MRI-controlled transurethral ultrasound therapy for localised prostate cancer

Minimally invasive treatments for localised prostate cancer are being developed with the aim of achieving effective disease control with low morbidity. High-temperature thermal therapy aimed at producing irreversible thermal coagulation of the prostate gland is attractive because of the rapid onset of thermal injury, and the immediate visualisation of tissue response using medical imaging. High-intensity ultrasound therapy has been shown to be an effective means of achieving thermal coagulation of prostate tissue using minimally invasive devices inserted into the rectum, urethra, or directly into the gland itself. The focus of this review is to describe the work done in our group on the development of MRI-controlled transurethral ultrasound therapy. This technology utilises high intensity ultrasound energy delivered from a transurethral device to achieve thermal coagulation of prostate tissue. Control over the spatial pattern of thermal damage is achieved through closed-loop temperature feedback using quantitative MR thermometry during treatment. The technology, temperature feedback algorithms, and results from numerical modelling, along with experimental results obtained in animal and human studies are described. Our experience suggests that this form of treatment is technically feasible, and compatible with existing MR imaging systems. Temperature feedback control algorithms using MR thermometry can achieve spatial treatment accuracy of a few millimetres in vivo. Patient-specific simulations predict that surrounding tissues can be spared from thermal damage if appropriate measures are taken into account during treatment planning. Recent human experience has been encouraging and motivates further evaluation of this technology as a potential treatment for localised prostate cancer.