Assessment of HIFU-induced Prostate Necrosis With Shear-wave Ultrasound Elastography

Transrectal High-intensity Focused Ultrasound (HIFU) is a minimally-invasive therapy for prostate cancer that is currently assessed in two indications: as a first-line treatment (either total or focal) for patients who are not eligible for surgery and as a salvage treatment of local recurrences after radiotherapy. It has recently been shown that Contrast-Enhanced Ultrasound (CEUS) can accurately assess the position and volume of tissue destruction at the end of prostate HIFU ablation. This can provide live feedback regarding the amount of residual non ablated tissue after HIFU treatment, which could allow immediate re-treatment in case of unsatisfactory result. CEUS requires the injection of micro-bubbles of sulphur hexafluoride (Sonovue, Bracco, Milan, Italy) which can, at least in theory, interfere with HIFU treatment. Therefore, it is necessary to wait 20 to 30 minutes before re-treating the patient. Shear-wave ultrasound elastography (SWUE, Supersonic Imagine, Aix-en-Provence, France) can quantify tissue stiffness. Moreover, post-HIFU necrosis is known to be stiffer than undestroyed prostate tissue. Therefore, SWUE could be an alternative to CEUS, and the purpose of this study is to evaluate the accuracy of SWUE in depicting the position and volume of therapeutic necrosis after prostate cancer High-Intensity Focused Ultrasound (HIFU) ablation. The present study is an exploratory, monocentric, prospective, descriptive study. Three groups of 10 patients with prostate cancer will be evaluated: patients referred for first-line prostate HIFU ablation, patients referred for first-line HIFU hemi-ablation (focal treatment) and patients referred for salvage HIFU after radiotherapy. SWUE will be obtained the day before HIFU ablation (D-1), immediately after HIFU ablation (D0) and the following day (D+1). CEUS will be performed immediately after HIFU ablation and D0 SWUE. The primary endpoint is the comparison of the thickness of undestroyed parenchyma measured by SW