Physics News and Events

22 Jun 2017 - 10:00am

Presenter: Raphael Jakubovic M.Sc., PhD Candidate
Department of Biomedical Physics
Ryerson University & Sunnybrook Health Sciences Centre

Supervisors: Dr. Victor Yang, Dr. Ana Pejović-Milić

Abstract:

The objective of high dose stereotactic radiotherapy regardless of application is to treat the malignancy while minimizing the dose to the surrounding healthy tissue. In the context of spinal tumours this paradigm is difficult since the rigid dose tolerance of the spinal cord precludes optimal dose coverage of the epidural disease near the spinal cord. To achieve adequate coverage spine separation surgery is performed, increasing the distance from the spinal cord to the malignancy and facilitating adequate radiation treatment planning. This approach has been validated with delivery of maximum tolerable dose and local control rates over 90\%.

The objective of this dissertation is to establish the feasibility of intra-operative, dose guided, spine separation surgery. In the current clinical context, spine separation surgery is performed prior to radiation treatment planning and contours are placed based on post-operative resected tumour volumes. The extent of surgical resection is not dictated by the dosimetric constraints of the spinal cord and relies solely on the clinical expertise of the operating neurosurgeon. Further, though a skilled surgeon can perform precise tumour debulking with or without the aid of millimetre resolution neuro-navigation devices, determination of surgical debulking progress with accuracy comparable to treatment delivery cannot be recognized without intra-operative imaging. To achieve this goal, we introduced pre-surgical dosimetric planning with tracked high frequency ultrasound imaging into the operating theatre to inform the surgeon of the surgical progress while considering the dosimetric objectives.

In this dissertation, we assessed the dosimetric advantage of spine separation surgery on a millimetre by millimetre basis in a retrospective review. Feasibility of intra-operative navigation with submillimetre resolution was established by quantifying the application accuracy of surgical navigation in the context of cranial and spinal surgery. Accuracy quantification was performed, assessing our revolutionary optical surface imaging system and benchmarked versus existing commercially available neuro-navigation systems. Finally, to establish feasibility we integrated a high frequency ultrasound system into the operating theater during spine separation surgery. Thus, by implementing sub-millimetre high-frequency ultrasound imaging and neuro-navigation, incremental gains towards establishing the feasibility of intra-operative dose planning by iteratively updating the extent of tumour resection were recognized.

Posted by Graham, Jun-19-2017

By Charlotte Ferworn

Ryerson’s Medical Physics students attending CCUWiP 2017.
From the left, Amun Sihra, Preet Kahlon, Megan Dagys,
and Charlotte Ferworn.
Posted by Graham, Mar-28-2017
20 Mar 2017 - 1:30pm

Presented: Dr. Soo Hyun Byun, Associate Professor
Department of Physics and Astronomy
Radiation Sciences Graduate Program
McMaster University

Abstract:

In order to address the fundamental physics problems encountered in radiation detection and dosimetry, my research group has focused on advanced gaseous radiation detector and signal processing system developments. A gaseous detector is one of the popular radiation detection methods and there has been outstanding progress in its technology in the last decade. Since 2008, my group has been developing THick Gas Electron Multiplier (THGEM) detectors which offer unique features in contrast to traditional gaseous proportional counters. In this talk, I will briefly review the underlying physics on THGEM and present our THGEM detectors geared for imaging and dosimetry. Another amazing project that we are currently working on is “McMaster NEUtron DOSimetry and Exploration (NEUDOSE)”, which aims at designing and building a satellite for measuring neutron and charged particle dose rates in low-Earth orbit. I will present the unique features of the NEUDOSE design and major accomplishments.

For any kind of radiation detectors, the importance of signal processing can never be overemphasized. With the recent progress in digital electronics, detector signal processing has been dramatically improved over the classical analog processing. I will present our recent signal processing systems that have been developed for a variety of radiation detectors.

Posted by Graham, Mar-06-2017
23 Feb 2017 - 1:00pm

Presented by: Dr. Julia Bernatska
Hosted by: Dr. Alexandre Douplik

Dr. Julia Bernatska is an Associate Professor (since 2005) and the Chair (since 2014) of Department of Physical and Mathematical Sciences at National University of Kyiv Mohyla Academy (Ukraine). Currently, Dr. Bernatska is a visiting professor of the Department of Mathematics and Statistics at Concordia University, Montreal.

Posted by Graham, Feb-23-2017
27 Mar 2017 - 1:30pm - 3:00pm

Presenter: Chris Meyer
York Mills Collegiate Institute, Toronto
VP Teaching and Learning, Ontario Association of Physics Teachers

Abstract:
We live in an exciting time for teaching physics. Over 30 years of education research by physics professionals is transforming physics teaching from a mystical art into a practical science. In the process, many educational myths have been successfully challenged. Research is providing great insight into the cognitive development of our students’ physics understanding and the accompanying physical changes that take place in the brain. As a result, pedagogical techniques have broken free from the traditions and fads of the past, and are becoming grounded in an empirical understanding of how humans learn. By creating a research-based learning environment, we can literally build better students and build better teachers. In this talk, Chris will share the key results from education research that inspired him to create a lecture-free high school physics program that is now spreading across Ontario.

Bio:
Chris Meyer leads a reformed grade 11 and 12 physics program at York Mills Collegiate Institute in Toronto. He has presented pedagogical workshops for high schools and universities across southern Ontario, and his classroom resources are used throughout Canada and the United States. Chris is the winner of the 2016 CAP Award for Excellence in Teaching High School/CEGEP Physics (Ontario) and the 2015 Toronto District School Board Teaching Excellence Award. His most recent article, Group Work Test for Context Rich Problems appeared in the May 2016 edition of The Physics Teacher. When Chris takes off his physics hat, he enjoys writing orchestral music, with recent performances by the Toronto Symphony Orchestra and the National Youth Orchestra of Canada. To learn more, please visit: www.meyercreations.com/physics

Posted by Graham, Feb-13-2017
13 Feb 2017 - 12:00pm

Please join us for the Biomedical Physics Seminar Series.

TITLE: OPTICAL STUDY OF HEMOGLOBIN FORM CONVERSIONS OF BIOTISSUE OPTICAL AND OPTOACOUSTIC PHANTOMS
Student: Xiao Juan Zheng
Supervisor: Dr. Alexandre Douplik

ABSTRACT: Hemoglobin (Hb) molecules present in red blood cells have several critical roles in addition oxygen transportation to tissue. Hb carries photosensitizer substances in photodynamic therapy, though the interaction of the heme group with the light and the substrate resulting in oxygen reactive species. Optical and optoacoustic imaging (OA) are sensitive to different forms of Hb due to the relative strong absorption of Hb. . Light propagation can have significant impact in optical and OA specially in using multi wavelengths approach to detect different forms of Hb. Monitoring hemoglobin (Hb) remains challenging specially in the presence of the reactive oxygen species as it reacts with oxyhemoglobin (oxy-Hb) to form methemoglobin (Met-Hb), another form of hemoglobin. This study will focus on Hb forms conversion in liquid and silicon based phantom. Human Met-Hb sample was obtained by dissolving the lyophilized powder in phosphate buffered saline (PBS), later converted to deoxyhemoglobin (deoxy-Hb) and oxy-Hb. The different Hb forms were validated by measuring its optical absorption (from 300-1000 nm), then compared and confirmed with absorption spectra from Oregon Medical Laser Center (OMLC). Blood containing silicon phantoms with photosensitizer additive were created to conduct photochemical reaction of reducing oxy-Hb to deoxy-Hb. This involved irradiating the phantoms to active the photochemical reaction. The efficiency of various photosensitizer concentrations and irradiation time was determined by measuring the optical absorption (from 300-1000 nm) in each phantom.


TITLE: IN VIVO DETECTION OF LANTHANUM VIA X-RAY FLUORESCENCE
Student: Joanna Nguyen
Supervisor: Dr. James Grafe

ABSTRACT: Lanthanum (La) is a rare-earth metal used in phosphate binders in the form of a chewable tablet called lanthanum carbonate (LaC), commercially known as Fosrenol®. The daily high intake of LaC in patients with end-stage kidney disease is needed to reduce serum phosphate concentrations within normal range. Past studies have employed invasive bone biopsy sampling to show La accumulation in bone after long-term administration of LaC. However, the potential risks associated with long-term bone retention of La are unknown. In this work, we investigate the feasibility of using a K X-ray Fluorescence (K-XRF) spectroscopy system to quantitatively and non-invasively measure in vivo bone La. A series of hydroxyapatite (HAp) bone mineral phantoms doped with various concentrations of La were created to represent human bone. The HAp phantoms were placed in a 90° geometry relative to a bulky 1.11 GBq 241Am excitation source and high-purity germanium detector. For a live-time measurement of 2000 s, the initial minimum detection limit (MDL) was calculated to be 2.32 μg La/g Ca or 0.93 μg La/g HAp. However, for a newly acquired lead-collimated 241Am source, the MDL improved to 1.9 μg La/g Ca or 0.75 μg La/g HAp. This improvement in the MDL shows promising results and demonstrates the capabilities of this system as a non-invasive technique to monitor the long-term accumulation of La in bone. To the best of our knowledge, this is the first reported work that seeks to non-invasively measure bone La via in vivo XRF.

Posted by Kevin, Feb-09-2017
9 Feb 2017 - 11:30am

Presenter: Ruben N. Pinto
M. Sc. Biomedical Physics

Abstract:

Significant functional/structural changes of red blood cells (RBCs) have been documented during its in vitro storage. Collectively termed as RBC storage lesions, changes include an increase in RBC oxygen saturation (SO2) and an increase in irreversibly damaged RBCs (spheroechinocytes). In this work, novel optical techniques are presented for determining the spheroechinocyte population as a function of storage time via automated image flow cytometry (IFC) morphology characterization, and the acquisition of RBC SO2 via an in situ photoacoustic (PA) method. Blood gas analysis (BGA) was used as the gold standard SO2 measure. Over the lifespan of seven blood bags, the IFC spheroechinocyte population – PA SO2 correlation was found to be strong (0.60 < r2 < 0.91). These results suggest that monitoring SO2 changes can potentially infer the rate of increase of irreversibly damaged RBCs. A very strong PA SO2 – BGA SO2 correlation (r2 > 0.95) shows high potential for in situ monitoring of RBC storage lesions.

Posted by Graham, Feb-06-2017
6 Feb 2017 - 12:00pm

Please join us for the Biomedical Physics Seminar Series.

TITLE: DOSIMETRIC STUDY OF PD-103 CORE GOLD NANOPARTICLES
Student: Daniel Dicenzo
Supervisors: Dr. Claire McCann & Dr. Carl Kumaradas

ABSTRACT: Low dose rate (LDR) brachytherapy is a common radiation treatment and has been used to treat breast cancer. LDR brachytherapy uses radioisotopes permanently inserted into the breast to deliver a prescribed radiation dose over a long period of time (months). Radioisotopes used in this treatment include Iodine-125 and Palladium-103 (Pd-103). These isotopes release photons at average energies of 28 keV and 21 keV respectively. An advantage of LDR brachytherapy to conventional external beam radiation therapy is that LDR brachytherapy can provide a localised radiation dose to the target volume without the need to pass through as much healthy tissue. This treatment also requires a single surgery allowing for one continuous radiation treatment deposited over a period of months. A drawback to the conventional use of brachytherapy sources is the inhomogeneity of dose deposition. This can result in underdosing to certain areas, allowing for the possibility of cancer recurrence. To ensure a more homogeneous dose distribution, more effective techniques need to be investigated.
Currently, a popular method being investigated to improve radiotherapy is the use of gold nanoparticles (GNP) in conjunction with radiation. GNPs have been widely shown to enhance radiation dose due to the greater number of charged particles produced when radiation interacts with the gold. The small size and biocompatibility allow for GNPs to be delivered to a tumor to enhance the delivered dose. By producing radioisotopes inside gold nanoparticles and placing them in a dissolvable seed (to be injected into the breast), it is possible that the controlled diffusion of the nanoparticles can provide a more homogeneous dose distribution than with conventional LDR seeds. Furthermore, the ability for the nanoparticles to enter cells may allow for greater cell death due to the close proximity of the nanoparticles to the cell’s nucleus.

This study will investigate dose deposition in breast cancer cells using Pd-103 nanoparticles coated in gold. Monte Carlo code will be used to simulate the radiation emitted from a Pd-103 GNP. This will allow us to calculate the dose absorbed in a cell when exposed to the nanoparticles. Furthermore one can determine the dose absorbed in a group of cells and evaluate cell survival. The future plan of this study is to evaluate GNP distribution and dose to a tumor when the nanoparticles are placed in a dissolvable brachytherapy seed.


TITLE: ELEMENTAL MAPPING OF STRONTIUM IN RATS TREATED WITH STRONTIUM RANELATE AND STRONTIUM CITRATE USING 2D XRF AND 3D DUAL ENERGY K-EDGE SUBTRACTION IMAGING
Student: Daniel Cardenas
Supervisors: Dr. Ana Pejovic-Milic

ABSTRACT: Osteoporosis is a debilitating disease that leads to the loss of bone mass, which is a very prevalent health problem in the northern countries such as Canada. Strontium based medications, such as strontium ranelate (Protelos R ), have been indicated to treat and alleviate the condition. On the other hand, strontium salts that are available o -shelf in stores in Canada, have been assumed to provide similar e ffects to the strontium medication. The objective of this study was to compare the distribution of strontium in animal bones following administration of strontium ranelate and
strontium citrate.
Sprague-Dawley female rats were dosed with the two strontium salts; six animals received strontium ranelate, seven received strontium citrate, and six were left as the control group. Rats were dosed daily over ten weeks; the strontium ranelate and strontium citrate group received 174.3 mg/kg/day and 235.7 mg/kg/day of elemental Sr, respectively; the strontium citrate group received 35% more elemental Sr. A right humerus was collected from all animals and measured for strontium distribution using 2D XRF in Atominstitut, Institute for Atomic and Subatomic Physics, Vienna, Austria and 3D Dual Energy K-edge Subtraction Imaging available at the Canada Light Source, Saskatoon, Saskatchewan. Fresh bones were submerged in 70% ethanol and shipped to Vienna for a sample preparation. Three thin (10 - 20 m) slices from each of the groups were analyzed by 2D scanning diff erent regions of interest containing trabecular and cortical bone using a Rh anode tube (Microfocus Oxford "Apogee", 20 W maximum power). The scanning parameters used were a step-size of 50  50 m2 acquisition time of 100 s per point, the x-ray tube was set to a current of 0.4 mA and a voltage of 50 kV. The measurements yielded maps for Ca, Sr, P, S, and Zn. The Ca maps between the two Sr-treated groups showed similar intensities, which would suggest similar levels of calci cation. Sr signals were detected in the Sr-treated groups; while no detectable signal was observed in the control sample. The accumulation of strontium can be seen primarily in the
trabecular or inner region of the bones in both groups.

Samples measured at Canadian Light Source were also defatted in ethanol solution for two weeks and air dried for one week, prior to the measurement. The samples were cut down into 2 - 3 mm thick slices using a diamond wafering blade in order to allow the flux of photons to penetrate adequately. Eight samples from the strontium citrate, strontium ranelate, and control groups were scanned using the BioMedical Imaging and Therapy (BMIT-BM) beamline, the source-to-sample
distance was 25 m while the sample-to-detector distance was 0.2 m. Two sets of data were obtained for each bone using computed tomography (CT) imaging every 0.1 over 180 at two energies, one below and the second one above the K-edge of strontium of 16.105 keV. The resultant images were co-registered and subtracted in order to obtain the Sr maps. These maps provided a spatial distribution as well as concentration (mg/cm3) of elemental Sr in the calci ed tissue of the rat bones. Sr was observed to be largely present in the trabecular regions near the epiphyseal plate in both the Sr-treated groups, while the level of Sr in the control bones was below or close to the detection limit.

Our work will present the 2D spatial distribution of Sr and other elements from XRF, as well as the 3D spatial distribution with quanti cation of Sr from dual energy K-edge subtraction imaging in the bones of rats treated with Sr ranelate and citrate in comparison to the control.

Posted by Kevin, Feb-02-2017