sub-micron length scales within cells, e.g., DNA, in diverse contexts across medical physics. While these classical trajectory Monte Carlo simulations ignore the quantum wave nature of the electron, quantum effects may become non-negligible as electron energy decreases below 1 keV, with electron wavelength becoming considerable relative to the size of biological targets. This work investigates quantum mechanical (QM) treatments of low energy electron transport in condensed media and compares results with those from the corresponding classical trajectory Monte Carlo (MC) model. Methods. For QM calculations, a simplified model of electron transport in water is developed consisting of a plane wave (representing an electron) incident on a collection of 103 point scatterers (molecules) representing a water droplet. Scatterer positions are
Abstracts / Physica Medica 42 (2017) 1–50
random but are constrained by a minimum scatterer-to-scatterer separation, dmin, in some simulations. Cross sections for isotropic elastic and inelastic (absorption) interactions are varied. QM calculations involve numerically solving the system of 103 coupled equations for the electron wavefield incident on each scatterer. Results are averaged over 105 droplets with different point scatterer positions but otherwise same parameters (incident electron energy, cross sections). Average QM droplet incoherent cross sections and scattering event densities are compared with analogues computed within the corresponding classical MC model, and estimates of relative errors on MC results are computed. Results. Relative errors on MC results vary with electron wavelength, droplet shape and structure (dmin), and interaction cross section. Relative errors on droplet differential cross sections generally differ from errors on scattering event density. The introduction of inelastic scatter generally increases relative errors (compared to calculations with the same elastic scatter cross section) with some exceptions (e.g. longer wavelength, relatively large inelastic cross section). Accounting for structure (non-zero dmin) enhances differences between QM and MC results. Conclusions. The quantum wave nature of electrons may be nonnegligible for simulations of electron transport within small-scale biological targets. Future work will involve the development of more realistic models of electron transport in condensed media. http://dx.doi.org/10.1016/j.ejmp.2017.09.046
Abstract ID: 89 Investigation of conformal arc therapy utilizing Cobalt 60 beams Ahmed Eldib a, Grisel Mora b, Omar Chibani a, Charlie Ma a,* a
Fox Chase Cancer Centre, Department of Radiation Oncology, Philadelphia, USA b Institute of Biophysics and Biomedical Engineering, Faculty of Sciences University of Lisbon, Lisbon, Portugal ⇑ Presenting author. Purpose. The trend today in modern radiation therapy is toward conformal therapy with segmented or moving field techniques. Generally, this requires multifield irradiation or the use of arc/rotation therapy. Many authors have pointed out in literature that if the Co-60 machines were modernized with state of the art devices, it may be able to provide similar quality of radiation therapy as provided by linacs. Co-60 units will have the advantage of having more simple and robust design, and minimal maintenance and technical expertise to operate the machine as compared to the technologically complex linacs. Thus, in this work we conduct a dosimetric comparison between conformal arc utilizing Co-60 beams and that utilizing 6MV beam energy. Material and methods. CT scans was unarchived for patient previously treated by SBRT in our department. We selected lung, breast, and head and neck cases. All of these cases were previously planned on Eclipse planning system (Varian, Palo Alto, Medical Systems). We regenerated treatment plans using conformal arcs with the arc being modeled by delivery of multiple conformal beams. Dose distributions for all plans were calculated using Monte Carlo simulation for both 6MV and Co-60 beam energies. Results. As the number of fields increases, advantage of higher energies over lower radiation energies decreases. In all studied cases, conformal arc plans utilizing Co-60 beam was achieving almost same conformity when compared to the 6Mv plans. Isodose distributions were tailored similarly around the PTV. On reviewing the minimum and maximum dose reaching all targets, it was shown that both Co60 and 6Mv plans was achieving our clinical acceptation criteria for the target coverage. The DVH of Co-60 plans were showing slightly
19
lower dose to critical structures however the difference was small in most cases. Conclusion. Our results have shown the potential for newly designed Co-60 machines as a modality that could treat a good fraction of cancer patients. The overall performance seen in the conformal arcs using Co-60 beams was encouraging as being compared to the 6MV conformal arcs. There was no significant superiority detected for the 6MV plans over the Co-60 plans for SBRT cases. http://dx.doi.org/10.1016/j.ejmp.2017.09.047
Abstract ID: 90 Accounting for radiation-induced indirect damage on DNA with the GEANT4 code Liset de la Fuente Rosales *, Mario A. Bernal Rodriguez Institute of Physics Gleb Wataghin – Unicamp, Applied Physics Department, Campinas, Brazil ⇑ Presenting author. The use of Monte Carlo (MC) simulations remains a powerful tool to study biological effects induced by ionizing radiations on living beings. Several MC codes, with different level of complexity, are commonly used in research fields such as nanodosimetry, radiotherapy, radiation protection, and space radiation. This work performed an upgrade of an existing model developed by Bernal et al. [1] for radiobiological purposes, for accounting for the indirect DNA damage produced by ionizing particles. The Geant4-DNA simulation toolkit was used to simulate physical, pre-chemical and chemical stages of the early DNA damage induced by protons. Liquid water was used as the medium for simulations. Two phase-space files were generated, one containing energy deposition events inside the region of interest (ROI), and another one with the position of chemical species produced by water radiolysis from 0.1 ps up to 1 ns. The information contained in both files was superposed on a genetic material model with atomic-resolution,consisting of several copies of 30-nm chromatin fibers. The B-DNA configuration was used. This work focused on the indirect damage produced by the hydroxyl radical (OH.) at the deoxy-ribose sugar sites, normally trough hydrogen abstraction. Corresponding damage yields were determined. The approach followed to account for indirect damage in DNA was the same used by other radiobiological codes [2,3]. The critical parameter considered here was the reaction radius, which was calculated from the Smoluchowski’s diffusion equation. Single, double, and total strand break yields produced by direct, indirect, and mixed mechanisms are reported.
References 1. Bernal M, Sikansi D, Cavalcante F, Incerti S, Champion C, Ivachenko V, Francis Z. An atomistic geometrical model of the B-DNA configuration for DNA-radiation interaction simulations. Comput Phys Commun 2013;184:2840–7. 2. Karamitros M, Luan S, Bernal M, Allison J, Baldacchino G, Davidkova M, Francis Z, Friedland W, Ivantchenko V, Ivantchenko A, Mantero A, Nieminem P, Santin G, Tran HN, Stepan V, Incerti S. Diffusion-controlled reactions modeling in Geant4-DNA. J Comput Phys 2014;274:841–82. 3. Buxton G, Greenstock C, Helman P, Ross A. Critical review of rate constants for reactions of hydrated electrons, hydrogen atoms and hydroxyl radicals in aqueous solution. J Phys Chem Ref Data 1988;17:513–886. http://dx.doi.org/10.1016/j.ejmp.2017.09.048