Evaluation of Focal Ablation of Magnetic Resonance Imaging Defined Prostate Cancer Using Magnetic Resonance Imaging Controlled Transurethral Ultrasound Therapy with Prostatectomy as the Reference Standard

Abstract

Purpose: We evaluated magnetic resonance imaging controlled transurethral ultrasound therapy as a treatment for magnetic resonance imaging defined focal prostate cancer using subsequent prostatectomy and histology as the reference standard.

Materials and methods: Five men completed this pilot study, which was approved by the institutional review board. Prior to radical prostatectomy focal tumors identified by magnetic resonance imaging were treated by coagulating targeted subtotal 3-dimensional volumes of prostate tissue using magnetic resonance imaging controlled transurethral focused ultrasound. Treatment was performed with a 3 Tesla clinical magnetic resonance imaging unit combined with modified clinical planning software for high intensity focused ultrasound therapy. After prostatectomy whole mount histological sections parallel to the magnetic resonance imaging treatment planes were used to compare magnetic resonance imaging measurements with thermal damage at the cellular level and, thus, evaluate treatment and target accuracy.

Results: Three-dimensional target volumes of 4 to 20 cc and with radii up to 35 mm from the urethra were treated successfully. Mean ± SD temperature control accuracy at the target boundary was -1.6 ± 4.8C and the mean spatial targeting accuracy achieved was -1.5 ± 2.8 mm. Mean treatment accuracy with respect to histology was -0.4 ± 1.7 mm with all index tumors falling inside the histological outer limit of thermal injury.

Conclusions: Magnetic resonance imaging guided transurethral ultrasound therapy is capable of generating thermal coagulation and tumor destruction in targeted 3-dimensional angular sectors out to the prostate capsule for prostate glands up to 70 cc in volume. Ultrasound parameters needed to achieve ablation at the prostate capsule were determined, providing a foundation for future studies.

Keywords: high-intensity focused ultrasound ablation; magnetic resonance imaging; minimally invasive surgical procedures; prostatic neoplasms; transurethral resection of prostate.

Copyright © 2017 American Urological Association Education and Research, Inc. Published by Elsevier Inc. All rights reserved.

Figures

FIG. 1

a) Photograph of the ultrasound applicator (UA). b) Photograph of the endorectal cooling device (ECD). The flow of cooling water is in the direction of the black arrow, while the red dotted line indicates a thin plastic window placed in the vicinity of the prostate gland. c) MR image showing the UA placed within the urethra in the prostate (Pr) with its tip in the bladder (Bl), and the ECD in the rectum with its plastic window (red arrow) oriented toward the prostate.

FIG. 2

Panels a, b and c show axial, coronal and sagittal images reformatted from a T2w 3D TSE data set. The transducer elements are represented as orange diamonds. Two markers (indicated by thick white arrows) were aligned with applicator features as seen in the MR images to register the device with the planning software. A planned treatment sector is shown in yellow. Panel d shows a sagittal view with the transducer and ECD inserted. The dashed white box indicates the plane of image c, while the perpendicular lines indicate the planes of the images in panels a and b. Pr=prostate, Bl=Bladder, ECD=endorectal cooling device.

FIG. 3

A collage of the axial maximum temperature maps at the end of treatment for all slices of all five completed cases in the study. Superimposed on each image are the 240EM dose line (white) and the boundaries of the treatment sector (blue). In the final slice of P1, the transducer element failed during treatment, resulting in insufficient heating in that location (white arrow).

FIG. 4

Histology images for all 6 slices of the treatment of Patient 6. Each image shows the prostate boundary (blue), the tumour boundary (yellow), the acute coagulative necrosis boundary (white) and the outer limit of thermal damage (black). Between the latter two boundaries, cells may not be immediately destroyed by the treatment, but are likely to undergo delayed necrosis. The scale bars indicate 2 mm.