Can focused ultrasound replace watchful waiting for prostate cancer?

Copied word for word from the study's registry entry, so the wording is the study team's rather than ours.

Inclusion Criteria: * Patient having been clearly informed of the study and having accepted, with sufficient reflection time, to participate by signing the informed consent form of the study. * Age between 50 and 80 years with a life expectancy of more than 5 years. Patients between the ages of 75 and 80 will need to have G8 score \> 14. * Initial diagnosis of localized prostate cancer (T1c or T2a) with the following characteristics: * Only one Target tumor on MRI on a maximum of 2 contigous sextants. Case allowed: * If more than one target tumor on MRI, only one of them must be confirmed by targeted prostate biopsies. * If no target tumor on MRI, only 2 contigous sextants must be positive on prostate biopsies * A maximum tumor length\> 3 mm or at least 3 positive biopsies on all biopsies performed (randomized biopsies and/or MRI/Ultrasound Fusion-Guided Prostate Biopsy). * Gleason 6 score (risk group 1 of the D'Amico classification). * Tumor positioned so that a safety distance of at least 9 mm from external sphincter can be defined during HIFU-FOCAL treatment in prostate tissue around the target. * PSA ≤ 15ng / ml. * Patient affiliated with health insurance or beneficiary of an equivalent plan. Exclusion Criteria: * Contraindications to treatment with HIFU-F: * Tumor not accessible. * Multiple intra prostatic calcifications inducing, on ultrasound, a shadow cone in the prostate preventing the penetration of ultrasound and thus the realization of the treatment. * History of pelvic irradiation * 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 it difficult to insert the Focal One® probe. * Anatomical abnormality of the rectum or rectal mucosa. * Patient with artificial sphincter, penile prosthesis or intra prostatic implant, eg stent. * History of intestinal inflammatory pathology. * Uro-genital infection in progress (the infection to be treated before HIFU treatment). * Anterior surgery at the level of the anus or rectum making the introduction of the probe impossible. * Allergy to latex. * Thickness of the rectal wall\> 10mm. * TURP indication. Bladder neck incision is allowed . * Patient with a medical contraindication to Sonovue® injection. * Patient with a medical contraindication on MRI. * Patient already treated for prostate cancer (hormone therapy, radiotherapy, surgery). * History of uncontrolled cancer and / or treated for less than 5 years (with the exception of basal cell skin cancer). * History of sclerosis of the bladder neck or urethral stenosis. * Patient with a several bleeding risk according to medical advice (patient with oral anticoagulant therapy must receive an alternative therapy if randomized in HIFU-F arm). * Patients with unstable neurological pathology. * Patient who has been treated for a therapeutic trial within 30 days of enrollment or who wishes to participate in an ongoing study that may interfere with this study. * Legal person protected by law. * Patient not able to understand the objectives of the study or refusing to comply with postoperative instructions.