Medical Physics Graduate Program Faculty

Brad Warkentin

Brad Warkentin, PhD, FCCPM

Associate Professor, Division of Medical Physics, Department of Oncology, University of Alberta

Medical Physicist, Dept. of Medical Physics, CCI

Member: Canadian College of Physicists in Medicine

Research Interests

Synchrotron-based Radiotherapy Applications: Microbeam Radiotherapy

The Canadian Light Source (CLS) in Saskatoon is one of a handful of x-ray synchrotrons worldwide with dedicated biomedical beamlines. The beamlines offer novel imaging and radiotherapy modalities that exploit the unique beam characteristics, which include extreme flux rates, minimal beam divergence, monochromaticity, and coherence. One of my primary research interests is exploring the potential of microbeam radiotherapy (MRT), a preclinical form of RT using large doses (100’s of Gy) of extremely small slits of radiation (~ 50 μm). Preliminary cellular and animal studies have shown a remarkable tolerance of normal tissues to such deliveries, motivating further research into its use as a potential alternative therapy for specific human cancers (e.g. pediatric brain cancers). Due to the large doses rates, low beam energies and tiny beams, accurate knowledge of MRT dose distributions is a significant challenge. Our current research has focused on improving and developing the techniques for MRT dosimetry.

MR-Linac: Monte Carlo Dosimetry

Another recent research interest of mine is further developing the Monte Carlo modeling infrastructure for calculating radiotherapy dose distributions in the presence of the magnetic fields used with the MR-linac system at the Cross Cancer Institute. Future work may include incorporating the dosimetric effects of the magnetic fields in the IMRT optimization process.

Radiobiological Modeling

Radiobiological modeling aims to characterize and (hopefully) predict tumor response and normal tissue complication rates to radiotherapy in a quantitative manner so that better patient-specific treatment optimization can be achieved. However, current models are generally simplistic and have limited predictive power. I’m interested in exploring the limitations of current models, and developing improved models. A particularly interesting avenue investigation is the modeling of MRT response, and how it may be applied to more conventional modalities.

Selected Publications

D.L. Anderson, R. Mirzayans, B. Andrais, L.A. Siegbahn, B.G. Fallone, B. Warkentin,
"Spatial and temporal distribution of γH2AX fluorescence in human cell cultures following synchrotron-generated x-ray microbeams: Lack of correlation between persistent γH2AX foci and apoptosis",
J Synchrotron Radiation, 21(4), pp.801-810 (2014),
PubMed Link

D. Anderson, B. Andrais, R. Mirzayans, E.A. Siegbahn , B.G. Fallone and B. Warkentin,
"Comparison of two methods for measuring γ-H2AX nuclear fluorescence as a marker of DNA damage in cultured human cells: applications for microbeam radiation therapy,
Journal of Instrumentation, 8(6), C06008- (2013).

S Steciw, S Rathee, B Warkentin,
"Modulation factors calculated with an EPID-derived MLC fluence model to streamline IMRT/VMAT second checks"
Journal of Applied Clinical Medical Physics. 14(6), 62-81 (2013).

B. Warkentin, S Rathee, S. Steciw,
"2D Lag and signal non-linearity correction in an aS500 EPID and their impact on pretreatment dosimetric verification"
Med. Phys. 39(11), 6597-6608 (2012).

A. Keyvanloo, B. Burke, B. Warkentin, T. Tadic, S. Rathee, C. Kirkby, D.M. Santos, B.G. Fallone,
"Skin dose in longitudinal and transverse linac-MRIs using Monte Carlo and realistic 3D MRI field models."
Med Phys (10), 6509-6521 (2012).

D. Anderson, E.A. Siegbahn, B.G. Fallone, R. Serduc, B. Warkentin,
"Evaluation of dose-volume metrics for microbeam radiation therapy dose distributions in head phantoms of various sizes using Monte Carlo simulations."
Phys Med Bio 57(10), 3223-48 (2012).

P. Stavrev, C. Schinkel, N. Stavreva, B. Warkentin, M. Carlone, B.G. Fallone,
"Population TCP estimators in case of heterogeneous irradiation: A new discussion of an old problem,"
Act Oncol, 49(8), pp. 1293-1303 (2010).

C. Schinkel, M. Carlone, B. Warkentin and B.G. Fallone,
"An analytic investigation into the effect of population heterogeneity on parameter ratio estimates."
Int J Radiat Oncol Biol Phys. 2007 Nov;69(4):1323-30

M. Carlone, B. Warkentin, P. Stavrev and B.G. Fallone,
"Fundamental form of the population TCP model in the limit of large heterogeneity."
Med. Phys. 33(6), pp. 1634-1642, 2006.

S. Steciw, B. Warkentin, S. Rathee and B.G. Fallone,
"Three dimensional IMRT verification with a flat-panel EPID."
Medical Physics, Vol. 32, No. 2, pp. 600-612, 2005.

B. Warkentin, P. Stavrev, N.A. Stavreva and B.G. Fallone,
"Limitations of a TCP Model Incorporating Population Heterogeneity"
Physics in Medicine and Biology 50(15), pp. 3571-88, 2005.

N.A. Stavreva, B. Warkentin, P.V. Stavrev and B.G. Fallone,
"Investigating the Effect of Clonogen Resensitization on the Tumor Response to Fractionated External Radiotherapy."
Medical Physics 32(3), pp. 720-25, 2005.

P. Stavrev, M. Weldon, B. Warkentin, N.A. Stavreva and B.G. Fallone,
"Radiation Damage, Repopulation and Cell Recovery Analysis of In Vitro Tumour Cell Megacolony Culture Data Using a Non-Poissonian Cell Repopulation TCP Model."
Physics in Medicine and Biology 50(13), pp. 3053-61, 2005.

B. Warkentin, P. Stavrev, N. Staverva, G.C. Field and B.G. Fallone,
"A TCP-NTCP estimation module using DVHs and known radiobiological models and parameter sets."
J. App. Clin. Med. Phys, 5(1), pp. 50-63, 2004.

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