Phase 3, Multicenter, Randomized Study, Evaluating the Efficacy and Tolerability of Focused HIFU (High Intensity Focused Ultrasound) Therapy Compared to Active Surveillance in Patients With Significant Low Risk Prostate Cancer

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.