Single Fraction Real-time High-Dose-Rate Brachytherapy in Patients With Low and Intermediate Risk Prostate Cancer

Treatment: The patient´s treatment will consist of MRI-TRUS fusion single HDR brachytherapy fraction (1 fraction of 1900 cGray). Brachytherapy performed under general anesthesia as an outpatient procedure TRUS-MRI fusion: T2 axial volumetric sequence (VISTA) is imported directly from the picture archiving and communication systems (PACS). Then MR images are reconstructed and segmented. Target volumes (prostate gland, dominant intraprostatic lesions (DILs) Organs at risk (OARs) urethra and rectum are delineated. A transrectal sagittal volumetric ultrasound image is immediately acquired every 2 degrees, a rapid reconstruction algorithm converts the series of 2D images into a 3D volume, which is then displayed in axial, sagittal and coronal views and transferred to the module of fusion with the MRI. The MRI images and the real-time sonography examination are displayed on a split-screen with the possibility of overlaying the images live in one image. A graphical user interface is used for rigid manual registration of the ultrasound and MRI volumes. This interface allows for displacements in the three dimensions and rotations, until both images are correctly superimposed. Then the contoured structures are transferred to the US dataset, and these contours are slightly modified until a perfect matching with the US images is achieved. Dose prescription: Ultrasound images with the catheters in place will be exported to Oncentra Prostate. The prostate, Foley catheter and anterior rectal wall will be contoured. Catheters will be reconstructed on the planning system. Anatomy based inverse planning will be used for dwell time optimization. The homogeneity parameters used for optimization aim are: -For prostate V100 \> 95%, V150 \<35%, V200 \< 6%, where Vn is the fractional volume of the organ that receives n% of the prescribed dose. The dose constraints for the organ at risk will be: * Urethral dmax \< 110% and * Rectal 1cc \< 60% of prescribed dose. Endpoints Feasibility of higher doses administration, toxicity and efficacy will be measured