Magnetic resonance image guided transurethral ultrasound prostate ablation: a preclinical safety and feasibility study with 28-day followup.

PURPOSE We determine the safety and feasibility of magnetic resonance image guided transurethral ultrasound prostate ablation using active temperature feedback control in a preclinical canine model with 28-day followup. MATERIALS AND METHODS After a long acclimatization period we performed ultrasound treatment in 8 subjects using the magnetic resonance image guided TULSA-PRO™ transurethral ultrasound prostate ablation system. Comprehensive examinations and observations were done before and throughout the 28-day followup, including assessment of clinically significant treatment related adverse events. In addition to gross pathology evaluation, extensive histopathological analysis was done to assess cell kill inside and outside the prostate. We evaluated prostate conformal heating by comparing the spatial difference between the treatment plan and the 55C isotherm measured on magnetic resonance imaging thermometry acquired during treatment. These findings were confirmed on contrast enhanced magnetic resonance imaging immediately after treatment and at 28 days. RESULTS Clinically there were no adverse events in any of the 8 subjects throughout the 28-day followup. All subjects had normal urinary and bowel function. Gross necropsy and histology confirmed that the intended thermal cell kill was confined to the prostate. No surrounding tissue was damaged, including the rectum and the external urinary sphincter. Conformal heating was achieved with an average -0.9 mm accuracy and 0.9 mm precision. Contrast enhanced magnetic resonance imaging and histological analysis confirmed tissue ablation in targeted areas of the prostate. Urethral tissue was spared from thermal damage. CONCLUSIONS Magnetic resonance image guided transurethral ultrasound is a safe, feasible procedure for accurate and precise conformal thermal ablation of prostate tissue, as demonstrated in a preclinical model with 28-day followup.