Ultra Hypofractionnated Radiotherapy With HDR Brachytherapy Boost.

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.