The ELASTO-US study is a single center feasibility study to evaluate 3 methods of analyzing real-time ultrasound images acquired during High Intensity Focused Ultrasound (HIFU) treatment in patients with localized prostate cancer.

Real-time ultrasound acquisitions will be programmed at specific times and recorded during HIFU treatment. At the end of the treatment, these recordings will be exported in an anonymized way and analyzed according to the 3 different methods.

A multiparametric-MRI will be performed in addition to the usual practice within 5 days after the treatment in order to control the area necroticised by the treatment. The mp-MRI will be the reference method against which the results obtained by the 3 methods of ultrasound image analysis will be compared.

Techniques capable of providing safe and robust information on the progress of HIFU-generated necrosis would greatly limit the risks of overtreatment that can lead to side effects such as urinary incontinence as well as the risks of under treatment that can lead to cancer recurrence.

Inclusion Criteria:

• Patient who has been clearly informed of the study and has agreed, with sufficient time for reflection, to participate by signing the study informed consent form.
• Male aged ≥ 50 years,
• PSA ≤ 15 ng/mL
• diagnosis of localized prostate cancer (stage T1 or T2) with a Gleason score of ≤ 7
• Focal, hemiablation or ablation HIFU treatment validated in Multidisciplinary Concerted Meeting
• Patient enrolled in Medicare or equivalent plan.
• Interpretable preoperative multiparametric MRI performed within 180 days prior to surgery

Exclusion Criteria:

• an ASA score >3
• brachytherapy for prostate cancer
• Person of full age protected by law (person under guardianship or curatorship).
• Contraindication to HIFU treatment as defined in the Focal One instructions for use : - Multiple intraprostatic calcifications inducing, on ultrasound, a shadow cone in the prostate preventing the penetration of ultrasound and therefore the realization of the treatment.
• Presence of permanent radioactive implants in the rectal wall.
• Presence of an implant (stent, catheter) located less than 1 cm from the treatment area.
• Fistula of the urinary tract or rectum.
• Anal or rectal fibrosis, anal or rectal stenosis or other abnormalities making insertion of the Focal One® catheter difficult.
• Anatomical abnormality of the rectum or rectal mucosa.
• Patient with an artificial sphincter, penile prosthesis or intraprostatic implant, such as a stent.
• History of inflammatory bowel disease.
• Current urogenital infection (infection should be treated prior to HIFU treatment).
• Patient allergic to latex with known severe reactionsCounter-indications to anesthesia