MRI-guided transurethral ultrasound therapy enables full prostate gland coagulation: Investigations in gel phantoms

MRI-guided transurethral ultrasound therapy has previously been evaluated in human volunteers by treating a prostate subvolume, prior to radical prostatectomy. Extension of this technique to full clinical use requires validation of the technique for coagulating a volume of tissue equivalent to the entire gland. This in-vitro study evaluates approaches for treating the whole prostate gland by comparing various treatment strategies. An 8-element ultrasound therapy system was evaluated in gel phantoms using 6 human prostate profiles segmented from MR clinical images (average volume: 36 cm3). Real-time MR-thermometry feedback was performed over nine slices covering the entire prostate. Decisions on acoustic power, frequency, and device rotation rate were made based on prostate target radii and temperature maps updated every 7s. Low and high power treatment approaches (10, 20 W/cm2) were tested as well as single-and dual-frequency strategies (8.1, 4.6/14.4 MHz). Decreasing frequency to 4.6 MHz enabled treating 97% of the gland on average. A 20/10 W/cm2 dual-frequency 4.6/14.4 MHz treatment was the most efficient configuration in achieving full human prostate treatments. Treatments were performed more quickly (<30min) with enhanced treatment safety close to the base and apex. Transurethral thermal therapy has been validated in vitro for full gland treatment in human prostate geometries.