Dr. Malcolm McEwen

Adjunct Research Professor
Ionising Radiation Standards - National Research Council of Canada
1200 Montreal Rd.
Ottawa, K1A 0R6
(613) 993-2197 Ext. 226
Malcolm [dot] McEwenatnrc-cnrc [dot] gc [dot] ca

Research Summary
The Ionizing Radiation Standards (IRS) Group at the NRC is part of the Metrology Research Centre, which forms the National Measurement Institute for Canada. The Research Centre maintains and disseminates standards of measurement – time, length, mass, temperature, etc – to Canadian organisations (e.g. industry, university, government). IRS is responsible for standards of radiation absorbed dose and my work falls into three main areas:

1. Development of calorimetric absorbed-dose standards for electron and photon beam dosimetry. The primary area of focus at present is water calorimetry in clinical photon and electron beams, which in terms of precision, accuracy and experimental constraints is a very challenging measurement problem. For this work we maintain and operate three linear accelerators at the NRC – a 3-40 MeV Vickers research accelerator and two Elekta clinical accelerators (one with full IGRT capability). A significant amount of investigative work has gone into ensuring that these accelerators can produce the very stable and reproducible radiation beams that are necessary for primary standards-level experiments.

2. Experimental and theoretical work on the performance and calibration of secondary dosimeters in megavoltage photon and electron beams - in particular ionization chambers, but also solid-state detectors and chemical dosimeters (particularly alanine and Fricke). Primary devices such as calorimeters are generally restricted to the primary standards laboratory and for measurements “in the field” some kind of secondary dosimeter is required. There are a large number of different systems to choose from and the work we do within IRS in this area includes accurate characterization of new devices, development of new or existing instruments and investigation of the physical underpinnings of dosimetry systems. This work has led to new recommendations in international dosimetry protocols.

3. Benchmarking of Monte Carlo-based radiation simulations. Monte Carlo radiation transport systems, such as the EGSnrc package maintained by the IRS group, use a range of interaction data sets and implement a number of different transport algorithms. Accurate benchmarking of MC simulations with carefully-designed experiments can provide confirmation of theoretical calculations and indicate where improvements in simulations are required.

1. A Bourgouin, C Cojocaru, C Ross and M McEwen, “Determination of Wair in high-energy electron beams using graphite detectors”, Med. Phys. 46 (2019)
2. T Roy, F Tessier and M R McEwen, “A system for the measurement of electron stopping powers: proof of principle using a pure β-emitting source”, Rad. Phys. Chem. 149, 134-141 (2018)
3. C Salata, M David, C De Almeida, I El Gamal, C Cojocaru, E Mainegra-Hing, M McEwen, “Validating Fricke dosimetry for the measurement of absorbed dose to water for HDR 192Ir brachytherapy: a comparison between primary standards of the LCR, Brazil, and the NRC, Canada”, Phys. Med. Biol. 63 085004 (2018)
4. B R Muir and M R McEwen, “Technical Note: On the use of cylindrical ionization chambers for electron beam reference dosimetry”, Med. Phys. 44 (2017)
5. B R Muir, C D Cojocaru, M R McEwen, and C K Ross, “Electron beam water calorimetry measurements to obtain beam quality conversion factors”, Med. Phys. 44 (2017)
6. J D Ververs, M R McEwen and J V Siebers, “Quantitative ionization chamber alignment to a water surface: Performance of multiple chambers”, Med. Phys. 44 3939 (2017)
7. M R McEwen and J Taank, “Examining the Influence of Environmental Corrections on Ionization Chamber Performance”, Med. Phys. 44, 694 (2017)
8. D B Flint, D A Granville, N Sahoo, M McEwen, G O Sawakuchi, “Ionization density dependence of the curve shape and ratio of blue to UV emissions of Al2O3:C optically stimulated luminescence detectors exposed to 6-MV photon and therapeutic proton beams”; Radiat. Meas. (2016)
9. M Chamberland, M R McEwen and Tong Xu, “Technical aspects of real time positron emission tracking for gated radiotherapy”, Med. Phys. 43, 783 (2016)
10. D T Burns, C Kessler, E Mainegra-Hing, M R McEwen, “Key comparison BIPM.RI(I)-K3 of the air-kerma standards of the NRC, Canada and the BIPM in medium-energy x-rays”, Metrologia 53 (2016)
11. J Renaud, A Sarfehnia, K Marchant, M McEwen, C Ross and J Seuntjens, “Direct measurement of electron beam quality conversion factors using water calorimetry”, Med. Phys. 42, 6357 (2015)
12. R Ganesan, M R McEwen and C G Orton, “Point-counterpoint: Calibration of radiotherapy ionization chambers using Co-60 is outdated and should be replaced by direct calibration in linear accelerator beams”, Med. Phys. 42, 5003 (2015)
13. I El Gamal, C Cojocaru, E Mainegra-Hing and M McEwen, “The Fricke dosimeter as an absorbed dose to water primary standard for Ir-192 brachytherapy”, Phys. Med. Biol. (2015)
14. M McEwen, P Sharpe and S Voros, “Evaluation of alanine as a reference dosimeter for therapy level dose comparison in megavoltage electron beams” Metrologia 52 272-279 (2015)
15. E S M Ali, B Spencer, M R McEwen and D W O Rogers, “Towards a quantitative, measurement-based estimate of the uncertainty in photon mass attenuation coefficients at radiation therapy energies”, Phys. Med. Biol. 60 1641–1654 (2015)