Mission
Members
Projects
Intensity Modulated Brachytherapy
Alana Thibodeau-Antonacci, Ph.D. Student, Jake Reid, M.Sc. Student, Maude Robitaille, M.Sc. Student, & Bjorn Moren, Postdoctoral Fellow
The critical limitation with brachytherapy is the rotationally symmetric dose distribution provided by brachytherapy sources, delivering high dose to the tumor but often with poor tumor conformity due to the non-symmetrical shape of the tumors resulting in dose spillage to surrounding healthy tissues.
For example, large and irregular gynecological tumors, which extend into the parametrial and/or paravaginal tissues cannot be treated with curative intend by using intracavitary brachytherapy implants alone without overdosing nearby healthy organs causing side effects but must be supplemented with invasive interstitial high dose rate brachytherapy to enable conformal dose delivery to the tumor while reducing dose to healthy tissues. However, despite the excellent clinical results, this treatment is not available to all patients due to its invasive nature, lack of resources and trained radiation oncologists. For prostate cancer, disease-free survival is higher in patients treated with high dose rate brachytherapy combined with external beam radiotherapy compared to those treated with external beam radiotherapy alone.
Our group is developing the next generation of high dose rate brachytherapy technology, including prototype delivery systems for intensity modulated brachytherapy treatment of prostate, cervix, vaginal and rectal cancers. These systems will enable anisotropic intensity modulation of brachytherapy dose distributions by incorporating rotating metallic shields inside brachytherapy catheters and applicators.
Designed and delivered with accurate anatomic reference, the developed systems will tailor treatments to each individual patient by treating all parts of the tumor without needlessly irradiating large regions of normal tissues surrounding the tumor. Intensity modulated brachytherapy will increase the probability of response and cure while avoiding toxicity, which will increase the quality of life of patients suffering from cancer.
Monte Carlo-based Dosimetry
Jonathan Kalinowski, M.Sc. Student
Monte Carlo method is gold standard in simulation of radiation interaction with matter and is widely used in medical imaging and radiation physics. It plays a key role in medical physics research and development of novel technology for imaging and therapy equipment. Our group develops Monte Carlo based radiation dose calculation engines and treatment planning systems for use in conventional and intensity modulated brachytherapy, as well external beam radiotherapy.
For brachytherapy applications we have developed a Monte Carlo based radiation transport package called RapidBrachyMC, coupled to dose optimization algorithms, contouring tools and a comprehensive analysis package. This toolkit is standalone and enables planning of an optimal and accurate radiation dose to the tumour while sparing healthy tissues. The complete treatment planning system is called RapidBrachyMCTPS. It can be used to validate dose distributions from clinical treatment planning systems or commercial model-based dose calculation algorithms and is also well suited to develop and validate novel combinations of radiation sources and applicators, especially those shielded with high-Z materials.
Characterizing the Axxent® electronic brachytherapy source x-ray spectrum and its dosimetry
Azin Esmaelbeigi, Ph.D. Student
In addition to sealed photon emitting radionuclides, electronic x-ray systems can also be used to deliver high dose rate brachytherapy. At the Jewish General Hospital, we use the Axxent® electronic brachytherapy system (Xoft Inc., Fremont, California) to treat rectal cancer. This system uses a miniature electronic x-ray source (50 kVp) contained within a flexible probe to generate low energy x-rays. Azin is characterizing the Axxent® electronic brachytherapy source x-ray spectrum and its dosimetry through x-ray spectrometery, Monte Carlo simulations as well as measurements with ion chambers, scintillator based detectors and radiochromic films.
Development of a Fast and Accurate Dosimetry Toolkit for Radioembolization with Yttrium-90
Diane Alvarez, Ph.D. Student & Peter Kim, M.Sc.
The standard dosimetry for radionuclide-based cancer treatments is built on the simplistic medical internal radiation dose (MIRD) formalism that assumes a uniform radionuclide and absorbed dose distribution in the tumor. A more accurate dosimetry method that considers a heterogeneous radionuclide uptake and hence a heterogeneous dose distribution in the tumor is required. Ideally, attenuation of the radiation by heterogeneities in the patient tissues should also be taken into account. The purpose of this project is to develop and validate an image-based dosimetry software with a Monte Carlo dose calculation engine that will enable accurate and personalized dosimetry. The software considers heterogeneous radionuclide uptake and attenuation of the radiation by heterogeneities in the patient tissues.
Although the software toolkit may be applicable to many radionuclide treatments, this project focuses on a treatment called radioembolization, which uses Yttirum-90 filled resin or glass microspheres. Injected through a micro-catheter, microspheres are selectively deposited and permanently lodged within the hepatic arteries to preferentially irradiate hepatic tumors. With this software, we aim to establish a standard methodology that provides accurate dosimetry.
Treatment Plan Optimization in High Dose Rate Brachytherapy
Hossein Jafarzadeh, M.Sc. Student
Catheter Position Optimization in High Dose Rate Brachytherapy
In interstitial high dose rate brachytherapy, a highly radioactive source, usually 192Ir, is temporarily placed inside or in proximity of the tumor via thin hollow implanted catheters which are connected a machine called an afterloader. The afterloader contains a single radioactive source at the end of a wire. The source is pushed into each of the catheters, one by one under computer control and guided to the tumor site. The computer controls where along the catheter the source should pause to deliver its radiation (dwell positions) and how long it dwells at each position (dwell time). After the desired dose is delivered, the source is pulled back to the afterloader and the catheters are removed. Since the dwell times are optimized, the position of catheters has a major impact on the treatment plan quality. Efforts in optimizing the catheter positions have not been explored as extensively as the other aspects of the treatment planning workflow. This gap in knowledge motivates us to further explore this problem.
Penalty Weight Optimization in High Dose Rate Brachytherapy
Treatment plan optimization problem in high dose rate brachytherapy is formulated as a constrained optimization problem. First the dose constraints and penalty weights are determined by the clinicians, then the optimization problem is solved by linear programing. The dose constraints are usually fixed for each patient depending on the treated tumor site and the treatment planning guidelines followed. However, the clinicians select different penalty weights, leading to different optimization problems and finally adopt the one that results in the most desirable dose distribution. To remove the clinicians, influence on plan quality, reinforcement learning is explored.
Development of a Software Package for Monte Carlo-based Intravascular Brachytherapy Dosimetry
Maryam Rahbaran, M.Sc. Student
Intravascular brachytherapy is a means of treating restenosis after an angioplasty and stent insertion. Angioplasty and stent insertion can provoke an inflammatory response in the treated vessel which causes the rapid proliferation of neotintimal (scar) tissue. By eliminating neointimal tissue, intravascular brachytherapy allows treated vessels to maintain a healthy diameter. In recent years intravascular brachytherapy has seen reduced use, in favour of drug eluting stents. However, a demand for intravascular brachytherapy continues to exist in patients for whom drug eluting stents have been unsuccessful.
Beta sources are typically used in intravascular brachytherapy to reduce the need for radiation shielding in catheterization labs and to reduce the dose delivered to healthy tissues of the patient. Beta sources have high dose gradients that are affected by the presence of heterogeneities. Arterial plaques, stents, and guidewires have been shown to reduce the dose delivered to target volume from beta sources in intravascular brachytherapy. Our work allows for an understanding of the dosimetric shortcomings of commercially available intravascular brachytherapy delivery systems.
Publications
2018
Famulari, Gabriel; Enger, Shirin A.
Intensity modulated brachytherapy system for dynamic modulation of shielded catheters Presentation
Radiotherapy and Oncology, 01.04.2018, ISSN: 0167-8140, 1879-0887.
@misc{Famulari2018c,
title = {Intensity modulated brachytherapy system for dynamic modulation of shielded catheters},
author = {Gabriel Famulari and Shirin A. Enger},
url = {https://www.thegreenjournal.com/article/S0167-8140(18)30483-3/fulltext},
doi = {10.1016/S0167-8140(18)30483-3},
issn = {0167-8140, 1879-0887},
year = {2018},
date = {2018-04-01},
abstract = {www.thegreenjournal.com},
howpublished = {Radiotherapy and Oncology},
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Famulari, Gabriel; Pater, Piotr; Enger, Shirin A.
Microdosimetric Evaluation of Current and Alternative Brachytherapy Sources-A Geant4-DNA Simulation Study Journal Article
In: International Journal of Radiation Oncology, Biology, Physics, 100 (1), pp. 270–277, 2018, ISSN: 1879-355X.
@article{famulari_microdosimetric_2018,
title = {Microdosimetric Evaluation of Current and Alternative Brachytherapy Sources-A Geant4-DNA Simulation Study},
author = {Gabriel Famulari and Piotr Pater and Shirin A. Enger},
doi = {10.1016/j.ijrobp.2017.09.040},
issn = {1879-355X},
year = {2018},
date = {2018-01-01},
journal = {International Journal of Radiation Oncology, Biology, Physics},
volume = {100},
number = {1},
pages = {270--277},
abstract = {PURPOSE: Radioisotopes such as 75Se, 169Yb, and 153Gd have photon energy spectra and half-lives that make them excellent candidates as alternatives to 192Ir for high-dose-rate brachytherapy. The aim of the present study was to evaluate the relative biological effectiveness (RBE) of current (192Ir, 125I, 103Pd) and alternative (75Se, 169Yb, 153Gd) brachytherapy radionuclides using Monte Carlo simulations of lineal energy distributions.
METHODS AND MATERIALS: Brachytherapy sources (microSelectron v2 [192Ir, 75Se, 169Yb, 153Gd], SelectSeed [125I], and TheraSeed [103Pd]) were placed in the center of a spherical water phantom with a radius of 40 cm using the Geant4 Monte Carlo simulation toolkit. The kinetic energy of all primary, scattered, and fluorescence photons interacting in a scoring volume were tallied at various depths from the source. Electron tracks were generated by sampling the photon interaction spectrum and tracking all the interactions down to 10 eV using the event-by-event capabilities of the Geant4-DNA models. The dose mean lineal energy (y¯D) values were obtained through random sampling of transfer points and overlaying spherical scoring volumes within the associated volume of the tracks. The scoring volume diameter was determined by fitting the y¯D ratio for 125I to its observed RBE.
RESULTS: y¯D increased with the increasing distance from the source for 192Ir, 75Se, and 169Yb, remained constant for 153Gd and 125I, and decreased for 103Pd. The diameter at which the y¯D ratio coincided with the RBE of 1.15 to 1.20 for 125I was ∼25 to 40 nm. The RBE (reference 1 MeV photons) at high doses and dose rates for 192Ir, 75Se, 169Yb, 153Gd, 125I, and 103Pd was 1.028 to 1.034, 1.05 to 1.07, 1.12 to 1.15, 1.16 to 1.21, 1.15 to 1.20, and 1.17 to 1.22, respectively.
CONCLUSIONS: The radiation quality of the radionuclides under investigation was greater than that of high-energy photons. The present study has provided a set of values to modify the prescription doses for brachytherapy to account for the variation in radiation quality among radionuclides.},
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pubstate = {published},
tppubtype = {article}
}
METHODS AND MATERIALS: Brachytherapy sources (microSelectron v2 [192Ir, 75Se, 169Yb, 153Gd], SelectSeed [125I], and TheraSeed [103Pd]) were placed in the center of a spherical water phantom with a radius of 40 cm using the Geant4 Monte Carlo simulation toolkit. The kinetic energy of all primary, scattered, and fluorescence photons interacting in a scoring volume were tallied at various depths from the source. Electron tracks were generated by sampling the photon interaction spectrum and tracking all the interactions down to 10 eV using the event-by-event capabilities of the Geant4-DNA models. The dose mean lineal energy (y¯D) values were obtained through random sampling of transfer points and overlaying spherical scoring volumes within the associated volume of the tracks. The scoring volume diameter was determined by fitting the y¯D ratio for 125I to its observed RBE.
RESULTS: y¯D increased with the increasing distance from the source for 192Ir, 75Se, and 169Yb, remained constant for 153Gd and 125I, and decreased for 103Pd. The diameter at which the y¯D ratio coincided with the RBE of 1.15 to 1.20 for 125I was ∼25 to 40 nm. The RBE (reference 1 MeV photons) at high doses and dose rates for 192Ir, 75Se, 169Yb, 153Gd, 125I, and 103Pd was 1.028 to 1.034, 1.05 to 1.07, 1.12 to 1.15, 1.16 to 1.21, 1.15 to 1.20, and 1.17 to 1.22, respectively.
CONCLUSIONS: The radiation quality of the radionuclides under investigation was greater than that of high-energy photons. The present study has provided a set of values to modify the prescription doses for brachytherapy to account for the variation in radiation quality among radionuclides.
Famulari, Gabriel; Rayes, Roni F.; Enger, Shirin A.
AIM-Brachy - 5 finalists out of 42 projects in McGill Clinical Innovation Competition and Hakim Family Prize. Miscellaneous
AIMBrachy, 2018.
@misc{Famulari2018,
title = {AIM-Brachy - 5 finalists out of 42 projects in McGill Clinical Innovation Competition and Hakim Family Prize.},
author = {Gabriel Famulari and Roni F. Rayes and Shirin A. Enger},
year = {2018},
date = {2018-01-01},
howpublished = {AIMBrachy},
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Famulari, Gabriel; Enger, Shirin A.
Top 5 abstract at the ESTRO annual meeting Miscellaneous
ESTRO Annual meeting, 2018.
@misc{Famulari2018b,
title = {Top 5 abstract at the ESTRO annual meeting},
author = {Gabriel Famulari and Shirin A. Enger},
year = {2018},
date = {2018-01-01},
abstract = {Intensity-modulated brachytherapy system for dynamic modulation of shielded catheters, ESTRO Annual meeting. Barcelona, Spain. Selected as one of the five abstracts out of the numerous submitted at the ESTRO conference to highlight the type of innovative science presented in an area and published in the conference report. },
howpublished = {ESTRO Annual meeting},
keywords = {},
pubstate = {published},
tppubtype = {misc}
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2017
Famulari, Gabriel; Urlich, Tomas; Armstrong, Andrea; Enger, Shirin A.
Practical aspects of 153Gd as a radioactive source for use in brachytherapy Journal Article
In: Applied Radiation and Isotopes: Including Data, Instrumentation and Methods for Use in Agriculture, Industry and Medicine, 130 , pp. 131–139, 2017, ISSN: 1872-9800.
@article{famulari_practical_2017,
title = {Practical aspects of 153Gd as a radioactive source for use in brachytherapy},
author = {Gabriel Famulari and Tomas Urlich and Andrea Armstrong and Shirin A. Enger},
doi = {10.1016/j.apradiso.2017.09.028},
issn = {1872-9800},
year = {2017},
date = {2017-12-01},
journal = {Applied Radiation and Isotopes: Including Data, Instrumentation and Methods for Use in Agriculture, Industry and Medicine},
volume = {130},
pages = {131--139},
abstract = {The goal of this study was to investigate the production, purification and immobilization techniques for a 153Gd brachytherapy source. We have investigated the maximum attainable specific activity of 153Gd through the irradiation of Gd2O3 enriched to 30.6% 152Gd at McMaster Nuclear Reactor. The advantage of producing 153Gd through this production pathway is the possibility to irradiate pre-sealed pellets of 152Gd enriched Gd2O3, thereby removing the need to perform chemical separation with large quantities of radio-impurities. However, small amounts of long-lived impurities are produced from the irradiation of enriched 152Gd targets due to traces of Eu in the sample. If the amount of impurities produced is deemed unacceptable, 153Gd can be isolated as an aqueous solution, chemically separated from impurities and loaded onto a sorbent with a high affinity for Gd before encapsulation.},
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Famulari, Gabriel; Pater, Piotr; Enger, Shirin A.
Microdosimetry calculations for monoenergetic electrons using Geant4-DNA combined with a weighted track sampling algorithm Journal Article
In: Physics in Medicine and Biology, 62 (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.},
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Famulari, Gabriel; Renaud, Marc-André; Enger, Shirin A.
Top ranking submission to the Young Investigator Symposium Presentation
COMP Annual meeting, Young Investigator Symposium, 01.01.2017.
@misc{nokey,
title = {Top ranking submission to the Young Investigator Symposium},
author = {Gabriel Famulari and Marc-André Renaud and Shirin A. Enger},
year = {2017},
date = {2017-01-01},
urldate = {2017-01-01},
abstract = {An intensity-modulated delivery system for prostate brachytherapy using intermediate energy sources. This abstract was selected as one of the best abstracts to compete in the young investigator symposium.},
howpublished = {COMP Annual meeting, Young Investigator Symposium},
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Famulari, Gabriel; Pater, Piotr; Enger, Shirin A.
Microdosimetric evaluation of intermediate-energy brachytherapy sources using Geant4-DNA Presentation
Radiotherapy and Oncology, 01.01.2017.
@misc{Famulari2017,
title = {Microdosimetric evaluation of intermediate-energy brachytherapy sources using Geant4-DNA},
author = {Gabriel Famulari and Piotr Pater and Shirin A. Enger},
year = {2017},
date = {2017-01-01},
howpublished = {Radiotherapy and Oncology},
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Famulari, Gabriel; Renaud, Marc-André; Enger, Shirin A.
An intensity modulated delivery system for prostate brachytherapy using intermediate energy sources Presentation
Medical Physics, 01.01.2017.
@misc{Famulari2017b,
title = {An intensity modulated delivery system for prostate brachytherapy using intermediate energy sources},
author = {Gabriel Famulari and Marc-André Renaud and Shirin A. Enger},
year = {2017},
date = {2017-01-01},
howpublished = {Medical Physics},
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Famulari, Gabriel; Enger, Shirin A.
A Novel Delivery System for High Dose Rate Intensity Modulated Brachytherapy with Intermediate Energy Brachytherapy Radiation Sources Such as 169Yb Presentation
Brachytherapy, 01.01.2017.
@misc{Famulari2017c,
title = {A Novel Delivery System for High Dose Rate Intensity Modulated Brachytherapy with Intermediate Energy Brachytherapy Radiation Sources Such as 169Yb},
author = {Gabriel Famulari and Shirin A. Enger},
year = {2017},
date = {2017-01-01},
howpublished = {Brachytherapy},
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2016
Renaud, Marc-André; Famulari, Gabriel; Seuntjens, Jan; Enger, Shirin A.
Column generation-based Monte Carlo treatment planning for rotating shield brachytherapy Presentation
Radiotherapy and Oncology, 01.01.2016.
@misc{Renaud2016,
title = {Column generation-based Monte Carlo treatment planning for rotating shield brachytherapy},
author = {Marc-André Renaud and Gabriel Famulari and Jan Seuntjens and Shirin A. Enger},
year = {2016},
date = {2016-01-01},
urldate = {2016-01-01},
howpublished = {Radiotherapy and Oncology},
keywords = {},
pubstate = {published},
tppubtype = {presentation}
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Famulari, Gabriel; Armstrong, Andrea; Enger, Shirin A.
Production of Gd-153 as a source isotope for use in rotating shield high dose rate brachytherapy Presentation
Radiotherapy and Oncology, 01.01.2016.
@misc{Famulari2016,
title = {Production of Gd-153 as a source isotope for use in rotating shield high dose rate brachytherapy},
author = {Gabriel Famulari and Andrea Armstrong and Shirin A. Enger},
year = {2016},
date = {2016-01-01},
howpublished = {Radiotherapy and Oncology},
keywords = {},
pubstate = {published},
tppubtype = {presentation}
}
2012
Enger, Shirin A.; Landry, Guillaume; D'Amours, Michel; Verhaegen, Frank; Beaulieu, Luc; Asai, Makoto; Perl, Joseph
Layered mass geometry: a novel technique to overlay seeds and applicators onto patient geometry in Geant4 brachytherapy simulations Journal Article
In: Physics in Medicine and Biology, 57 (19), pp. 6269–6277, 2012, ISSN: 1361-6560.
@article{enger_layered_2012,
title = {Layered mass geometry: a novel technique to overlay seeds and applicators onto patient geometry in Geant4 brachytherapy simulations},
author = {Shirin A. Enger and Guillaume Landry and Michel D'Amours and Frank Verhaegen and Luc Beaulieu and Makoto Asai and Joseph Perl},
doi = {10.1088/0031-9155/57/19/6269},
issn = {1361-6560},
year = {2012},
date = {2012-10-01},
journal = {Physics in Medicine and Biology},
volume = {57},
number = {19},
pages = {6269--6277},
abstract = {A problem faced by all Monte Carlo (MC) particle transport codes is how to handle overlapping geometries. The Geant4 MC toolkit allows the user to create parallel geometries within a single application. In Geant4 the standard mass-containing geometry is defined in a simulation volume called the World Volume. Separate parallel geometries can be defined in parallel worlds, that is, alternate three dimensional simulation volumes that share the same coordinate system with the World Volume for geometrical event biasing, scoring of radiation interactions, and/or the creation of hits in detailed readout structures. Until recently, only one of those worlds could contain mass so these parallel worlds provided no solution to simplify a complex geometric overlay issue in brachytherapy, namely the overlap of radiation sources and applicators with a CT based patient geometry. The standard method to handle seed and applicator overlay in MC requires removing CT voxels whose boundaries would intersect sources, placing the sources into the resulting void and then backfilling the remaining space of the void with a relevant material. The backfilling process may degrade the accuracy of patient representation, and the geometrical complexity of the technique precludes using fast and memory-efficient coding techniques that have been developed for regular voxel geometries. The patient must be represented by the less memory and CPU-efficient Geant4 voxel placement technique, G4PVPlacement, rather than the more efficient G4NestedParameterization (G4NestedParam). We introduce for the first time a Geant4 feature developed to solve this issue: Layered Mass Geometry (LMG) whereby both the standard (CT based patient geometry) and the parallel world (seeds and applicators) may now have mass. For any area where mass is present in the parallel world, the parallel mass is used. Elsewhere, the mass of the standard world is used. With LMG the user no longer needs to remove patient CT voxels that would include for example seeds. The patient representation can be a regular voxel grid, conducive to G4NestedParam, and the patient CT derived materials remain exact, avoiding the inaccuracy of the backfilling technique. Post-implant dosimetry for one patient with (125)I permanent seed implant was performed using Geant4 version 9.5.p01 using three different geometrical techniques. The first technique was the standard described above (G4PVPlacement). The second technique placed patient voxels as before, but placed seeds with LMG (G4PVPlacement+LMG). The third technique placed patient voxels through G4NestedParam and seeds through LMG (G4NestedParam+LMG). All the scenarios were calculated with 3 different image compression factors to manipulate the number of voxels. Additionally, the dosimetric impact of the backfilling technique was investigated for the case of calcifications in close proximity of sources. LMG eliminated the need for backfilling and simplified geometry description. Of the two LMG techniques, G4PVPlacement+LMG had no benefit to calculation time or memory use, actually increasing calculation time, but G4NestedParam+LMG reduced both calculation time and memory. The benefits of G4NestedParam+LMG over standard G4PVPlacement increased with increasing voxel numbers. For the case of calcifications in close proximity to sources, LMG not only increased efficiency but also yielded more accurate dose calculation than G4PVPlacement. G4NestedParam in combination with LMG present a new, efficient approach to simulate radiation sources that overlap patient geometry. Cases with brachytherapy applicators would constitute a direct extension of the method.},
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Enger, Shirin A.; Ahnesjö, Anders; Verhaegen, Frank; Beaulieu, Luc
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, 57 (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.},
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}
Enger, Shirin A.; Lundqvist, Hans; D'Amours, Michel; Beaulieu, Luc
Exploring (57)Co as a new isotope for brachytherapy applications Journal Article
In: Medical Physics, 39 (5), pp. 2342–2345, 2012, ISSN: 0094-2405.
@article{enger_exploring_2012,
title = {Exploring (57)Co as a new isotope for brachytherapy applications},
author = {Shirin A. Enger and Hans Lundqvist and Michel D'Amours and Luc Beaulieu},
doi = {10.1118/1.3700171},
issn = {0094-2405},
year = {2012},
date = {2012-05-01},
journal = {Medical Physics},
volume = {39},
number = {5},
pages = {2342--2345},
abstract = {PURPOSE: The characteristics of the radionuclide (57)Co make it interesting for use as a brachytherapy source. (57)Co combines a possible high specific activity with the emission of relatively low-energy photons and a half-life (272 days) suitable for regular source exchanges in an afterloader. (57)Co decays by electron capture to the stable (57)Fe with emission of 136 and 122 keV photons.
METHODS: A hypothetical (57)Co source based on the Flexisource brachytherapy encapsulation with the active core set as a pure cobalt cylinder (length 3.5 mm and diameter 0.6 mm) covered with a cylindrical stainless-steel capsule (length 5 mm and thickness 0.125 mm) was simulated using Geant4 Monte Carlo (MC) code version 9.4. The radial dose function, g(r), and anisotropy function F(r,θ), for the line source approximation were calculated following the TG-43U1 formalism. The results were compared to well-known (192)Ir and (125)I radionuclides, representing the higher and the lower energy end of brachytherapy, respectively.
RESULTS: The mean energy of photons in water, after passing through the core and the encapsulation material was 123 keV. This hypothetical (57)Co source has an increasing g(r) due to multiple scatter of low-energy photons, which results in a more uniform dose distribution than (192)Ir.
CONCLUSIONS: (57)Co has many advantages compared to (192)Ir due to its low-energy gamma emissions without any electron contamination. (57)Co has an increasing g(r) that results in a more uniform dose distribution than (192)Ir due to its multiple scattered photons. The anisotropy of the (57)Co source is comparable to that of (192)Ir. Furthermore, (57)Co has lower shielding requirements than (192)Ir.},
keywords = {},
pubstate = {published},
tppubtype = {article}
}
METHODS: A hypothetical (57)Co source based on the Flexisource brachytherapy encapsulation with the active core set as a pure cobalt cylinder (length 3.5 mm and diameter 0.6 mm) covered with a cylindrical stainless-steel capsule (length 5 mm and thickness 0.125 mm) was simulated using Geant4 Monte Carlo (MC) code version 9.4. The radial dose function, g(r), and anisotropy function F(r,θ), for the line source approximation were calculated following the TG-43U1 formalism. The results were compared to well-known (192)Ir and (125)I radionuclides, representing the higher and the lower energy end of brachytherapy, respectively.
RESULTS: The mean energy of photons in water, after passing through the core and the encapsulation material was 123 keV. This hypothetical (57)Co source has an increasing g(r) due to multiple scatter of low-energy photons, which results in a more uniform dose distribution than (192)Ir.
CONCLUSIONS: (57)Co has many advantages compared to (192)Ir due to its low-energy gamma emissions without any electron contamination. (57)Co has an increasing g(r) that results in a more uniform dose distribution than (192)Ir due to its multiple scattered photons. The anisotropy of the (57)Co source is comparable to that of (192)Ir. Furthermore, (57)Co has lower shielding requirements than (192)Ir.
2011
Enger, Shirin A.; D'Amours, Michel; Beaulieu, Luc
Modeling a hypothetical 170Tm source for brachytherapy applications Journal Article
In: Medical Physics, 38 (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 = {},
pubstate = {published},
tppubtype = {article}
}
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.
Xu, Chen; Verhaegen, Frank; Laurendeau, Denis; Enger, Shirin A.; Beaulieu, Luc
An algorithm for efficient metal artifact reductions in permanent seed Journal Article
In: Medical Physics, 38 (1), pp. 47–56, 2011, ISSN: 0094-2405.
@article{xu_algorithm_2011,
title = {An algorithm for efficient metal artifact reductions in permanent seed},
author = {Chen Xu and Frank Verhaegen and Denis Laurendeau and Shirin A. Enger and Luc Beaulieu},
doi = {10.1118/1.3519988},
issn = {0094-2405},
year = {2011},
date = {2011-01-01},
journal = {Medical Physics},
volume = {38},
number = {1},
pages = {47--56},
abstract = {PURPOSE: In permanent seed implants, 60 to more than 100 small metal capsules are inserted in the prostate, creating artifacts in x-ray computed tomography (CT) imaging. The goal of this work is to develop an automatic method for metal artifact reduction (MAR) from small objects such as brachytherapy seeds for clinical applications.
METHODS: The approach for MAR is based on the interpolation of missing projections by directly using raw helical CT data (sinogram). First, an initial image is reconstructed from the raw CT data. Then, the metal objects segmented from the reconstructed image are reprojected back into the sinogram space to produce a metal-only sinogram. The Steger method is used to determine precisely the position and edges of the seed traces in the raw CT data. By combining the use of Steger detection and reprojections, the missing projections are detected and replaced by interpolation of non-missing neighboring projections.
RESULTS: In both phantom experiments and patient studies, the missing projections have been detected successfully and the artifacts caused by metallic objects have been substantially reduced. The performance of the algorithm has been quantified by comparing the uniformity between the uncorrected and the corrected phantom images. The results of the artifact reduction algorithm are indistinguishable from the true background value.
CONCLUSIONS: An efficient algorithm for MAR in seed brachytherapy was developed. The test results obtained using raw helical CT data for both phantom and clinical cases have demonstrated that the proposed MAR method is capable of accurately detecting and correcting artifacts caused by a large number of very small metal objects (seeds) in sinogram space. This should enable a more accurate use of advanced brachytherapy dose calculations, such as Monte Carlo simulations.},
keywords = {},
pubstate = {published},
tppubtype = {article}
}
METHODS: The approach for MAR is based on the interpolation of missing projections by directly using raw helical CT data (sinogram). First, an initial image is reconstructed from the raw CT data. Then, the metal objects segmented from the reconstructed image are reprojected back into the sinogram space to produce a metal-only sinogram. The Steger method is used to determine precisely the position and edges of the seed traces in the raw CT data. By combining the use of Steger detection and reprojections, the missing projections are detected and replaced by interpolation of non-missing neighboring projections.
RESULTS: In both phantom experiments and patient studies, the missing projections have been detected successfully and the artifacts caused by metallic objects have been substantially reduced. The performance of the algorithm has been quantified by comparing the uniformity between the uncorrected and the corrected phantom images. The results of the artifact reduction algorithm are indistinguishable from the true background value.
CONCLUSIONS: An efficient algorithm for MAR in seed brachytherapy was developed. The test results obtained using raw helical CT data for both phantom and clinical cases have demonstrated that the proposed MAR method is capable of accurately detecting and correcting artifacts caused by a large number of very small metal objects (seeds) in sinogram space. This should enable a more accurate use of advanced brachytherapy dose calculations, such as Monte Carlo simulations.