Meet our students

Christopher Johnstone
Christopher’s research aims to standardize microCT image quality and to establish imaging dose in preclinical image-guided radiation therapy. He has also characterized a novel dosimeter for real-time small field measurements during his PhD at the University of Victoria.

Christopher Johnstone

Christopher Johnstone’s interest in Physics was sparked by a chance encounter with a book of historical biographies many years ago. Quickly flipping through the pages his eyes were met by a biography on Einstein describing the Theory of Relativity with respects to time travel. Having been a fan of the movie series Back to the Future, Christopher didn’t know anything about Physics, but if it could explain time travel to him, Physics was something he was willing to learn. Towards the end of his undergraduate education, his interest in Applied Physics was met with an interest in understanding cancer, with the merger of the two forming the beginnings of a career in Medical Physics.

He obtained his Master’s in Medical Physics at SDSU in California where he developed his research interests in absorbed radiation dose delivered by superficial therapy and CT imaging procedures. While the effects of high radiation doses are well established, there is not a consensus on the effects of low dose x-rays deposited in tissues.  

Christopher decided to continue his research interests by pursuing a PhD in Medical Physics here at UVIC, being fortunate to work with the prolific Dr. Magdalena Bazalova-Carter. While deciding which research project would be the best fit for him, he decided that there was a need for establishing microCT imaging standards in preclinical image-guided radiation therapy (IGRT). Preclinical IGRT advances our ability to treat cancers through translational research, and as currently, the community has no set standards to ensure that high microCT image quality is being used. High image quality is absolutely vital as the tiny anatomical structures of murine models require high resolution and high image quality for treatment planning and radiotherapy treatments.  

This research has led to a multi-institutional study published in Physics in Medicine & Biology that recommends quality assurance tolerance levels and microCT imaging standards for all commercial preclinical IGRT systems to follow. This work has resulted in attention within the community by having the prestigious honor of being a finalist at the national J.R. Cunningham Young Investigators Symposium at the 2016 Canadian Association of Medical Physicists (COMP) 62nd annual conference in St. John’s, Newfoundland.            

The imaging dose in preclinical IGRT may be high enough to affect the immune system and biological pathways of the animal, resulting in changes to the experimental outcome and results of a study. A complete knowledge of the absorbed dose to organs must be known to prevent experiments from being compromised from excess dose. After creating and validating a Monte Carlo model of the Small Animal Radiation Research Platform (SARRP), one of two commercial preclinical IGRT irradiators available, Christopher established dose to organs of murine subjects for a comprehensive report on imaging dose with varying imaging protocols. This research was also published in Physics in Medicine & Biology.  

Dosimetry in preclinical IGRT demands the ability to appropriately measure the small radiation fields (≤1 x 1 cm2) employed by these irradiators. Clinical ionization chambers are too large for these small field measurements and film does not offer real-time output. A need for an improved preclinical dosimeter was solved by the development and characterization of a novel scintillator dosimeter with a small 1 mm diameter and 1 mm long active polystyrene scintillating volume characterized to measure fields sizes down to 3 x 3 mm2. Correction factors were also obtained to correct for the energy dependence of the dosimeter for ≤ 220 kVp x-ray beams. This dosimeter is currently the only real-time dosimeter capable of measuring the small fields and energies demanded in preclinical IGRT. This work received significant attention from the community winning the 3rd place oral presentation award at the national J.R. Cunningham Young Investigators Symposium at the 2017 COMP 63rd annual conference in Ottawa, Ontario. This work has also been published in Medical Physics.    

Christopher is currently employed full time as a Research Medical Physicist at the University of Maryland School of Medicine while concurrently writing his PhD dissertation. His duties involve providing Medical Physics support for multi-million dollar contracts funding radiobiology studies to investigate radioprotectors to mitigate radiation damage in the body in the event of acute radiation exposure.   Here, he has also continuing publishing papers as he continues to contribute to research in the field of Medical Physics.

Discussing his time at UVIC, “I could not have accomplished any of this without the amazing support of my supervisor, Magdalena. Her drive in helping her students succeed is equal to none, and I have grown substantially as a scientist learning from her exceptional work ethic and her mastery of conducting research.” UVIC has also played a significant role in providing the necessary materials to allow its Medical Physics students to succeed, by teaching them to independently perform quality assurance on the LINACs at the BCCA, providing both preclinical and clinical equipment for research, and having an outstanding support team from the faculty at both UVIC and the BCCA. These experiences have primed Christopher for pursuing a career as a Medical Physicist where he is excited to make a positive impact in people’s lives.         

 

Publications

  1. CD Johnstone, F Therriault-Proulx, L Beaulieu, and M Bazalova-Carter. Characterization of a Plastic Scintillating Detector for the Small Animal Radiation Research Platform (SARRP). Medical Physics, 446(1), 2019).
  2. Y Poirier, CD Johnstone, C Kirby. The Potential Impact of Ultrathin Filter Design on Dosimetry and Relative Biological Effectiveness in Modern Image-Guided Small Animal Irradiators. The British Journal of Radiology, 91(20180537), 2018.
  3. NM Esplen, L Chergui, CD Johnstone, and M. Bazalova-Carter. Monte Carlo Optimization of a Microbeam Collimator Design for the use on the Small Animal Radiation Research Platform (SARRP). Physics in Medicine & Biology, 63(17), 2018.
  4. CD Johnstone and M Bazalova-Carter. MicroCT Imaging Dose to Mouse Organs Using a Validated Monte Carlo Model of the Small Animal Radiation Research Platform (SARRP). Physics in Medicine & Biology, 11(63), 2018.
  5. CD Johnstone, P Lindsay, EE Graves, E Wong, JR Perez, Y Poirier, Y Ben-Bouchta, T Kanesalingam, H Chen, AE Rubinstein, K Sheng, and M Bazalova-Carter. Multi-institutional MicroCT Image Comparison of Image-Guided Small Animal Irradiators. Physics in Medicine & Biology, 14(62), 2017.
  6. CD Johnstone, R LaFontaine, Y Poirier, and M Tambasco. Modeling a Superficial Radiotherapy X-ray Source for Relative Dose Calculations, Journal of Applied Clinical Medical Physics. 16(3), 2015.

Presentations

  1. CD Johnstone and M Bazalova-Carter. MicroCT Imaging Dose for a Commercial Image-Guided Small Animal Irradiator (Talk), COMP 64th Annual Scientific Meeting, Montreal, Quebec, Canada, September 12-15, 2018. 
  2. CD Johnstone and M Bazalova-Carter. Establishing MicroCT Imaging Dose to Mouse Organs using a Validated Monte Carlo Model of the Small Animal Radiation Research Platform (Talk), AAPM 59th Annual Meeting, Denver, Colorado, USA, July 30 – August 3, 2017.
  3. CD Johnstone. L Beaulieu, F Therriault-Proulx, and M Bazalova-Carter. Development and Characterization of a Plastic Scintillating Detector for Small Animal Irradiators (Talk), COMP 63rd Annual Scientific Meeting, Ottawa, Ontario, Canada, July 12 – 15, 2017.  
  4. CD Johnstone and M Bazalova-Carter. Establishing Imaging Standards for Image-Guided Small Animal Irradiators (Poster), CAMTEC, University of Victoria, Victoria, Canada, December 10, 2016.
  5. CD Johnstone and M Bazalova-Carter. Automated Quality Assurance for Image-Guided Small Animal Irradiators (Talk), COMP 62nd Annual Scientific Meeting, St. John’s, Newfoundland, Canada, July 20-23, 2016.    
  6. CD Johnstone, R LaFontaine, Y Poirier, and M Tambasco. Validation of In-House Dose Calculation Software for Superficial Therapy (Poster), CARO/COMP Joint Scientific Meeting, Montreal, Quebec, Canada, September 18 – 21, 2013.

Awards

  • 2017 COMP J.R. Cunningham Young Investigator Competition, 3rd Place, Ottawa, Ontario, Canada. (International, $250)
  • 2017 British Columbia Cancer Agency Travel Award, University of Victoria. (Institutional, $500)
  • 2017 Ideafest 360, Best Talk Finalist, University of Victoria. (Institutional)
  • 2016 COMP J.R. Cunningham Young Investigator Competition, Finalist, St. John’s, Newfoundland, Canada. (International)
  • 2016 CUPE Conference Award, University of Victoria. (Institutional, $250)
  • 2015 University of Victoria Graduate Award, University of Victoria. (Institutional, $3,000)
  • 2014 University of Victoria Fellowship, University of Victoria. (Institutional, $15,000)
  • 2013 National Science Foundation Award, San Diego State University. (National, $5,000)
  • 2013 COMP Salsa Travel Award, University of Calgary. (Institutional, $500)
  • 2013 Graduate Student Travel Fund, San Diego State University. (Institutional, $500)
  • 2012 Skolil Scholarship Physics Fund, San Diego State University. (Institutional, $700)
  • 2012 General Fund Student Scholarship, San Diego State University. (Institutional, $300)
  • 2011 Dean’s List, California State University, Fullerton. (Institutional)