Dr. Malcolm McEwen

Adjunct Research Professor
Ionising Radiation Standards - National Research Council of Canada
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 Institute for National Measurement Standards – the National Metrological Institute for Canada. The Institute 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 two main categories:

  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 two linear accelerators at the NRC – a 3-40 MeV Vickers research accelerator and a 4-25 MeV Elekta clinical accelerator. 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 calorimetry.
  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 diodes and chemical dosimeters (e.g. alanine, 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.


  1. McEwen MR. Measurement of ionization chamber absorbed dose k(Q) factors in megavoltage photon beams. Med Phys. 2010 May;37(5):2179-93.
  2. Ross CK, McEwen MR, McDonald AF, Cojocaru CD, Faddegon BA. Measurement of multiple scattering of 13 and 20 MeV electrons by thin foils. Med Phys. 2008 Sep;35(9):4121-31.
  3. M.R. McEwen, I. Kawrakow and C.K. Ross, "The effective point of measurement of ionization chambers and the build-up anomaly in MV x-ray beams" Med. Phys. 35 950-958 (2008).
  4. D.J. La Russa, M.R. McEwen and D.W.O. Rogers, "An experimental and computational investigation of the standard temperature-pressure correction factor for ion chambers in kilovoltage x rays", Med. Phys. 34, 4690-4699 (2007).
  5. M.R. McEwen, H. Palmans and A.J. Williams,"An empirical method for the determination of wall perturbation factors for parallel-plate chambers in high-energy electron beams", Phys. Med. Biol. 51, 5167-5181 (2006).
  6. M.R. McEwen and D. Niven, "Characterization of the phantom material Virtual Water™ in high-energy photon and electron beams", Med. Phys. 33, 876-887 (2006).
  7. M.R. McEwen “Radiation Dosimetry for Oncology”, Encyclopedia of Medical Devices and Instrumentation 2nd Editon, ed. J G Webster Hoboken: John Wiley (2006).
  8. J. Helt-Hansen, A. Miller, S. Duane, P. Sharpe, M. McEwen and S. Clausen, "Calorimetry for dose measurement at electron accelerators in the 80–120 keV energy range", Radiat. Phys. Chem. 74, 354–371(2005).
  9. E. Tonkopi, M. McEwen, B. Walters and I. Kawrakow, "Influence of ion chamber response on in-air profile measurements in megavoltage photon beams", Med. Phys. 32, 2918-2927,(2005).
  10. J.P. McCaffrey, B. Downton, H. Shen, D. Niven and M.R. McEwen, "Pre-irradiation effects on ionization chambers used in radiation therapy" Phys. Med. Biol., 50, N121-N133 (2005).
  11. G.G.Zeng, M.R. McEwen, D.W.O. Rogers and N.V. Klassen N V, "An experimental and Monte Carlo investigation of the energy dependence of alanine/EPR dosimetry: II. Clinical electron beams", Phys. Med. Biol., 50, 1119-1129 (2005).