Page 7 - Eureka! Spring 2007

Research news the physical body The shape Research news

of things to come
physics to make the treatment of cancer more precise.
pplying physics to problems of human health has
Members of the Ottawa Medical Physics Institute (OMPI),
Aresulted in the invention of the computed tomographic
an organized research unit of the Department of Physics,
(ct) scanner, the use of high-energy photon and electron
they are part of a dynamic network of 30 medical physi-
beams for cancer therapy, and the development of the
magnetic resonance (MR) imager. Medical physics holds
cists—at health canada, the National Research council,
veryone knows their height, and most
promise for improvements in the diagnosis and understand-
dimensions, so I’m trying to find ways to
ing of disease and for patient care.
centre, Nucletron canada, and carleton University—col-
make those techniques run efficiently
these two numbers tell us about our
carleton’s Dr. David Rogers and Dr. tong Xu are using the Ottawa heart Institute, the Ottawa hospital and cancer E of us know our weight, but what do to explore volumes of data in multiple
laborating on common research and academic matters.
health? Plunk that data into the algorithm on the computer.”
for the body mass index (divide weight Because the statistics have more than
calculating a cure in kilograms by height in meters squared one dimension, they become geometric
Brachytherapy seems straightforward: exposure to other areas.” “Brachytherapy is easier for the and multiply by 100) to determine how problems. Instead of the statistician’s usual
place a radioactive source inside or The commercial treatment planning protate patient than other forms of much your weight departs from what is distribution patterns, the recent concept of
next to a tumour in the prostate or system in use by medical physicists radiation,” says Rogers. “There are normal for a person of that height, and statistical data depth offers a new perspec-
breast to kill it. But like all cancer to calculate dose has the advantage of still other uncertainties that knowing the hidden relationship between height tive: a centre-outward ordering of points in
treatments, finding the dose that will speed, at the expense of accuracy. Rog- the dose won’t resolve, but people are and weight is revealed in a simple chart Euclidean space of any dimension. Morin’s
kill cancer with minimal harm to the ers’ code is so fast that it can calculate eager for ways to make the treatment with bands of “underweight”, “normal” algorithms will exploit geometry, looking
patient is tricky. The complex inter- in three minutes what other codes take process faster and more accurate.” and “obese” running along two axes. for shapes that contain the most points or
actions inside a human body, and six hours to do—and it is within two But what if you want a better picture separating them into classes.
variables such as body fat and the per cent statistical accuracy. Sighting a moving target of the risk of heart disease? what kind of “this is such a big area, I could study
location of the tumour, make precise Using random numbers, knowledge How do you hit a moving target? For Tong Xu’s PeTrack system can be applied to chart is produced if age, sex, blood pres- it for the rest of my career, but I can’t do
real-time tool tracking for surgery as well as to tu-
dose delivery a Herculean task. of the probability of various interac- pulmonary and abdominal cancers, mours. By embedding a positron emission marker sure and waist measurement are added? it all myself,” says Morin, who has been
That’s why David Rogers, Canada tions, information from CT scans and the very act of breathing makes it in tools or coating tool surfaces, their position in how are relationships between so many studying this area on and off for five years.
Research Chair in Medical Physics and the initial amount of radioactivity, difficult to deliver radiotherapy ac- the patient can be tracked. dimensions discovered? he plans to hire a post-doctoral fellow with
head of the Carleton Laboratory for the Monte Carlo simulation predicts curately as the tumour moves with Enter Dr. Patrick Morin, computa- the carty Fellowship funding to help move
Radiotherapy Physics, is developing a where the energy is deposited. Run- each breath. PeTrack was accurate within less tional geometer. the research forward. “we’ll be able to
faster Monte Carlo code —an algorithm ning the simulation repeatedly Tong Xu, Assistant Professor in than a millimeter. Using a positron contribute more and expand the breadth of
using random numbers—for more ac- removes randomness and averages the the Department of Physics, is de- emission tomography detector at the the research project.”
curate dose calculations. behaviour, resulting in an accurate veloping real-time tumour tracking Ottawa Heart Institute, Xu’s experi- carleton established the carty Research
“By understanding the physics of and fast code. for radiation therapy using positron mental results showed .3 to .6 mil- Fellowship program in 2006 to provide
photon interaction in the body—the Rogers’ team is running final checks emission isotopes. limeter accuracy with one stationary seed funding for new faculty members to
angle it bounces, when it creates an and benchmarking the code against “We’ve reached a bottleneck in marker. The next step is to add mo- initiate innovative research and scholarly
energetic electron—we can simulate a other forms of dose calculation, with treatment accuracy, so now we need tion and multiple markers so that the activities. the program was founded with
photon’s movement billions of times the goal of releasing the calculation to accuracy in tumour tracking,” says location and shape of a tumour can $4 million from the endowment left by
over to see what it will do,” says Rog- collaborators at research clinics this Xu. “By tracking a tumour’s exact be tracked in three dimensions. former public servant and philanthropist E.
ers. “Knowing where the radiation goes summer or fall. With feedback from position, the radiotherapy x-ray beam “The challenge with multiple Bower carty. Morin was among nine faculty
helps doctors to better position the ra- the laboratory, Rogers hopes to make could move with it, reducing treat- markers is to keep the necessary members awarded the inaugural fellow-
dioactive seeds in the body to deliver a the code user friendly before releasing ment time and reducing the exposure algorithm fast,” says Xu, whose ships. Morin has also received funding
uniform dose and to minimize it for general use in 2008. of healthy tissue to radiation.” algorithm currently can locate four from the Ontario Innovation trust and the
Current tracking methods involve static markers in 20 milliseconds. canada Foundation for Innovation New
exposing healthy tissue to x-rays that He expects to have the first PeTrack Opportunities Fund.
pick up markers implanted in the tu- prototype ready in two years for “I’m very lucky to be working with the
mour, or using large electromagnetic animal trials, with patient trials fol- Pat Morin is the first professor in the Faculty world-class computational geometry group
transponders that can cause a lung lowing a year later. of Science to receive funding from the Carty here at carleton. the carty Fellowship is a
to collapse or leak air when they Research Fellowship program. great boost for this project,” he says.
are inserted. !
Xu’s technique, called PeTrack, uses Fast fact... Morin, Bcs/96, Mcs/98, PhD/01,
positron emission isotopes, housed Established in 2004, the Robert L. Clarke an Associate Professor in the school of
in small markers less than 0.8 mil- Graduate Scholarship in Medical Physics computer science, received an inaugural
limeters in diameter. Inserted into is awarded annually to an outstanding carty Research Fellowship from carleton ! Fast fact...
the tumour, the emitted positron, student specializing in Medical Physics. University to study more efficient meth-
on meeting an electron, gives out a This award was developed to recognize ods for computing statistics on data with Carleton’s School of Computer Science
gamma ray that is picked up by de- the contribution of the late Dr. Robert more than one dimension. is hosting the 2007 Canadian Conference
tectors positioned on each side of Clarke, Distinguished Research Professor “statisticians work on techniques on Computational Geometry from August
20 to 22. The annual international event,
and founder of the Ottawa Medical
the body. Multiple gamma rays allow Physics Institute. To learn more, or for discovering relationships between which attracts students and researchers
for the position of the marker to to contribute to the Robert L. Clarke data, but some of these techniques are alike, disseminates new results in the
David Rogers used funds from the Canadian Foundation for Innovation to purchase 60 computers on be calculated. Scholarship in Medical Physics, see not very computationally feasible,” says fields of computational and combinatorial
which to run his calculations. When the medical physicists aren’t using them, they are available to the In initial computer simulations, carleton.ca/science/events/Clarke. Morin. “computers offer a mechanism geometry. Visit 2007.cccg.ca for details.
particle physicists to maximize their benefit to the department’s research.

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