Ultra Hypofractionnated Radiotherapy With HDR Brachytherapy Boost.

Phase 1-2 study, comparing ultra-hypofractionnated (UH) to a moderately hypofractionnated (MH) radiation therapy, with image guided HDR prostate brachytherapy. Using iso-equivalent doses, a non-inferiority analysis will be done in order to prove UH non-inferior to MH, toxicity wise. Acceptability, tolerability, acute and late toxicity will be reported. MRI visible dominant intra-prostatic lesion will be outlines and variability between radiation oncologists and radiologists will be reported. As secondary objective, biochemical and clinical failure free survival will be reported at 5 \& 10 years.

Phase 1 : consists in a feasibility study (First 28 patients).

Phase 2 : monocentric prospective comparative cohort study.

Recruitment :

* "Centre intégré de cancérologie du CHU de Québec-Université Laval."
* Recruitment period: December 2015 to June 2023

Brachytherapy :

* Implantation under general or spinal anesthesia
* Foley catheter insertion in bladder.
* TRUS prostate localisation.
* Prostate volume measurement.
* Gold fiducial markers (3) insertion.
* Prostate brachytherapy catheters (14 à 21) insertion.
* Cystoscopy for bladder and urethra integrity control.
* Re-insertion of foley catheter after cystoscopy.

Planning imaging: TRUS or CT scan (has needed).

Structures delineation by radiation oncologist (brachytherapist).

* Prostate
* Seminale vesicles
* Rectum
* Colon sigmoïde
* Bladder
* Urethra
* Penile bulb

Dosimetric optimisation

* Oncentra Prostate v. 4.2.2 d'Elekta brachytherapy (Veenendaal, The Netherlands)
* Oncentra Brachy version 4.6 (if under CT scan).

Treatment (brachytherapy dose delivery).

* 15 Gy in one fraction
* Direct interstitial dose monitoring (20 patients or more). Fiber-optic dosimeter inserted in prostate brachytherpy catheter for live dose delivery mesurements.

Foley ablation under full bladder, same day or day after therapy.

Radiotherapy:

* Via IMRT, VMAT or SBRT technics.
* Dose : 25 Gy in 5 fractions administered over a 7 days period. 2 to 3 fractions separated by 2 days, weekend break.
* PTV includes prostate and the first centimeter of seminal vesicle.

Simulation

* one week post brachytherapy
* standard has described in the department procedure manual.
* maximal CT scan slice thickness : 2-3mm.
* uretro-graphy done to identify urogenital sphincter.

Multiparametric MRI

* If no counter-indication and available,
* a T2 tridimensional sequence for prostate delineation
* slice thickness : 1 mm.
* a diffusion weighted sequence will be done.
* a DTI with tractography can be done optionally.
* contrast media (gadolinium) is optional.

Physique

* Linac energy (between 6 MV to 18 MV).
* ARC therapy technique will be used
* planification softwares: Éclipse, Pinnacle or Raystation.
* Portal (kV-kV) imagery will be used for marker match.
* CBCT will be done at each fraction delivered.

Clinical and dosimetric data will be collected prior treatment.

Primary objectives :

* Toxicity analysis will be quantitatively evaluated using CTCAE (v5) at 1, 2 and 5 years post-therapy, and has needed at FU visits. Kaplan-Meier statistical analysis will be used to report toxicity evolution through time.
* median IPSS scores will be reported at 3, 6, 12 months and yearly (1, 2, 3, 4 et 5) post-therapy. IPSS median time to baseline return will be calculated.
* IPSS urinary scores, sexual function (SHIM) and GI toxicity (CTCAE-v5) and quality of life questionnaires ( EPIC-26) will be given at 3, 6 months and yearly thereafter (1, 2, 3, 4 et 5) post-treatment.

Secondary objectives : Biochemical disease-free survival has per Phoenix definition (by American Society of Radiation Oncology - ASTRO) recommendation will be reported using Kaplan-Meier analysis.

Eligibility Criteria:
Inclusion Criteria:

* Biopsy proven Prostate adenocarcinoma
* Stage T1c, T2 (Annex 2)
* Stage Nx or N0
* Stage Mx or M0
* PSA \< 20ng/ml
* Gleason Score 6 or 7
* Having the ability to sing a written consent

Exclusion Criteria:

* Age \< 18ans
* Clinical Stage T3 or T4
* Stage N1
* Stage M1
* PSA \> 20
* Gleason Score 8 to 10
* IPSS Score \> 20 alpha-blocking medication.
* Prior pelvic radiotherapy.
* History of active collagenosis (Lupus, Sclerodermia, Dermatomyosis)
* Past history of Inflammatory Bowell Disease
* Bilateral hip prosthesis