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.
Intensity modulated brachytherapy system for dynamic modulation of shielded catheters Presentation
Radiotherapy and Oncology, 01.04.2018, ISSN: 0167-8140, 1879-0887.
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.
AIM-Brachy - 5 finalists out of 42 projects in McGill Clinical Innovation Competition and Hakim Family Prize. Miscellaneous
Top 5 abstract at the ESTRO annual meeting Miscellaneous
ESTRO Annual meeting, 2018.
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.
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.
Top ranking submission to the Young Investigator Symposium Presentation
COMP Annual meeting, Young Investigator Symposium, 01.01.2017.
Microdosimetric evaluation of intermediate-energy brachytherapy sources using Geant4-DNA Presentation
Radiotherapy and Oncology, 01.01.2017.
An intensity modulated delivery system for prostate brachytherapy using intermediate energy sources Presentation
Medical Physics, 01.01.2017.
A Novel Delivery System for High Dose Rate Intensity Modulated Brachytherapy with Intermediate Energy Brachytherapy Radiation Sources Such as 169Yb Presentation
Column generation-based Monte Carlo treatment planning for rotating shield brachytherapy Presentation
Radiotherapy and Oncology, 01.01.2016.
Production of Gd-153 as a source isotope for use in rotating shield high dose rate brachytherapy Presentation
Radiotherapy and Oncology, 01.01.2016.
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.
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.
Exploring (57)Co as a new isotope for brachytherapy applications Journal Article
In: Medical Physics, 39 (5), pp. 2342–2345, 2012, ISSN: 0094-2405.
Modeling a hypothetical 170Tm source for brachytherapy applications Journal Article
In: Medical Physics, 38 (10), pp. 5307–5310, 2011, ISSN: 0094-2405.
An algorithm for efficient metal artifact reductions in permanent seed Journal Article
In: Medical Physics, 38 (1), pp. 47–56, 2011, ISSN: 0094-2405.