Stereo-Re-Pro aims to provide further evidence of Stereotactic Body Radiotherapy (SBRT) as a supplementary non-invasive curative treatment for local recurrence following radiotherapy.

The objective of the first part of the trial (Phase I) is to select the recommended dose for salvage SBRT (either 5 x 6 Gy, 6 x 6 Gy, or 5 x 5 Gy) based on dose-limiting toxicity observed during the 18 weeks following the initiation of salvage-SBRT. Particular attention will be paid to the quality of life and tolerance of the treatment.

The objective of the second part of the trial (phase II) is to estimate the efficacy of the salvage-SBRT in terms of biochemical relapse-free survival rate.

To date, no standard local treatment exists for patients with an intraprostatic recurrence after radiotherapy. A number of treatments options exist including: radical prostatectomy, brachytherapy, High-intensity focused ultrasound (HIFU), cryotherapy, and stereotactic radiotherapy. These treatments are associated with a variety of genitourinary and gastrointestinal toxicities and complications. In recent years, stereotactic radiotherapy has been used to treat localized prostate cancer in the primary setting but also as a salvage treatment after failure of radiotherapy. The initial results of these studies are promising, with respect to survival and tolerance, but further studies are required to confirm these initial results.

The objective of STEREO-RE-PRO is to prospectively evaluate salvage SBRT for intraprostatic recurrent prostate cancer after primary external radiotherapy. This study will select patients for whom there is no standard local treatment.

After inclusion and non-inclusion criteria have been verified and the patient has consented, the site will register the screening and organize the baseline visit with the placement of fiducial markers within two months before the planned start of SBRT.

Once the fiducial placement has been performed and all eligibility criteria fully reviewed, the site will register the patient's participation so that the bio-statistician allocates the dose of SBRT. The dose will be allocated upon a model-based estimates provided by the statistical team and confirmed by the trial steering committee. Five or six fractions, at a level of 5 or 6 Gy per session (either 5 x 6 Gy, 6 x 6 Gy, or 5 x 5 Gy), will be delivered over a maximum of 12 days to provide a total dose of 25 to 36 Gy. During the treatment phase of the study, no study specific visits are scheduled and the patients will be followed as per standard of care.

A follow-up visit is planned at 6, 10, 18 weeks from the start of SBRT for safety evaluation. Subsequent follow-up visits are planned at 6, 9, 12, 18, 24, 30, and 36 months after the start of radiotherapy. Thereafter, yearly follow-up visits at 48, 60, and 72 months after starting SBRT will be planned after the initial 3-year follow-up period. M72 visit corresponds to the end of study visit.

Inclusion Criteria:

• Biochemical recurrence occurring at least 2 years after external radiotherapy for prostatic adenocarcinoma by the Phoenix definition (PSA nadir + 2 ng/mL)
• T1-T2c and PSA ≤20 ng/mL and Gleason score ≤7 at initial diagnosis of prostate cancer before the initial/first treatment.
• Recurrence of prostatic adenocarcinoma proven by histology following radiotherapy by transrectal or transperineal sextant biopsies of the two lobes of the prostate, with a minimum of 12 biopsies, irrespective of Gleason score. Biopsies of the seminal vesicles are optional.
• Clinical stage T1-T2 on relapse; unilateral extracapsular extension (T3a) on MRI permitted except posteriorly relative to the rectum
• Estimated clinical target volume (CTV) / prostate volume < 0.5 based on imaging and biopsies
• Pelvic and prostatic assessment by multiparametric MRI- Absence of pelvic or metastatic recurrence proven by choline PET scan
• Performance status World Health Organization (WHO) 0-1
• PSA level ≤10 ng/mL at baseline (before salvage-SBRT)
• PSA doubling time >10 months
• International Prostate Cancer Score (IPSS) ≤12
• Uroflowmetry with a maximum flow rate >10 mL/s, a postvoid residual urine volume <150 mL, and a urine volume >150 mL.
• No other anti-cancer treatment since the external radiotherapy administered as first-line treatment
• No other anti-cancer treatment planned for the current recurrence
• No contraindication to fiducial marker implants; haemostatic disorders must be corrected before implantation
• Age >18 years
• Life-expectancy greater than or equal to 5 years (Lee scale)
• Patient registered with a health insurance system
• Patient who has signed the informed consent form
• Patients willing and able to comply with the scheduled visits, treatment plan, laboratory tests, and other study procedures indicated in the protocol.

Exclusion Criteria:

• Lymph node or metastatic spread
• Late post-radiotherapy urinary or gastrointestinal toxicity of grade ≥2 (following primary radiotherapy)
• Other cancers in the last 5 years except for non-melanoma-type skin cancer
• History of inflammatory bowel disease
• Anticoagulant treatment
• Contraindications to undergoing MRI
• Prostate volume >80 cc
• Transurethral resection of the prostate (TURP) in the 6 months before registrations
• Presence of rectal telangiectasia grade 3 classified by the Vienna Rectoscopy Score (obligatory rectoscopy)
• Previous rectal surgery
• Patients unable to undergo medical follow-up in the study for geographical, social or psychological
• Person deprived of their liberty or under protective custody or guardianship
• Patients enrolled in another therapeutic study

All patients during the SBRT planning with a ratio of clinical target volume (CTV) / prostate volume >0.5 will be withdrawn from the study. These patients will be considered as not evaluable and will not be treated within the context of the study.