Fall 2011 - Institute of Medical Science - University of Toronto

FEATURE
Imaging and Prostate Cancer
Applications of MRI
Dr. Masoom Haider
MD, FRCPC
Clinician Scientist, Ontario Institute for
Cancer Research
Associate Member, Institute of Medical
Science
Associate Professor of Radiology, University
of Toronto, Faculty of Medicine, Department
of Medical Imaging
One of the primary goals of current
cancer research is to develop
patient-specific personalized therapeutic
approaches that maximize treatment
efficacy while minimizing morbidity. In the
current era of serum prostate specific antigen
(PSA) screening for prostate cancer, detection
is occurring at an earlier stage; however,
prostate cancer has a highly variable natural
history and in many cases the cancer will remain
indolent throughout the patient’s lifetime.
There is a consensus that in the PSA
screening era prostate cancer is being overtreated
1 .
There is a wide array of options for therapy
including active surveillance (see page 21),
prostatectomy (laproscopic, robotic, retropubic),
hormonal therapy, and radiation
therapy (external beam, intensity modulated
radiation therapy, brachytherapy). Selection
of the appropriate treatment is based on risk
stratification. The primary method for risk
stratification hinges on obtaining tissue using
a random prostate biopsy of the gland
guided by transrectal ultrasound (TRUS)
consisting of at least 8 needle cores. Using the
histologic Gleason grade of the tissue sample,
the PSA, and the result of digital rectal exam,
the patient is placed in a risk category and
this helps guide management choices. This
approach suffers from two shortcomings.
The first is the sampling problem. TRUS biopsy
even with 10 cores is not representative
of the tumor grade at prostatectomy in about
30% of cases and thus the patient’s risk category
can be misclassified 2 . Secondly, the risk
stratification currently used is predictive but
when applied on a patient-by-patient basis
does not always reliably predict an individual
patient’s long-term outcome. Furthermore,
prostate biopsy is painful and caries a small
but significant risk of urosepsis 3 , while whole
gland therapies carry the risk of sexual dysfunction
and urinary continence problems 4 .
Thus, finding a non-invasive biomarker of
outcome in prostate cancer is one of the principal
aims of current research.
In recent years, of all imaging methods available
for clinical use, MRI has shown the
greatest promise of addressing these issues in
the short term. In particular the use of multiparametric
MRI, which combines two or
more MRI acquisitions such as T2 weighted
imaging, diffusion weighted imaging, dynamic
contrast enhanced imaging or proton
spectroscopy, has been successful in localizing
prostate cancer for directed biopsy 5-8 and
shown promise in predicting Gleason grade
without the need for biopsy 9, 10 . There remain
shortcomings. Much of the data supporting
the MRI approach comes from single center
trials, and there are too few prospective trials
showing improved survival. Training of radiologists
is lacking and MRI availability is limited,
although this is expected to change as
standards develop and evidence of improvements
in patient outcome is published over
the next few years. A prospective multicenter
trial is underway in select centers – including
our group, funded by the Ontario Institute
of Cancer Research – to evaluate MRI use
with specific treatments such as active surveillance
to see if patients can be better se-
Photo by Paulina Rzeczkowska
19 | IMS MAGAZINE FALL 2011 PROSTATE CANCER