Clinical validation of real-time tissue change monitoring during prostate tissue ablation with high intensity focused ultrasound

BACKGROUND: The purpose of these clinical studies was to validate a Tissue Change Monitoring (TCM) algorithm in vivo. TCM is a quantitative tool for the real-time assessment of HIFU dose. TCM provides quantitative analysis of the backscatter pulse echo signals (pre and immediately post HIFU) for each individual ablative site, using ultrasonic tissue characterization as a surrogate for monitoring tissue temperature. Real-time analysis generates an energy difference parameter (ΔE in dB) that is proportional to tissue temperature. METHODS: Post in vitro studies, two clinical studies were conducted to validate the TCM algorithm on the Sonablate® device. Studies enrolled histologically confirmed, organ confined prostate cancer patients. The first clinical study was conducted in two phases for whole gland ablation. First eight patients’ data were used to measure the algorithm performance followed by 89 additional patients for long term outcome. The second clinical study enrolled five patients; four patients with focal cancer had hemi-ablation only and one had whole gland ablation. Four 3 Fr. needles containing three thermocouples each were placed transperineally in the prostate to record tissue temperatures in the focal zone, posterior to the focal zone and on the lateral gland where no HIFU was applied. Tissue temperatures from the focal zone were correlated to the ΔE parameter. RESULTS: In the first clinical study, the average TCM rate was 86%. Pre and 6 months post HIFU, median PSA was 7.64 and 0.025 ng/ml respectively and 97% patients had negative biopsy. For the second clinical study, the measured prostate tissue temperatures (Average, Max, and Min) in the ablation zones were 84°, 114° and 60 °C and the corresponding ΔE (dB/10) parameters were 1.05, 2.6 and 0.4 resulting in 83% of temperatures in the range of 75°-100 °C and 17% in the 60°-74 °C range. Outside the focal zone, the average temperature was 50 °C and in the lateral lobe where no HIFU was applied, peak temperature was 40.7 °C. CONCLUSIONS: The TCM algorithm is able to estimate tissue changes reliably during the HIFU procedure for prostate tissue ablation in real-time and can be used as a guide for HIFU dose delivery and tissue ablation control.