MRI-guided transurethral ultrasound therapy of the prostate gland: simulations under clinical conditions

Abstract

The feasibility of performing MRI‐guided transurethral ultrasound therapy in humans has been shown by our group for the treatment of small subvolumes prior to radical prostatectomy. One challenge is to use this technology to treat a volume of tissue equivalent to the entire prostate gland. This simulation study evaluates the feasibility of treating the whole prostate gland and characterizes the nature of the treatment with respect to treatment time, accuracy, and safety. A numerical model was used to simulate a multi‐element heating applicator rotating inside the urethra in five human prostates. 3D prostate profiles were segmented from clinical MR images obtained from subjects after insertion of a transurethral heating applicator into the prostate gland. Clinical treatment planning conditions were simulated including device orientation, prostate & rectum geometry, temperature uncertainty, imaging time, and spatial resolution. During ultrasound exposures, acoustic power, frequency and rotation rate were varied based on the prostate radius and on temperature feedback every 5 seconds using MR thermometry. Two treatment approaches (10 or 20 W.cm−2 acoustic power) were tested as well as single and dual‐frequency strategies (4.05/13.10 MHz). A 20 W.cm−2 dual‐frequency treatment was shown to be the most efficient configuration in achieving full human prostate treatments. Increasing the power from 10 to 20 W.cm−2 led, on average, to treatment times shorter by 50%. Full prostate coagulations were performed in 20.6±1.6 min at a rate of 1.6±0.2 cm3.min−1, and resulted in <8% of undertreated tissue. This configuration succeeded in preserving high‐priority critical regions such as the adjacent rectal wall tissues. The principles of prostate thermal therapy using an MR thermometry‐guided transurethral ultrasound technique were shown in simulations to be suitable for full gland treatment in prostate geometries derived from human subjects undergoing partial coagulations. Dual‐frequency 20 W.cm−2 ultrasound exposures offer a promising configuration for future clinical investigations of full prostate treatments.