Sunnybrook Health Sciences Centre, Toronto, Ontario, Canada

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					Initial human evaluation of MRI-guided transurethral ultrasound therapy for the
treatment of localized prostate cancer
              1,2                         1,2                 1,2                   1,2
Rajiv Chopra , Alexandra Colquhoun , Kashif Siddiqui , Masoom Haider , Michael
         1,2              1,2
Bronskill , Laurence Klotz
1                                                                       2
 Sunnybrook Health Sciences Centre, Toronto, Ontario, Canada, University of Toronto,
Toronto, Ontario, Canada

INTRODUCTION: Minimally-invasive treatments for localized prostate cancer that provide
local control with a low side-effect profile would have a major impact in improving disease
management. MRI-guided transurethral ultrasound therapy is such a technology in which
high-intensity ultrasound energy from a device inserted into the prostatic urethra generates an
accurate region of thermal coagulation in the gland. Previous studies in gels and canines
have demonstrated the spatial accuracy achieved using active MR temperature feedback to
control the heating of a target region in the gland. The purpose of this study was to evaluate
the safety and feasibility of this approach in human prostate gland in a pilot human study.

METHODS: MRI-guided transurethral ultrasound therapy was used to treat a subvolume of
the prostate gland in men diagnosed with localized prostate cancer. Subjects underwent a
radical prostatectomy shortly after the procedure, and the pattern of thermal damage
measured on histology was compared with imaging measurements during and post-
treatment. The procedure was performed in a 1.5T closed-bore MRI and each subject was
administered a spinal anaesthetic prior to treatment to eliminate sensation in the pelvis and
reduce motion. High-intensity ultrasound energy was delivered to a 180° sector in the
prostate, and spatial temperature maps were obtained every five seconds using the PRF shift
method. The temperature measured at the boundary of the target region during treatment was
used by the treatment system to adjust the power and rotation rate

RESULTS: Five patients have been treated to date. The transurethral device was
successfully inserted into patients in the supine imaging position, and the setup fit comfortably
within the bore of the MR imager. The spinal anaesthetic eliminated patient discomfort and
motion during the procedure, which lasted for a total of 2 hours. Precise positioning of the
transducer within the prostate gland was achieved under image-guidance, and the device was
successfully rotated within the prostate gland. MR temperature maps were obtained every 5
seconds with a spatial resolution of 2mm (in-plane) and a temperature uncertainty of
approximately 1°C using a conventional pelvic surface-coil array. The temperature
measurements were stable, and not significantly affected by motion or breathing. A
continuous pattern of heating was delivered over the target region, and the targeting accuracy
was approximately 1.0 ± 1.5 mm.

CONCLUSIONS: MRI-guided transurethral ultrasound therapy is capable of generating a
precise region of thermal damage within the human prostate gland under active MR
temperature feedback.