Journal Articles
2020
Model-Based Dose Calculation Algorithms for Brachytherapy Dosimetry Journal Article
In: Seminars in Radiation Oncology, vol. 30, no. 1, pp. 77–86, 2020, ISSN: 1532-9461.
@article{enger_model-based_2020,
title = {Model-Based Dose Calculation Algorithms for Brachytherapy Dosimetry},
author = {Shirin A. Enger and Javier Vijande and Mark J. Rivard},
doi = {10.1016/j.semradonc.2019.08.006},
issn = {1532-9461},
year = {2020},
date = {2020-01-01},
journal = {Seminars in Radiation Oncology},
volume = {30},
number = {1},
pages = {77--86},
abstract = {The purpose of this study was to review the limitations of dose calculation formalisms for photon-emitting brachytherapy sources based on the American Association of Physicists in Medicine (AAPM) Task Group No. 43 (TG-43) report and to provide recommendations to transition to model-based dose calculation algorithms. Additionally, an overview of these algorithms and approaches is presented. The influence of tissue and seed/applicator heterogeneities on brachytherapy dose distributions for breast, gynecologic, head and neck, rectum, and prostate cancers as well as eye plaques and electronic brachytherapy treatments were investigated by comparing dose calculations based on the TG-43 formalism and model-based dose calculation algorithms.},
keywords = {Algorithms, Brachytherapy, Computer-Assisted, Female, Humans, Male, Medical, Models, Neoplasms, Photons, Practice Guidelines as Topic, Radiometry, Radiotherapy Dosage, Radiotherapy Planning, Societies, Theoretical},
pubstate = {published},
tppubtype = {article}
}
The purpose of this study was to review the limitations of dose calculation formalisms for photon-emitting brachytherapy sources based on the American Association of Physicists in Medicine (AAPM) Task Group No. 43 (TG-43) report and to provide recommendations to transition to model-based dose calculation algorithms. Additionally, an overview of these algorithms and approaches is presented. The influence of tissue and seed/applicator heterogeneities on brachytherapy dose distributions for breast, gynecologic, head and neck, rectum, and prostate cancers as well as eye plaques and electronic brachytherapy treatments were investigated by comparing dose calculations based on the TG-43 formalism and model-based dose calculation algorithms.2017
Microdosimetry calculations for monoenergetic electrons using Geant4-DNA combined with a weighted track sampling algorithm Journal Article
In: Physics in Medicine and Biology, vol. 62, no. 13, pp. 5495–5508, 2017, ISSN: 1361-6560.
@article{famulari_microdosimetry_2017,
title = {Microdosimetry calculations for monoenergetic electrons using Geant4-DNA combined with a weighted track sampling algorithm},
author = {Gabriel Famulari and Piotr Pater and Shirin A. Enger},
doi = {10.1088/1361-6560/aa71f6},
issn = {1361-6560},
year = {2017},
date = {2017-07-01},
journal = {Physics in Medicine and Biology},
volume = {62},
number = {13},
pages = {5495--5508},
abstract = {The aim of this study was to calculate microdosimetric distributions for low energy electrons simulated using the Monte Carlo track structure code Geant4-DNA. Tracks for monoenergetic electrons with kinetic energies ranging from 100 eV to 1 MeV were simulated in an infinite spherical water phantom using the Geant4-DNA extension included in Geant4 toolkit version 10.2 (patch 02). The microdosimetric distributions were obtained through random sampling of transfer points and overlaying scoring volumes within the associated volume of the tracks. Relative frequency distributions of energy deposition f(textgreaterE)/f(textgreater0) and dose mean lineal energy ([Formula: see text]) values were calculated in nanometer-sized spherical and cylindrical targets. The effects of scoring volume and scoring techniques were examined. The results were compared with published data generated using MOCA8B and KURBUC. Geant4-DNA produces a lower frequency of higher energy deposits than MOCA8B. The [Formula: see text] values calculated with Geant4-DNA are smaller than those calculated using MOCA8B and KURBUC. The differences are mainly due to the lower ionization and excitation cross sections of Geant4-DNA for low energy electrons. To a lesser extent, discrepancies can also be attributed to the implementation in this study of a new and fast scoring technique that differs from that used in previous studies. For the same mean chord length ([Formula: see text]), the [Formula: see text] calculated in cylindrical volumes are larger than those calculated in spherical volumes. The discrepancies due to cross sections and scoring geometries increase with decreasing scoring site dimensions. A new set of [Formula: see text] values has been presented for monoenergetic electrons using a fast track sampling algorithm and the most recent physics models implemented in Geant4-DNA. This dataset can be combined with primary electron spectra to predict the radiation quality of photon and electron beams.},
keywords = {Algorithms, DNA, DNA Damage, Electrons, Imaging, Monte Carlo Method, Phantoms, Photons, Radiometry},
pubstate = {published},
tppubtype = {article}
}
The aim of this study was to calculate microdosimetric distributions for low energy electrons simulated using the Monte Carlo track structure code Geant4-DNA. Tracks for monoenergetic electrons with kinetic energies ranging from 100 eV to 1 MeV were simulated in an infinite spherical water phantom using the Geant4-DNA extension included in Geant4 toolkit version 10.2 (patch 02). The microdosimetric distributions were obtained through random sampling of transfer points and overlaying scoring volumes within the associated volume of the tracks. Relative frequency distributions of energy deposition f(textgreaterE)/f(textgreater0) and dose mean lineal energy ([Formula: see text]) values were calculated in nanometer-sized spherical and cylindrical targets. The effects of scoring volume and scoring techniques were examined. The results were compared with published data generated using MOCA8B and KURBUC. Geant4-DNA produces a lower frequency of higher energy deposits than MOCA8B. The [Formula: see text] values calculated with Geant4-DNA are smaller than those calculated using MOCA8B and KURBUC. The differences are mainly due to the lower ionization and excitation cross sections of Geant4-DNA for low energy electrons. To a lesser extent, discrepancies can also be attributed to the implementation in this study of a new and fast scoring technique that differs from that used in previous studies. For the same mean chord length ([Formula: see text]), the [Formula: see text] calculated in cylindrical volumes are larger than those calculated in spherical volumes. The discrepancies due to cross sections and scoring geometries increase with decreasing scoring site dimensions. A new set of [Formula: see text] values has been presented for monoenergetic electrons using a fast track sampling algorithm and the most recent physics models implemented in Geant4-DNA. This dataset can be combined with primary electron spectra to predict the radiation quality of photon and electron beams.2016
A brachytherapy photon radiation quality index Q(BT) for probe-type dosimetry Journal Article
In: Physica medica: PM: an international journal devoted to the applications of physics to medicine and biology: official journal of the Italian Association of Biomedical Physics (AIFB), vol. 32, no. 6, pp. 741–748, 2016, ISSN: 1724-191X.
@article{quast_brachytherapy_2016,
title = {A brachytherapy photon radiation quality index Q(BT) for probe-type dosimetry},
author = {Ulrich Quast and Theodor W. Kaulich and José T. Álvarez-Romero and Sa Carlsson Tedgren and Shirin A. Enger and David C. Medich and Firas Mourtada and Jose Perez-Calatayud and Mark J. Rivard and G. Abu Zakaria},
doi = {10.1016/j.ejmp.2016.03.008},
issn = {1724-191X},
year = {2016},
date = {2016-06-01},
journal = {Physica medica: PM: an international journal devoted to the applications of physics to medicine and biology: official journal of the Italian Association of Biomedical Physics (AIFB)},
volume = {32},
number = {6},
pages = {741--748},
abstract = {INTRODUCTION: In photon brachytherapy (BT), experimental dosimetry is needed to verify treatment plans if planning algorithms neglect varying attenuation, absorption or scattering conditions. The detector's response is energy dependent, including the detector material to water dose ratio and the intrinsic mechanisms. The local mean photon energy E¯(r) must be known or another equivalent energy quality parameter used. We propose the brachytherapy photon radiation quality indexQ(BT)(E¯), to characterize the photon radiation quality in view of measurements of distributions of the absorbed dose to water, Dw, around BT sources. MATERIALS AND METHODS: While the external photon beam radiotherapy (EBRT) radiation quality index Q(EBRT)(E¯)=TPR10(20)(E¯) is not applicable to BT, the authors have applied a novel energy dependent parameter, called brachytherapy photon radiation quality index, defined as Q(BT)(E¯)=Dprim(r=2cm,θ0=90°)/Dprim(r0=1cm,θ0=90°), utilizing precise primary absorbed dose data, Dprim, from source reference databases, without additional MC-calculations. RESULTS AND DISCUSSION: For BT photon sources used clinically, Q(BT)(E¯) enables to determine the effective mean linear attenuation coefficient μ¯(E) and thus the effective energy of the primary photons Eprim(eff)(r0,θ0) at the TG-43 reference position Pref(r0=1cm,θ0=90°), being close to the mean total photon energy E¯tot(r0,θ0). If one has calibrated detectors, published E¯tot(r) and the BT radiation quality correction factor [Formula: see text] for different BT radiation qualities Q and Q0, the detector's response can be determined and Dw(r,θ) measured in the vicinity of BT photon sources.
CONCLUSIONS: This novel brachytherapy photon radiation quality indexQ(BT) characterizes sufficiently accurate and precise the primary photon's penetration probability and scattering potential.},
keywords = {Absorbed dose to water, Brachytherapy, Detector response, Effective energy, Photon brachytherapy radiation quality index, Photons, Radiation, Radiometry, Scattering, Uncertainty},
pubstate = {published},
tppubtype = {article}
}
INTRODUCTION: In photon brachytherapy (BT), experimental dosimetry is needed to verify treatment plans if planning algorithms neglect varying attenuation, absorption or scattering conditions. The detector’s response is energy dependent, including the detector material to water dose ratio and the intrinsic mechanisms. The local mean photon energy E¯(r) must be known or another equivalent energy quality parameter used. We propose the brachytherapy photon radiation quality indexQ(BT)(E¯), to characterize the photon radiation quality in view of measurements of distributions of the absorbed dose to water, Dw, around BT sources. MATERIALS AND METHODS: While the external photon beam radiotherapy (EBRT) radiation quality index Q(EBRT)(E¯)=TPR10(20)(E¯) is not applicable to BT, the authors have applied a novel energy dependent parameter, called brachytherapy photon radiation quality index, defined as Q(BT)(E¯)=Dprim(r=2cm,θ0=90°)/Dprim(r0=1cm,θ0=90°), utilizing precise primary absorbed dose data, Dprim, from source reference databases, without additional MC-calculations. RESULTS AND DISCUSSION: For BT photon sources used clinically, Q(BT)(E¯) enables to determine the effective mean linear attenuation coefficient μ¯(E) and thus the effective energy of the primary photons Eprim(eff)(r0,θ0) at the TG-43 reference position Pref(r0=1cm,θ0=90°), being close to the mean total photon energy E¯tot(r0,θ0). If one has calibrated detectors, published E¯tot(r) and the BT radiation quality correction factor [Formula: see text] for different BT radiation qualities Q and Q0, the detector’s response can be determined and Dw(r,θ) measured in the vicinity of BT photon sources.
CONCLUSIONS: This novel brachytherapy photon radiation quality indexQ(BT) characterizes sufficiently accurate and precise the primary photon’s penetration probability and scattering potential.2013
Gadolinium-153 as a brachytherapy isotope Journal Article
In: Physics in Medicine and Biology, vol. 58, no. 4, pp. 957–964, 2013, ISSN: 1361-6560.
@article{enger_gadolinium-153_2013,
title = {Gadolinium-153 as a brachytherapy isotope},
author = {Shirin A. Enger and Darrell R. Fisher and Ryan T. Flynn},
doi = {10.1088/0031-9155/58/4/957},
issn = {1361-6560},
year = {2013},
date = {2013-02-01},
journal = {Physics in Medicine and Biology},
volume = {58},
number = {4},
pages = {957--964},
abstract = {The purpose of this work was to present the fundamental dosimetric characteristics of a hypothetical (153)Gd brachytherapy source using the AAPM TG-43U1 dose-calculation formalism. Gadolinium-153 is an intermediate-energy isotope that emits 40-100 keV photons with a half-life of 242 days. The rationale for considering (153)Gd as a brachytherapy source is for its potential of patient specific shielding and to enable reduced personnel shielding requirements relative to (192)Ir, and as an isotope for interstitial rotating shield brachytherapy (I-RSBT). A hypothetical (153)Gd brachytherapy source with an active core of 0.84 mm diameter, 10 mm length and specific activity of 5.55 TBq of (153)Gd per gram of Gd was simulated with Geant4. The encapsulation material was stainless steel with a thickness of 0.08 mm. The radial dose function, anisotropy function and photon spectrum in water were calculated for the (153)Gd source. The simulated (153)Gd source had an activity of 242 GBq and a dose rate in water 1 cm off axis of 13.12 Gy h(-1), indicating that it would be suitable as a low-dose-rate or pulsed-dose-rate brachytherapy source. The beta particles emitted have low enough energies to be absorbed in the source encapsulation. Gadolinium-153 has an increasing radial dose function due to multiple scatter of low-energy photons. Scattered photon dose takes over with distance from the source and contributes to the majority of the absorbed dose. The anisotropy function of the (153)Gd source decreases at low polar angles, as a result of the long active core. The source is less anisotropic at polar angles away from the longitudinal axes. The anisotropy function increases with increasing distance. The (153)Gd source considered would be suitable as an intermediate-energy low-dose-rate or pulsed-dose-rate brachytherapy source. The source could provide a means for I-RSBT delivery and enable brachytherapy treatments with patient specific shielding and reduced personnel shielding requirements relative to (192)Ir.},
keywords = {Anisotropy, Brachytherapy, Equipment Design, Gadolinium, Humans, Iridium Radioisotopes, Male, Monte Carlo Method, Photons, Prostatic Neoplasms, Radiation, Radiation Protection, Radioisotopes, Radiotherapy Dosage, Scattering},
pubstate = {published},
tppubtype = {article}
}
The purpose of this work was to present the fundamental dosimetric characteristics of a hypothetical (153)Gd brachytherapy source using the AAPM TG-43U1 dose-calculation formalism. Gadolinium-153 is an intermediate-energy isotope that emits 40-100 keV photons with a half-life of 242 days. The rationale for considering (153)Gd as a brachytherapy source is for its potential of patient specific shielding and to enable reduced personnel shielding requirements relative to (192)Ir, and as an isotope for interstitial rotating shield brachytherapy (I-RSBT). A hypothetical (153)Gd brachytherapy source with an active core of 0.84 mm diameter, 10 mm length and specific activity of 5.55 TBq of (153)Gd per gram of Gd was simulated with Geant4. The encapsulation material was stainless steel with a thickness of 0.08 mm. The radial dose function, anisotropy function and photon spectrum in water were calculated for the (153)Gd source. The simulated (153)Gd source had an activity of 242 GBq and a dose rate in water 1 cm off axis of 13.12 Gy h(-1), indicating that it would be suitable as a low-dose-rate or pulsed-dose-rate brachytherapy source. The beta particles emitted have low enough energies to be absorbed in the source encapsulation. Gadolinium-153 has an increasing radial dose function due to multiple scatter of low-energy photons. Scattered photon dose takes over with distance from the source and contributes to the majority of the absorbed dose. The anisotropy function of the (153)Gd source decreases at low polar angles, as a result of the long active core. The source is less anisotropic at polar angles away from the longitudinal axes. The anisotropy function increases with increasing distance. The (153)Gd source considered would be suitable as an intermediate-energy low-dose-rate or pulsed-dose-rate brachytherapy source. The source could provide a means for I-RSBT delivery and enable brachytherapy treatments with patient specific shielding and reduced personnel shielding requirements relative to (192)Ir.2012
Dose to tissue medium or water cavities as surrogate for the dose to cell nuclei at brachytherapy photon energies Journal Article
In: Physics in Medicine and Biology, vol. 57, no. 14, pp. 4489–4500, 2012, ISSN: 1361-6560.
@article{enger_dose_2012,
title = {Dose to tissue medium or water cavities as surrogate for the dose to cell nuclei at brachytherapy photon energies},
author = {Shirin A. Enger and Anders Ahnesjö and Frank Verhaegen and Luc Beaulieu},
doi = {10.1088/0031-9155/57/14/4489},
issn = {1361-6560},
year = {2012},
date = {2012-07-01},
journal = {Physics in Medicine and Biology},
volume = {57},
number = {14},
pages = {4489--4500},
abstract = {It has been suggested that modern dose calculation algorithms should be able to report absorbed dose both as dose to the local medium, D(m,m,) and as dose to a water cavity embedded in the medium, D(w,m), using conversion factors from cavity theory. Assuming that the cell nucleus with its DNA content is the most important target for biological response, the aim of this study is to investigate, by means of Monte Carlo (MC) simulations, the relationship of the dose to a cell nucleus in a medium, D(n,m,) to D(m,m) and D(w,m), for different combinations of cell nucleus compositions and tissue media for different photon energies used in brachytherapy. As D(n,m) is very impractical to calculate directly for routine treatment planning, while D(m,m) and D(w,m) are much easier to obtain, the questions arise which one of these quantities is the best surrogate for D(n,m) and which cavity theory assumptions should one use for its estimate. The Geant4.9.4 MC code was used to calculate D(m,m,) D(w,m) and D(n,m) for photon energies from 20 (representing the lower energy end of brachytherapy for ¹⁰³Pd or ¹²⁵I) to 300 keV (close to the mean energy of (¹⁹²Ir) and for the tissue media adipose, breast, prostate and muscle. To simulate the cell and its nucleus, concentric spherical cavities were placed inside a cubic phantom (10 × 10 × 10 mm³). The diameter of the simulated nuclei was set to 14 µm. For each tissue medium, three different setups were simulated; (a) D(n,m) was calculated with nuclei embedded in tissues (MC-D(n,m)). Four different published elemental compositions of cell nuclei were used. (b) D(w,m) was calculated with MC (MC-D(w,m)) and compared with large cavity theory calculated D(w,m) (LCT-D(w,m)), and small cavity theory calculated D(w,m) (SCT-D(w,m)). (c) D(m,m) was calculated with MC (MC-D(m,m)). MC-D(w,m) is a good substitute for MC-D(n,m) for all photon energies and for all simulated nucleus compositions and tissue types. SCT-D(w,m) can be used for most energies in brachytherapy, while LCT-D(w,m) should only be considered for source spectra well below 50 keV, since contributions to the absorbed dose inside the nucleus to a large degree stem from electrons released in the surrounding medium. MC-D(m,m) is not an appropriate substitute for MC-D(n,m) for the lowest photon energies for adipose and breast tissues. The ratio of MC-D(m,m) to MC-D(n,m) for adipose and breast tissue deviates from unity by 34% and 15% respectively for the lowest photon energy (20 keV), whereas the ratio is close to unity for higher energies. For prostate and muscle tissue MC-D(m,m) is a good substitute for MC-D(n,m). However, for all photon energies and tissue types the nucleus composition with the highest hydrogen content behaves differently than other compositions. Elemental compositions of the tissue and nuclei affect considerably the absorbed dose to the cell nuclei for brachytherapy sources, in particular those at the low-energy end of the spectrum. Thus, there is a need for more accurate data for the elemental compositions of tumours and healthy cells. For the nucleus compositions and tissue types investigated, MC-D(w,m) is a good substitute to MC-D(n,m) for all simulated photon energies. Whether other studied surrogates are good approximations to MC-D(n,m) depends on the target size, target composition, composition of the surrounding tissue and photon energy.},
keywords = {Brachytherapy, Cell Line, Cell Nucleus, Humans, Monte Carlo Method, Photons, Radiation Dosage, Radiotherapy Dosage, Water},
pubstate = {published},
tppubtype = {article}
}
It has been suggested that modern dose calculation algorithms should be able to report absorbed dose both as dose to the local medium, D(m,m,) and as dose to a water cavity embedded in the medium, D(w,m), using conversion factors from cavity theory. Assuming that the cell nucleus with its DNA content is the most important target for biological response, the aim of this study is to investigate, by means of Monte Carlo (MC) simulations, the relationship of the dose to a cell nucleus in a medium, D(n,m,) to D(m,m) and D(w,m), for different combinations of cell nucleus compositions and tissue media for different photon energies used in brachytherapy. As D(n,m) is very impractical to calculate directly for routine treatment planning, while D(m,m) and D(w,m) are much easier to obtain, the questions arise which one of these quantities is the best surrogate for D(n,m) and which cavity theory assumptions should one use for its estimate. The Geant4.9.4 MC code was used to calculate D(m,m,) D(w,m) and D(n,m) for photon energies from 20 (representing the lower energy end of brachytherapy for ¹⁰³Pd or ¹²⁵I) to 300 keV (close to the mean energy of (¹⁹²Ir) and for the tissue media adipose, breast, prostate and muscle. To simulate the cell and its nucleus, concentric spherical cavities were placed inside a cubic phantom (10 × 10 × 10 mm³). The diameter of the simulated nuclei was set to 14 µm. For each tissue medium, three different setups were simulated; (a) D(n,m) was calculated with nuclei embedded in tissues (MC-D(n,m)). Four different published elemental compositions of cell nuclei were used. (b) D(w,m) was calculated with MC (MC-D(w,m)) and compared with large cavity theory calculated D(w,m) (LCT-D(w,m)), and small cavity theory calculated D(w,m) (SCT-D(w,m)). (c) D(m,m) was calculated with MC (MC-D(m,m)). MC-D(w,m) is a good substitute for MC-D(n,m) for all photon energies and for all simulated nucleus compositions and tissue types. SCT-D(w,m) can be used for most energies in brachytherapy, while LCT-D(w,m) should only be considered for source spectra well below 50 keV, since contributions to the absorbed dose inside the nucleus to a large degree stem from electrons released in the surrounding medium. MC-D(m,m) is not an appropriate substitute for MC-D(n,m) for the lowest photon energies for adipose and breast tissues. The ratio of MC-D(m,m) to MC-D(n,m) for adipose and breast tissue deviates from unity by 34% and 15% respectively for the lowest photon energy (20 keV), whereas the ratio is close to unity for higher energies. For prostate and muscle tissue MC-D(m,m) is a good substitute for MC-D(n,m). However, for all photon energies and tissue types the nucleus composition with the highest hydrogen content behaves differently than other compositions. Elemental compositions of the tissue and nuclei affect considerably the absorbed dose to the cell nuclei for brachytherapy sources, in particular those at the low-energy end of the spectrum. Thus, there is a need for more accurate data for the elemental compositions of tumours and healthy cells. For the nucleus compositions and tissue types investigated, MC-D(w,m) is a good substitute to MC-D(n,m) for all simulated photon energies. Whether other studied surrogates are good approximations to MC-D(n,m) depends on the target size, target composition, composition of the surrounding tissue and photon energy.2011
Modeling a hypothetical 170Tm source for brachytherapy applications Journal Article
In: Medical Physics, vol. 38, no. 10, pp. 5307–5310, 2011, ISSN: 0094-2405.
@article{enger_modeling_2011,
title = {Modeling a hypothetical 170Tm source for brachytherapy applications},
author = {Shirin A. Enger and Michel D'Amours and Luc Beaulieu},
doi = {10.1118/1.3626482},
issn = {0094-2405},
year = {2011},
date = {2011-10-01},
journal = {Medical Physics},
volume = {38},
number = {10},
pages = {5307--5310},
abstract = {PURPOSE: To perform absorbed dose calculations based on Monte Carlo simulations for a hypothetical (170)Tm source and to investigate the influence of encapsulating material on the energy spectrum of the emitted electrons and photons.
METHODS: GEANT4 Monte Carlo code version 9.2 patch 2 was used to simulate the decay process of (170)Tm and to calculate the absorbed dose distribution using the GEANT4 Penelope physics models. A hypothetical (170)Tm source based on the Flexisource brachytherapy design with the active core set as a pure thulium cylinder (length 3.5 mm and diameter 0.6 mm) and different cylindrical source encapsulations (length 5 mm and thickness 0.125 mm) constructed of titanium, stainless-steel, gold, or platinum were simulated. The radial dose function for the line source approximation was calculated following the TG-43U1 formalism for the stainless-steel encapsulation.
RESULTS: For the titanium and stainless-steel encapsulation, 94% of the total bremsstrahlung is produced inside the core, 4.8 and 5.5% in titanium and stainless-steel capsules, respectively, and less than 1% in water. For the gold capsule, 85% is produced inside the core, 14.2% inside the gold capsule, and a negligible amount (textless1%) in water. Platinum encapsulation resulted in bremsstrahlung effects similar to those with the gold encapsulation. The range of the beta particles decreases by 1.1 mm with the stainless-steel encapsulation compared to the bare source but the tissue will still receive dose from the beta particles several millimeters from the source capsule. The gold and platinum capsules not only absorb most of the electrons but also attenuate low energy photons. The mean energy of the photons escaping the core and the stainless-steel capsule is 113 keV while for the gold and platinum the mean energy is 160 keV and 165 keV, respectively.
CONCLUSIONS: A (170)Tm source is primarily a bremsstrahlung source, with the majority of bremsstrahlung photons being generated in the source core and experiencing little attenuation in the source encapsulation. Electrons are efficiently absorbed by the gold and platinum encapsulations. However, for the stainless-steel capsule (or other lower Z encapsulations) electrons will escape. The dose from these electrons is dominant over the photon dose in the first few millimeter but is not taken into account by current standard treatment planning systems. The total energy spectrum of photons emerging from the source depends on the encapsulation composition and results in mean photon energies well above 100 keV. This is higher than the main gamma-ray energy peak at 84 keV. Based on our results, the use of (170)Tm as a brachytherapy source presents notable challenges.},
keywords = {Algorithms, Brachytherapy, Computer Simulation, Computer-Assisted, Electrons, Equipment Design, Gold, Humans, Models, Monte Carlo Method, Photons, Platinum, Radioisotopes, Radiotherapy Planning, Stainless Steel, Theoretical, Thulium, Titanium},
pubstate = {published},
tppubtype = {article}
}
PURPOSE: To perform absorbed dose calculations based on Monte Carlo simulations for a hypothetical (170)Tm source and to investigate the influence of encapsulating material on the energy spectrum of the emitted electrons and photons.
METHODS: GEANT4 Monte Carlo code version 9.2 patch 2 was used to simulate the decay process of (170)Tm and to calculate the absorbed dose distribution using the GEANT4 Penelope physics models. A hypothetical (170)Tm source based on the Flexisource brachytherapy design with the active core set as a pure thulium cylinder (length 3.5 mm and diameter 0.6 mm) and different cylindrical source encapsulations (length 5 mm and thickness 0.125 mm) constructed of titanium, stainless-steel, gold, or platinum were simulated. The radial dose function for the line source approximation was calculated following the TG-43U1 formalism for the stainless-steel encapsulation.
RESULTS: For the titanium and stainless-steel encapsulation, 94% of the total bremsstrahlung is produced inside the core, 4.8 and 5.5% in titanium and stainless-steel capsules, respectively, and less than 1% in water. For the gold capsule, 85% is produced inside the core, 14.2% inside the gold capsule, and a negligible amount (textless1%) in water. Platinum encapsulation resulted in bremsstrahlung effects similar to those with the gold encapsulation. The range of the beta particles decreases by 1.1 mm with the stainless-steel encapsulation compared to the bare source but the tissue will still receive dose from the beta particles several millimeters from the source capsule. The gold and platinum capsules not only absorb most of the electrons but also attenuate low energy photons. The mean energy of the photons escaping the core and the stainless-steel capsule is 113 keV while for the gold and platinum the mean energy is 160 keV and 165 keV, respectively.
CONCLUSIONS: A (170)Tm source is primarily a bremsstrahlung source, with the majority of bremsstrahlung photons being generated in the source core and experiencing little attenuation in the source encapsulation. Electrons are efficiently absorbed by the gold and platinum encapsulations. However, for the stainless-steel capsule (or other lower Z encapsulations) electrons will escape. The dose from these electrons is dominant over the photon dose in the first few millimeter but is not taken into account by current standard treatment planning systems. The total energy spectrum of photons emerging from the source depends on the encapsulation composition and results in mean photon energies well above 100 keV. This is higher than the main gamma-ray energy peak at 84 keV. Based on our results, the use of (170)Tm as a brachytherapy source presents notable challenges.
Journal Articles
2020
Model-Based Dose Calculation Algorithms for Brachytherapy Dosimetry Journal Article
In: Seminars in Radiation Oncology, vol. 30, no. 1, pp. 77–86, 2020, ISSN: 1532-9461.
@article{enger_model-based_2020,
title = {Model-Based Dose Calculation Algorithms for Brachytherapy Dosimetry},
author = {Shirin A. Enger and Javier Vijande and Mark J. Rivard},
doi = {10.1016/j.semradonc.2019.08.006},
issn = {1532-9461},
year = {2020},
date = {2020-01-01},
journal = {Seminars in Radiation Oncology},
volume = {30},
number = {1},
pages = {77--86},
abstract = {The purpose of this study was to review the limitations of dose calculation formalisms for photon-emitting brachytherapy sources based on the American Association of Physicists in Medicine (AAPM) Task Group No. 43 (TG-43) report and to provide recommendations to transition to model-based dose calculation algorithms. Additionally, an overview of these algorithms and approaches is presented. The influence of tissue and seed/applicator heterogeneities on brachytherapy dose distributions for breast, gynecologic, head and neck, rectum, and prostate cancers as well as eye plaques and electronic brachytherapy treatments were investigated by comparing dose calculations based on the TG-43 formalism and model-based dose calculation algorithms.},
keywords = {Algorithms, Brachytherapy, Computer-Assisted, Female, Humans, Male, Medical, Models, Neoplasms, Photons, Practice Guidelines as Topic, Radiometry, Radiotherapy Dosage, Radiotherapy Planning, Societies, Theoretical},
pubstate = {published},
tppubtype = {article}
}
The purpose of this study was to review the limitations of dose calculation formalisms for photon-emitting brachytherapy sources based on the American Association of Physicists in Medicine (AAPM) Task Group No. 43 (TG-43) report and to provide recommendations to transition to model-based dose calculation algorithms. Additionally, an overview of these algorithms and approaches is presented. The influence of tissue and seed/applicator heterogeneities on brachytherapy dose distributions for breast, gynecologic, head and neck, rectum, and prostate cancers as well as eye plaques and electronic brachytherapy treatments were investigated by comparing dose calculations based on the TG-43 formalism and model-based dose calculation algorithms.
2017
Microdosimetry calculations for monoenergetic electrons using Geant4-DNA combined with a weighted track sampling algorithm Journal Article
In: Physics in Medicine and Biology, vol. 62, no. 13, pp. 5495–5508, 2017, ISSN: 1361-6560.
@article{famulari_microdosimetry_2017,
title = {Microdosimetry calculations for monoenergetic electrons using Geant4-DNA combined with a weighted track sampling algorithm},
author = {Gabriel Famulari and Piotr Pater and Shirin A. Enger},
doi = {10.1088/1361-6560/aa71f6},
issn = {1361-6560},
year = {2017},
date = {2017-07-01},
journal = {Physics in Medicine and Biology},
volume = {62},
number = {13},
pages = {5495--5508},
abstract = {The aim of this study was to calculate microdosimetric distributions for low energy electrons simulated using the Monte Carlo track structure code Geant4-DNA. Tracks for monoenergetic electrons with kinetic energies ranging from 100 eV to 1 MeV were simulated in an infinite spherical water phantom using the Geant4-DNA extension included in Geant4 toolkit version 10.2 (patch 02). The microdosimetric distributions were obtained through random sampling of transfer points and overlaying scoring volumes within the associated volume of the tracks. Relative frequency distributions of energy deposition f(textgreaterE)/f(textgreater0) and dose mean lineal energy ([Formula: see text]) values were calculated in nanometer-sized spherical and cylindrical targets. The effects of scoring volume and scoring techniques were examined. The results were compared with published data generated using MOCA8B and KURBUC. Geant4-DNA produces a lower frequency of higher energy deposits than MOCA8B. The [Formula: see text] values calculated with Geant4-DNA are smaller than those calculated using MOCA8B and KURBUC. The differences are mainly due to the lower ionization and excitation cross sections of Geant4-DNA for low energy electrons. To a lesser extent, discrepancies can also be attributed to the implementation in this study of a new and fast scoring technique that differs from that used in previous studies. For the same mean chord length ([Formula: see text]), the [Formula: see text] calculated in cylindrical volumes are larger than those calculated in spherical volumes. The discrepancies due to cross sections and scoring geometries increase with decreasing scoring site dimensions. A new set of [Formula: see text] values has been presented for monoenergetic electrons using a fast track sampling algorithm and the most recent physics models implemented in Geant4-DNA. This dataset can be combined with primary electron spectra to predict the radiation quality of photon and electron beams.},
keywords = {Algorithms, DNA, DNA Damage, Electrons, Imaging, Monte Carlo Method, Phantoms, Photons, Radiometry},
pubstate = {published},
tppubtype = {article}
}
The aim of this study was to calculate microdosimetric distributions for low energy electrons simulated using the Monte Carlo track structure code Geant4-DNA. Tracks for monoenergetic electrons with kinetic energies ranging from 100 eV to 1 MeV were simulated in an infinite spherical water phantom using the Geant4-DNA extension included in Geant4 toolkit version 10.2 (patch 02). The microdosimetric distributions were obtained through random sampling of transfer points and overlaying scoring volumes within the associated volume of the tracks. Relative frequency distributions of energy deposition f(textgreaterE)/f(textgreater0) and dose mean lineal energy ([Formula: see text]) values were calculated in nanometer-sized spherical and cylindrical targets. The effects of scoring volume and scoring techniques were examined. The results were compared with published data generated using MOCA8B and KURBUC. Geant4-DNA produces a lower frequency of higher energy deposits than MOCA8B. The [Formula: see text] values calculated with Geant4-DNA are smaller than those calculated using MOCA8B and KURBUC. The differences are mainly due to the lower ionization and excitation cross sections of Geant4-DNA for low energy electrons. To a lesser extent, discrepancies can also be attributed to the implementation in this study of a new and fast scoring technique that differs from that used in previous studies. For the same mean chord length ([Formula: see text]), the [Formula: see text] calculated in cylindrical volumes are larger than those calculated in spherical volumes. The discrepancies due to cross sections and scoring geometries increase with decreasing scoring site dimensions. A new set of [Formula: see text] values has been presented for monoenergetic electrons using a fast track sampling algorithm and the most recent physics models implemented in Geant4-DNA. This dataset can be combined with primary electron spectra to predict the radiation quality of photon and electron beams.
2016
A brachytherapy photon radiation quality index Q(BT) for probe-type dosimetry Journal Article
In: Physica medica: PM: an international journal devoted to the applications of physics to medicine and biology: official journal of the Italian Association of Biomedical Physics (AIFB), vol. 32, no. 6, pp. 741–748, 2016, ISSN: 1724-191X.
@article{quast_brachytherapy_2016,
title = {A brachytherapy photon radiation quality index Q(BT) for probe-type dosimetry},
author = {Ulrich Quast and Theodor W. Kaulich and José T. Álvarez-Romero and Sa Carlsson Tedgren and Shirin A. Enger and David C. Medich and Firas Mourtada and Jose Perez-Calatayud and Mark J. Rivard and G. Abu Zakaria},
doi = {10.1016/j.ejmp.2016.03.008},
issn = {1724-191X},
year = {2016},
date = {2016-06-01},
journal = {Physica medica: PM: an international journal devoted to the applications of physics to medicine and biology: official journal of the Italian Association of Biomedical Physics (AIFB)},
volume = {32},
number = {6},
pages = {741--748},
abstract = {INTRODUCTION: In photon brachytherapy (BT), experimental dosimetry is needed to verify treatment plans if planning algorithms neglect varying attenuation, absorption or scattering conditions. The detector's response is energy dependent, including the detector material to water dose ratio and the intrinsic mechanisms. The local mean photon energy E¯(r) must be known or another equivalent energy quality parameter used. We propose the brachytherapy photon radiation quality indexQ(BT)(E¯), to characterize the photon radiation quality in view of measurements of distributions of the absorbed dose to water, Dw, around BT sources. MATERIALS AND METHODS: While the external photon beam radiotherapy (EBRT) radiation quality index Q(EBRT)(E¯)=TPR10(20)(E¯) is not applicable to BT, the authors have applied a novel energy dependent parameter, called brachytherapy photon radiation quality index, defined as Q(BT)(E¯)=Dprim(r=2cm,θ0=90°)/Dprim(r0=1cm,θ0=90°), utilizing precise primary absorbed dose data, Dprim, from source reference databases, without additional MC-calculations. RESULTS AND DISCUSSION: For BT photon sources used clinically, Q(BT)(E¯) enables to determine the effective mean linear attenuation coefficient μ¯(E) and thus the effective energy of the primary photons Eprim(eff)(r0,θ0) at the TG-43 reference position Pref(r0=1cm,θ0=90°), being close to the mean total photon energy E¯tot(r0,θ0). If one has calibrated detectors, published E¯tot(r) and the BT radiation quality correction factor [Formula: see text] for different BT radiation qualities Q and Q0, the detector's response can be determined and Dw(r,θ) measured in the vicinity of BT photon sources.
CONCLUSIONS: This novel brachytherapy photon radiation quality indexQ(BT) characterizes sufficiently accurate and precise the primary photon's penetration probability and scattering potential.},
keywords = {Absorbed dose to water, Brachytherapy, Detector response, Effective energy, Photon brachytherapy radiation quality index, Photons, Radiation, Radiometry, Scattering, Uncertainty},
pubstate = {published},
tppubtype = {article}
}
INTRODUCTION: In photon brachytherapy (BT), experimental dosimetry is needed to verify treatment plans if planning algorithms neglect varying attenuation, absorption or scattering conditions. The detector’s response is energy dependent, including the detector material to water dose ratio and the intrinsic mechanisms. The local mean photon energy E¯(r) must be known or another equivalent energy quality parameter used. We propose the brachytherapy photon radiation quality indexQ(BT)(E¯), to characterize the photon radiation quality in view of measurements of distributions of the absorbed dose to water, Dw, around BT sources. MATERIALS AND METHODS: While the external photon beam radiotherapy (EBRT) radiation quality index Q(EBRT)(E¯)=TPR10(20)(E¯) is not applicable to BT, the authors have applied a novel energy dependent parameter, called brachytherapy photon radiation quality index, defined as Q(BT)(E¯)=Dprim(r=2cm,θ0=90°)/Dprim(r0=1cm,θ0=90°), utilizing precise primary absorbed dose data, Dprim, from source reference databases, without additional MC-calculations. RESULTS AND DISCUSSION: For BT photon sources used clinically, Q(BT)(E¯) enables to determine the effective mean linear attenuation coefficient μ¯(E) and thus the effective energy of the primary photons Eprim(eff)(r0,θ0) at the TG-43 reference position Pref(r0=1cm,θ0=90°), being close to the mean total photon energy E¯tot(r0,θ0). If one has calibrated detectors, published E¯tot(r) and the BT radiation quality correction factor [Formula: see text] for different BT radiation qualities Q and Q0, the detector’s response can be determined and Dw(r,θ) measured in the vicinity of BT photon sources.
CONCLUSIONS: This novel brachytherapy photon radiation quality indexQ(BT) characterizes sufficiently accurate and precise the primary photon’s penetration probability and scattering potential.
CONCLUSIONS: This novel brachytherapy photon radiation quality indexQ(BT) characterizes sufficiently accurate and precise the primary photon’s penetration probability and scattering potential.
2013
Gadolinium-153 as a brachytherapy isotope Journal Article
In: Physics in Medicine and Biology, vol. 58, no. 4, pp. 957–964, 2013, ISSN: 1361-6560.
@article{enger_gadolinium-153_2013,
title = {Gadolinium-153 as a brachytherapy isotope},
author = {Shirin A. Enger and Darrell R. Fisher and Ryan T. Flynn},
doi = {10.1088/0031-9155/58/4/957},
issn = {1361-6560},
year = {2013},
date = {2013-02-01},
journal = {Physics in Medicine and Biology},
volume = {58},
number = {4},
pages = {957--964},
abstract = {The purpose of this work was to present the fundamental dosimetric characteristics of a hypothetical (153)Gd brachytherapy source using the AAPM TG-43U1 dose-calculation formalism. Gadolinium-153 is an intermediate-energy isotope that emits 40-100 keV photons with a half-life of 242 days. The rationale for considering (153)Gd as a brachytherapy source is for its potential of patient specific shielding and to enable reduced personnel shielding requirements relative to (192)Ir, and as an isotope for interstitial rotating shield brachytherapy (I-RSBT). A hypothetical (153)Gd brachytherapy source with an active core of 0.84 mm diameter, 10 mm length and specific activity of 5.55 TBq of (153)Gd per gram of Gd was simulated with Geant4. The encapsulation material was stainless steel with a thickness of 0.08 mm. The radial dose function, anisotropy function and photon spectrum in water were calculated for the (153)Gd source. The simulated (153)Gd source had an activity of 242 GBq and a dose rate in water 1 cm off axis of 13.12 Gy h(-1), indicating that it would be suitable as a low-dose-rate or pulsed-dose-rate brachytherapy source. The beta particles emitted have low enough energies to be absorbed in the source encapsulation. Gadolinium-153 has an increasing radial dose function due to multiple scatter of low-energy photons. Scattered photon dose takes over with distance from the source and contributes to the majority of the absorbed dose. The anisotropy function of the (153)Gd source decreases at low polar angles, as a result of the long active core. The source is less anisotropic at polar angles away from the longitudinal axes. The anisotropy function increases with increasing distance. The (153)Gd source considered would be suitable as an intermediate-energy low-dose-rate or pulsed-dose-rate brachytherapy source. The source could provide a means for I-RSBT delivery and enable brachytherapy treatments with patient specific shielding and reduced personnel shielding requirements relative to (192)Ir.},
keywords = {Anisotropy, Brachytherapy, Equipment Design, Gadolinium, Humans, Iridium Radioisotopes, Male, Monte Carlo Method, Photons, Prostatic Neoplasms, Radiation, Radiation Protection, Radioisotopes, Radiotherapy Dosage, Scattering},
pubstate = {published},
tppubtype = {article}
}
The purpose of this work was to present the fundamental dosimetric characteristics of a hypothetical (153)Gd brachytherapy source using the AAPM TG-43U1 dose-calculation formalism. Gadolinium-153 is an intermediate-energy isotope that emits 40-100 keV photons with a half-life of 242 days. The rationale for considering (153)Gd as a brachytherapy source is for its potential of patient specific shielding and to enable reduced personnel shielding requirements relative to (192)Ir, and as an isotope for interstitial rotating shield brachytherapy (I-RSBT). A hypothetical (153)Gd brachytherapy source with an active core of 0.84 mm diameter, 10 mm length and specific activity of 5.55 TBq of (153)Gd per gram of Gd was simulated with Geant4. The encapsulation material was stainless steel with a thickness of 0.08 mm. The radial dose function, anisotropy function and photon spectrum in water were calculated for the (153)Gd source. The simulated (153)Gd source had an activity of 242 GBq and a dose rate in water 1 cm off axis of 13.12 Gy h(-1), indicating that it would be suitable as a low-dose-rate or pulsed-dose-rate brachytherapy source. The beta particles emitted have low enough energies to be absorbed in the source encapsulation. Gadolinium-153 has an increasing radial dose function due to multiple scatter of low-energy photons. Scattered photon dose takes over with distance from the source and contributes to the majority of the absorbed dose. The anisotropy function of the (153)Gd source decreases at low polar angles, as a result of the long active core. The source is less anisotropic at polar angles away from the longitudinal axes. The anisotropy function increases with increasing distance. The (153)Gd source considered would be suitable as an intermediate-energy low-dose-rate or pulsed-dose-rate brachytherapy source. The source could provide a means for I-RSBT delivery and enable brachytherapy treatments with patient specific shielding and reduced personnel shielding requirements relative to (192)Ir.
2012
Dose to tissue medium or water cavities as surrogate for the dose to cell nuclei at brachytherapy photon energies Journal Article
In: Physics in Medicine and Biology, vol. 57, no. 14, pp. 4489–4500, 2012, ISSN: 1361-6560.
@article{enger_dose_2012,
title = {Dose to tissue medium or water cavities as surrogate for the dose to cell nuclei at brachytherapy photon energies},
author = {Shirin A. Enger and Anders Ahnesjö and Frank Verhaegen and Luc Beaulieu},
doi = {10.1088/0031-9155/57/14/4489},
issn = {1361-6560},
year = {2012},
date = {2012-07-01},
journal = {Physics in Medicine and Biology},
volume = {57},
number = {14},
pages = {4489--4500},
abstract = {It has been suggested that modern dose calculation algorithms should be able to report absorbed dose both as dose to the local medium, D(m,m,) and as dose to a water cavity embedded in the medium, D(w,m), using conversion factors from cavity theory. Assuming that the cell nucleus with its DNA content is the most important target for biological response, the aim of this study is to investigate, by means of Monte Carlo (MC) simulations, the relationship of the dose to a cell nucleus in a medium, D(n,m,) to D(m,m) and D(w,m), for different combinations of cell nucleus compositions and tissue media for different photon energies used in brachytherapy. As D(n,m) is very impractical to calculate directly for routine treatment planning, while D(m,m) and D(w,m) are much easier to obtain, the questions arise which one of these quantities is the best surrogate for D(n,m) and which cavity theory assumptions should one use for its estimate. The Geant4.9.4 MC code was used to calculate D(m,m,) D(w,m) and D(n,m) for photon energies from 20 (representing the lower energy end of brachytherapy for ¹⁰³Pd or ¹²⁵I) to 300 keV (close to the mean energy of (¹⁹²Ir) and for the tissue media adipose, breast, prostate and muscle. To simulate the cell and its nucleus, concentric spherical cavities were placed inside a cubic phantom (10 × 10 × 10 mm³). The diameter of the simulated nuclei was set to 14 µm. For each tissue medium, three different setups were simulated; (a) D(n,m) was calculated with nuclei embedded in tissues (MC-D(n,m)). Four different published elemental compositions of cell nuclei were used. (b) D(w,m) was calculated with MC (MC-D(w,m)) and compared with large cavity theory calculated D(w,m) (LCT-D(w,m)), and small cavity theory calculated D(w,m) (SCT-D(w,m)). (c) D(m,m) was calculated with MC (MC-D(m,m)). MC-D(w,m) is a good substitute for MC-D(n,m) for all photon energies and for all simulated nucleus compositions and tissue types. SCT-D(w,m) can be used for most energies in brachytherapy, while LCT-D(w,m) should only be considered for source spectra well below 50 keV, since contributions to the absorbed dose inside the nucleus to a large degree stem from electrons released in the surrounding medium. MC-D(m,m) is not an appropriate substitute for MC-D(n,m) for the lowest photon energies for adipose and breast tissues. The ratio of MC-D(m,m) to MC-D(n,m) for adipose and breast tissue deviates from unity by 34% and 15% respectively for the lowest photon energy (20 keV), whereas the ratio is close to unity for higher energies. For prostate and muscle tissue MC-D(m,m) is a good substitute for MC-D(n,m). However, for all photon energies and tissue types the nucleus composition with the highest hydrogen content behaves differently than other compositions. Elemental compositions of the tissue and nuclei affect considerably the absorbed dose to the cell nuclei for brachytherapy sources, in particular those at the low-energy end of the spectrum. Thus, there is a need for more accurate data for the elemental compositions of tumours and healthy cells. For the nucleus compositions and tissue types investigated, MC-D(w,m) is a good substitute to MC-D(n,m) for all simulated photon energies. Whether other studied surrogates are good approximations to MC-D(n,m) depends on the target size, target composition, composition of the surrounding tissue and photon energy.},
keywords = {Brachytherapy, Cell Line, Cell Nucleus, Humans, Monte Carlo Method, Photons, Radiation Dosage, Radiotherapy Dosage, Water},
pubstate = {published},
tppubtype = {article}
}
It has been suggested that modern dose calculation algorithms should be able to report absorbed dose both as dose to the local medium, D(m,m,) and as dose to a water cavity embedded in the medium, D(w,m), using conversion factors from cavity theory. Assuming that the cell nucleus with its DNA content is the most important target for biological response, the aim of this study is to investigate, by means of Monte Carlo (MC) simulations, the relationship of the dose to a cell nucleus in a medium, D(n,m,) to D(m,m) and D(w,m), for different combinations of cell nucleus compositions and tissue media for different photon energies used in brachytherapy. As D(n,m) is very impractical to calculate directly for routine treatment planning, while D(m,m) and D(w,m) are much easier to obtain, the questions arise which one of these quantities is the best surrogate for D(n,m) and which cavity theory assumptions should one use for its estimate. The Geant4.9.4 MC code was used to calculate D(m,m,) D(w,m) and D(n,m) for photon energies from 20 (representing the lower energy end of brachytherapy for ¹⁰³Pd or ¹²⁵I) to 300 keV (close to the mean energy of (¹⁹²Ir) and for the tissue media adipose, breast, prostate and muscle. To simulate the cell and its nucleus, concentric spherical cavities were placed inside a cubic phantom (10 × 10 × 10 mm³). The diameter of the simulated nuclei was set to 14 µm. For each tissue medium, three different setups were simulated; (a) D(n,m) was calculated with nuclei embedded in tissues (MC-D(n,m)). Four different published elemental compositions of cell nuclei were used. (b) D(w,m) was calculated with MC (MC-D(w,m)) and compared with large cavity theory calculated D(w,m) (LCT-D(w,m)), and small cavity theory calculated D(w,m) (SCT-D(w,m)). (c) D(m,m) was calculated with MC (MC-D(m,m)). MC-D(w,m) is a good substitute for MC-D(n,m) for all photon energies and for all simulated nucleus compositions and tissue types. SCT-D(w,m) can be used for most energies in brachytherapy, while LCT-D(w,m) should only be considered for source spectra well below 50 keV, since contributions to the absorbed dose inside the nucleus to a large degree stem from electrons released in the surrounding medium. MC-D(m,m) is not an appropriate substitute for MC-D(n,m) for the lowest photon energies for adipose and breast tissues. The ratio of MC-D(m,m) to MC-D(n,m) for adipose and breast tissue deviates from unity by 34% and 15% respectively for the lowest photon energy (20 keV), whereas the ratio is close to unity for higher energies. For prostate and muscle tissue MC-D(m,m) is a good substitute for MC-D(n,m). However, for all photon energies and tissue types the nucleus composition with the highest hydrogen content behaves differently than other compositions. Elemental compositions of the tissue and nuclei affect considerably the absorbed dose to the cell nuclei for brachytherapy sources, in particular those at the low-energy end of the spectrum. Thus, there is a need for more accurate data for the elemental compositions of tumours and healthy cells. For the nucleus compositions and tissue types investigated, MC-D(w,m) is a good substitute to MC-D(n,m) for all simulated photon energies. Whether other studied surrogates are good approximations to MC-D(n,m) depends on the target size, target composition, composition of the surrounding tissue and photon energy.
2011
Modeling a hypothetical 170Tm source for brachytherapy applications Journal Article
In: Medical Physics, vol. 38, no. 10, pp. 5307–5310, 2011, ISSN: 0094-2405.
@article{enger_modeling_2011,
title = {Modeling a hypothetical 170Tm source for brachytherapy applications},
author = {Shirin A. Enger and Michel D'Amours and Luc Beaulieu},
doi = {10.1118/1.3626482},
issn = {0094-2405},
year = {2011},
date = {2011-10-01},
journal = {Medical Physics},
volume = {38},
number = {10},
pages = {5307--5310},
abstract = {PURPOSE: To perform absorbed dose calculations based on Monte Carlo simulations for a hypothetical (170)Tm source and to investigate the influence of encapsulating material on the energy spectrum of the emitted electrons and photons.
METHODS: GEANT4 Monte Carlo code version 9.2 patch 2 was used to simulate the decay process of (170)Tm and to calculate the absorbed dose distribution using the GEANT4 Penelope physics models. A hypothetical (170)Tm source based on the Flexisource brachytherapy design with the active core set as a pure thulium cylinder (length 3.5 mm and diameter 0.6 mm) and different cylindrical source encapsulations (length 5 mm and thickness 0.125 mm) constructed of titanium, stainless-steel, gold, or platinum were simulated. The radial dose function for the line source approximation was calculated following the TG-43U1 formalism for the stainless-steel encapsulation.
RESULTS: For the titanium and stainless-steel encapsulation, 94% of the total bremsstrahlung is produced inside the core, 4.8 and 5.5% in titanium and stainless-steel capsules, respectively, and less than 1% in water. For the gold capsule, 85% is produced inside the core, 14.2% inside the gold capsule, and a negligible amount (textless1%) in water. Platinum encapsulation resulted in bremsstrahlung effects similar to those with the gold encapsulation. The range of the beta particles decreases by 1.1 mm with the stainless-steel encapsulation compared to the bare source but the tissue will still receive dose from the beta particles several millimeters from the source capsule. The gold and platinum capsules not only absorb most of the electrons but also attenuate low energy photons. The mean energy of the photons escaping the core and the stainless-steel capsule is 113 keV while for the gold and platinum the mean energy is 160 keV and 165 keV, respectively.
CONCLUSIONS: A (170)Tm source is primarily a bremsstrahlung source, with the majority of bremsstrahlung photons being generated in the source core and experiencing little attenuation in the source encapsulation. Electrons are efficiently absorbed by the gold and platinum encapsulations. However, for the stainless-steel capsule (or other lower Z encapsulations) electrons will escape. The dose from these electrons is dominant over the photon dose in the first few millimeter but is not taken into account by current standard treatment planning systems. The total energy spectrum of photons emerging from the source depends on the encapsulation composition and results in mean photon energies well above 100 keV. This is higher than the main gamma-ray energy peak at 84 keV. Based on our results, the use of (170)Tm as a brachytherapy source presents notable challenges.},
keywords = {Algorithms, Brachytherapy, Computer Simulation, Computer-Assisted, Electrons, Equipment Design, Gold, Humans, Models, Monte Carlo Method, Photons, Platinum, Radioisotopes, Radiotherapy Planning, Stainless Steel, Theoretical, Thulium, Titanium},
pubstate = {published},
tppubtype = {article}
}
PURPOSE: To perform absorbed dose calculations based on Monte Carlo simulations for a hypothetical (170)Tm source and to investigate the influence of encapsulating material on the energy spectrum of the emitted electrons and photons.
METHODS: GEANT4 Monte Carlo code version 9.2 patch 2 was used to simulate the decay process of (170)Tm and to calculate the absorbed dose distribution using the GEANT4 Penelope physics models. A hypothetical (170)Tm source based on the Flexisource brachytherapy design with the active core set as a pure thulium cylinder (length 3.5 mm and diameter 0.6 mm) and different cylindrical source encapsulations (length 5 mm and thickness 0.125 mm) constructed of titanium, stainless-steel, gold, or platinum were simulated. The radial dose function for the line source approximation was calculated following the TG-43U1 formalism for the stainless-steel encapsulation.
RESULTS: For the titanium and stainless-steel encapsulation, 94% of the total bremsstrahlung is produced inside the core, 4.8 and 5.5% in titanium and stainless-steel capsules, respectively, and less than 1% in water. For the gold capsule, 85% is produced inside the core, 14.2% inside the gold capsule, and a negligible amount (textless1%) in water. Platinum encapsulation resulted in bremsstrahlung effects similar to those with the gold encapsulation. The range of the beta particles decreases by 1.1 mm with the stainless-steel encapsulation compared to the bare source but the tissue will still receive dose from the beta particles several millimeters from the source capsule. The gold and platinum capsules not only absorb most of the electrons but also attenuate low energy photons. The mean energy of the photons escaping the core and the stainless-steel capsule is 113 keV while for the gold and platinum the mean energy is 160 keV and 165 keV, respectively.
CONCLUSIONS: A (170)Tm source is primarily a bremsstrahlung source, with the majority of bremsstrahlung photons being generated in the source core and experiencing little attenuation in the source encapsulation. Electrons are efficiently absorbed by the gold and platinum encapsulations. However, for the stainless-steel capsule (or other lower Z encapsulations) electrons will escape. The dose from these electrons is dominant over the photon dose in the first few millimeter but is not taken into account by current standard treatment planning systems. The total energy spectrum of photons emerging from the source depends on the encapsulation composition and results in mean photon energies well above 100 keV. This is higher than the main gamma-ray energy peak at 84 keV. Based on our results, the use of (170)Tm as a brachytherapy source presents notable challenges.
METHODS: GEANT4 Monte Carlo code version 9.2 patch 2 was used to simulate the decay process of (170)Tm and to calculate the absorbed dose distribution using the GEANT4 Penelope physics models. A hypothetical (170)Tm source based on the Flexisource brachytherapy design with the active core set as a pure thulium cylinder (length 3.5 mm and diameter 0.6 mm) and different cylindrical source encapsulations (length 5 mm and thickness 0.125 mm) constructed of titanium, stainless-steel, gold, or platinum were simulated. The radial dose function for the line source approximation was calculated following the TG-43U1 formalism for the stainless-steel encapsulation.
RESULTS: For the titanium and stainless-steel encapsulation, 94% of the total bremsstrahlung is produced inside the core, 4.8 and 5.5% in titanium and stainless-steel capsules, respectively, and less than 1% in water. For the gold capsule, 85% is produced inside the core, 14.2% inside the gold capsule, and a negligible amount (textless1%) in water. Platinum encapsulation resulted in bremsstrahlung effects similar to those with the gold encapsulation. The range of the beta particles decreases by 1.1 mm with the stainless-steel encapsulation compared to the bare source but the tissue will still receive dose from the beta particles several millimeters from the source capsule. The gold and platinum capsules not only absorb most of the electrons but also attenuate low energy photons. The mean energy of the photons escaping the core and the stainless-steel capsule is 113 keV while for the gold and platinum the mean energy is 160 keV and 165 keV, respectively.
CONCLUSIONS: A (170)Tm source is primarily a bremsstrahlung source, with the majority of bremsstrahlung photons being generated in the source core and experiencing little attenuation in the source encapsulation. Electrons are efficiently absorbed by the gold and platinum encapsulations. However, for the stainless-steel capsule (or other lower Z encapsulations) electrons will escape. The dose from these electrons is dominant over the photon dose in the first few millimeter but is not taken into account by current standard treatment planning systems. The total energy spectrum of photons emerging from the source depends on the encapsulation composition and results in mean photon energies well above 100 keV. This is higher than the main gamma-ray energy peak at 84 keV. Based on our results, the use of (170)Tm as a brachytherapy source presents notable challenges.