Dose Escalation to Dominant Intraprostatic Lesions (DIL) With MRI-TRUS Fusion High Dose Rate (HDR) Prostate Brachytherapy

Overview

The Magnetic Resonance (MR) provides high resolution of soft tissue images allowing an appropriate assessment of the local extent of the disease. Recent studies have shown an increase in sensitivity and specificity for the detection of Dominant intraprostatic lesions when using multiparametric MRI as a diagnostic tool in the staging of the disease. Among the various irradiation techniques currently available for prostate cancer, Brachytherapy is the superior in terms of dose conformation; this conformation allows greater dose escalation, adjusting the isodoses to the prostate with exquisite accuracy, keeping healthy adjacent organs, such as the urethra and rectum, in a tolerable dose range Brachytherapy companies have recently developed software allowing for TRUS-MR image fusion. The purpose of this study is to demonstrate the feasibility of the delivery of a higher than prescription dose to the dominant intra-prostatic nodule as defined on multiparametric MRI. Dose to prostate, and adjacent structure will remain the same as the current treatment practice. Timing and the delivery of brachytherapy will not change from our current practice

Treatment: The patient's treatment will consist of combined Hypofractionated external beam (3750 cGray in 15 fractions) and MRI-TRUS fusion HDR brachytherapy boost (1 fraction of 1500 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)and Organs at risk (OARs) urethra and rectum are delineated. A transrectal sagittal volumetric ultrasound image is immediately adquired 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: The homogeneity parameters used for optimization aim for prostate V100 \> 98%, V150 of 25-33%, V200 \< 8%, where Vn is the fractional volume of the organ that receives n% of the prescribed dose, urethral dmax \< 115% and rectal 1cc \< 70% of prescribed dose. The treatment plan will be manipulated such that the normally occurring high dose regions (125%, 150%) are positioned at the site of the identified disease Endpoints Feasibility of higher doses administration, toxicity and efficacy will be measured