Novel Brachytherapy Technology • EngerLab

Mission

Brachytherapy is one of the most effective and precise radiation delivery modalities, where high activity radiation sources are placed directly into or near localized tumours using needles, plastic catheters or other specialized applicators giving a high radiation dose to the tumour while the dose to sensitive healthy tissues surrounding the tumour is lower. However, there are limitations with current clinical dose calculations algorithms, treatment planning, and delivery systems prohibiting delivery of a high dose to the tumour without dose spillage to surrounding healthy tissues. The Novel Brachytherapy Technology group is developing Monte Carlo-based treatment planning systems for conventional and intensity-modulated brachytherapy, intravascular brachytherapy, and ⁹⁰Y-based hepatic radioembolization as well as intensity-modulated brachytherapy delivery systems and novel radiation sources. The aim of research conducted by this group is to maximize and tailor the delivered radiation dose to the shape of the tumour and spare healthy tissues. This will increase the tumour control probability, while simultaneously reducing toxicity, which will increase the quality of life of the patients.

Members

Projects

Intensity Modulated Brachytherapy

Alana Thibodeau-Antonacci, Ph.D. Student & Marc Morcos, Ph.D. Student

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 has developed the next generation of high dose rate brachytherapy technology, including prototype delivery systems for intensity modulated brachytherapy treatment of prostate, cervix 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.

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, B.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

2021

Morcos, Marc; Antaki, Majd; Thibodeau-Antonacci, Alana; Kalinowski, Jonathan; Glickman, Harry; Enger, Shirin A.

RapidBrachyMCTPS: An open-source dose calculation and optimization tool for brachytherapy research Presentation

COMP, 01.06.2021.