Physics News and Events

1 Aug 2017 - 11:30am

Presenter: Laura Liao
Supervisor: Dr. Catherine Beauchemin


In this work, two studies were performed where mathematical models (MM) were used to re-examine and refine quantitative methods based on in vitro assays of influenza A virus infections.

In the first study, we investigated the standard experimental method for counting defective interfering particles (DIPs) based on the reduction in standard virus (STV) yield (Bellett & Cooper, 1959). We found the method is valid for counting DIPs provided that: (1) a STV-infected cell's co-infection window is approximately half its eclipse phase (it blocks infection by other virions before it begins producing progeny virions); (2) a cell co-infected by STV and DIP produces less than 1 STV per 1,000 DIPs; and (3) a high MOI of STV stock (>4 plaque-forming units/cell) is added to perform the assay. Prior work makes no mention of these criteria such that the method has been applied incorrectly in several publications discussed herein. We determined influenza A virus meets these criteria, making the method suitable for counting influenza A DIPs.

In the second study, we compared a MM with an explicit representation of viral release to a simple MM without explicit release, and investigated whether parameter estimation and the estimation of neuraminidase inhibitor (NAI) efficacy were affected by the use of a simple MM. Since the release rate of influenza A virus is not well-known, a broad range of release rates were considered. If the virus release rate is greater than ~0.1 /h, the simple MM provides accurate estimates of infection parameters, but underestimates NAI efficacy, which could lead to underdosing and the emergence of NAI resistance. In contrast, when release is slower than ~0.1 /h, the simple MM accurately estimates NAI efficacy, but it can significantly overestimate the infectious lifespan (i.e., the time a cell remains infectious and producing free virus), and it will significantly underestimate the total virus yield and thus the likelihood of resistance emergence. We discuss the properties of, and a possible lower bound for, the influenza A virus release rate.

Overall, MMs are a valuable tool in the exploration of the known unknowns (i.e., DIPs, virus release) of influenza A virus infection.

Posted by Graham, Jul-31-2017

The Department of Physics wishes to congratulate alumna Christiane Burton who on July 13th was awarded the Sylvia Fedoruk prize!

The prize is presented for the best paper on a subject falling within the field of medical physics, relating to work carried out wholly or mainly within a Canadian institution and published during the past calendar year. The award was given at the Canadian Organization of Medical Physicists (COMP) in Ottawa, Ontario, Canada.

From the Canadian Association of Medical Physicists website:


During her 35 years of service, Dr. Fedoruk brought honour to her country, her home province, the medical physics community, all the while maintaining a "down to earthness" which distinguishes her as a "people person". These qualities contributed to her receiving awards such as Saskatoon's Woman of the Year, The Order of Canada, and Saskatchewan's Award of Merit, all in 1986. That same year, she was elected Chancellor of the University of Saskatchewan, and in 1995 she completed a 5-1/2 year term as Saskatchewan's Lieutenant Governor. Dr. Fedoruk was inducted into the Canadian Medical Hall of Fame in 2008.

In 1986, the Saskatchewan Cancer Agency established the Sylvia Fedoruk Prize in Medical Physics to honour Dr. Fedoruk for her 35 years of dedicated and distinguished service to Saskatchewan's cancer program. This prize is presented for the best paper on a subject falling within the field of medical physics, relating to work carried out wholly or mainly within a Canadian institution and published during the past calendar year. The award consists of a plaque and a cash prize. The prize was first awarded in 1988. Selection is made by an anonymous panel of judges appointed by the Canadian Organization of Medical Physicists.

Posted by Graham, Jul-19-2017
14 Jul 2017 - 8:00am

Presenter: Celina Yang
Doctor of Philosophy, Biomedical Physics
Ryerson University, 2017

Supervisor: Dr. Devika Chithrani and Dr. Michael Kolios

This dissertation presents the effect of peptide-modified 10 nm colloidal gold nanoparticles (GNPs) with chemotherapeutic drugs, bleomycin and cisplatin, and 6 MV X-ray irradiation in a breast cancer cell-line, MDA-MB-231, in vitro. The GNPs were stabilized with a pentapeptide (Cys-Ala-Lys-Asp-Asp) and modified with a peptide sequence containing a ‘RGD’ amino acid motif (H-Cys-Lys-Lys-Lys-Lys-Lys-Lys-Gly-Gly-Arg-Gly-Asp-Met-Phe-Gly-OH). Bleomycin binds to the surface of the GNPs through a thiol bond and cisplatin has no significant interaction with the GNP surface.

Gold nanoparticle concentration used in studies throughout this dissertation was 0.3 nM. No significant toxicity was induced by introducing GNPs to MDA-MB-231 cells at this concentration. To examine the variability of accumulation of GNP constructs with the presence of chemotherapeutics, the amount of gold (Au) atoms were measured with Inductive Coupled Plasma-Atomic Emission Spectroscopy (ICP-AES). There was no significant difference in the accumulation of GNPs in the presence of cisplatin. There was a 5 % decrease in accumulation of GNPs in cells with bleomycin. However, the 5 % decrease with bleomycin was still a 6-fold increase compared to the accumulation of unmodified GNPs in cells. These results suggest that with the peptide modification, the presence of chemotherapeutics do not significantly affect the accumulation of GNPs into cells.

The effect of having GNPs with chemotherapeutics (either bleomycin or cisplatin) was examined through clonogenic and immuofluorscence assays. The conjugation of bleomycin onto peptide modified GNPs decreased the survival of MDA-MB-231 cells by 22.5 % (P < 0.05) compared to treatment with the same concentration of free bleomycin (without GNPs). On the contrary, treating cells with GNPs and cisplatin did not have a significant difference in survival compared to the same concentration of free cisplatin treatment (p = 0.078). This suggests that conjugating chemotherapeutics onto the GNPs can result in a more efficient delivery of the drug. If the drug does not bind to the GNP surface, having GNPs in the media does not interfere with the uptake of the drug.

The effect of radiosensitization in the presence of peptide modified GNPs was studied using 6 MV X-rays. The MDA-MB-231 cells were incubated with 0.3 nM peptide modified GNPs 16 hours prior to irradiation with 2 Gy of 6 MV X-rays. The survival fraction decreased by 23 % (p < 0.05) compared to the cells treated with same volume of phosphate buffed saline (PBS) solution prior to radiation. This confirms radiosensitization from the modified GNPs at a low concentration (0.3 nM) with clinically relevant energies (6 MV).

Lastly, the triple combined effect of modified GNPs, chemotherapeutics, and irradiation was investigated. The MDA-MB-231 cells were treated with modified GNPs, a chemotherapeutic (either bleomycin or cisplatin) and 2 Gy of 6 MV radiation to investigate the effect of triple combined therapy. The presence of GNPs had an advantage to the combined chemotherapy and radiation therapy. Based on results from these studies, peptide-modified GNPs can be used in addition to combined chemotherapy and radiation therapy for improved outcomes in cancer treatment.

Posted by Graham, Jun-30-2017
30 Jun 2017 - 10:00am

Presenter: Ermias Woldemichael
M.Sc., Biomedical Physics, Ryerson University, 2017

Supervisor: Dr. Vladislav Toronov


Hyperspectral near infrared spectroscopy (hNIRS) is a noninvasive, real-time imaging modality with an improved quantitative accuracy and increased number of detectable chromophores. It uses the broadband spectrum of light wavelengths in the range of 700 – 1100 nm and is based on the unique absorbance property of molecules and the fact that all biological tissues are relatively transparent to these wavelengths which allow for measuring concentrations of light absorbing molecules such as the Oxy- and Deoxy- hemoglobin and Cytochrome C Oxidase. As opposed to fMRI, PET and SPECT, hNIRS is inexpensive and portable.

The purpose of this thesis project was to employ advantages of hNIRS by developing the multichannel hNIRS set-up for the simultaneous assessment of multiple areas of the brain and to test the system in clinical applications. To achieve these goals, I developed a new optical fiber bundle design providing improvement of the optical power throughput into the hNIRS light detectors. I also developed a novel probe for measurements on hairy areas of the human head. To validate the hNIRS system I used it simultaneously with fMRI, which revealed a good correlation of hNIRS and fMRI BOLD signals from the brain. The multichannel hNIRS set up with the increased signals due to the novel optical fiber bundles was then used during various brain activation protocols, which in the future can allow for the assessment of patients with mild traumatic brain injuries. Finally, the hNIRS system with new fiber bundles was compared with a commercial NIRS system in clinical setting for brain monitoring of patients during the transcatheter aortic valve implantation operation.

Posted by Graham, Jun-30-2017
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


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


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