Theoretical analysis of the accuracy and safety of MRI-guided transurethral 3-D conformal ultrasound prostate therapy

MRI-guided transurethral ultrasound therapy is a promising new approach for the treatment of localized prostate cancer. Several studies have demonstrated the feasibility of producing large regions of thermal coagulation adequate for prostate therapy; however, the quantitative assessment of shaping these regions to complex 3-D human prostate geometries has not been fully explored. This study used numerical simulations and twenty manually-segmented pelvic anatomical models derived from high-quality MR images of prostate cancer patients to evaluate the treatment accuracy and safety of 3-D conformal MRI-guided transurethral ultrasound therapy. The simulations incorporated a rotating multi-element planar dualfrequency ultrasound transducer (seventeen 4×3 mm elements) operating at 4.7/9.7 MHz and 10 W/cm² maximum acoustic power. Results using a novel feedback control algorithm which modulated the ultrasound frequency, power and device rate of rotation showed that regions of thermal coagulation could be shaped to predefined prostate volumes within 1.0 mm across the vast majority of these glands. Treatment times were typically 30 min and remained below 60 min for large 60 cc prostates. With a rectal cooling temperature of 15°C, the rectal wall did not exceed 30EM43 in half of the twenty patient models with only a few 1 mm³ voxels above this threshold in the other cases. At 4.7 MHz, heating of the pelvic bone can become significant when it is located less than 10 mm from the prostate. Numerical simulations show that MRIguided transurethral ultrasound therapy can thermally coagulate whole prostate glands accurately and safely in 3-D.