Multi-parametric MRI-guided focal tumor boost using HDR prostate brachytherapy: A feasibility study

PURPOSE: This study investigates the feasibility of delivering focal boost dose to tumor regions, identified with multi-parametric MRI, in high-dose-rate prostate brachytherapy. METHODS AND MATERIALS: T2-weighted, diffusion-weighted, and dynamic-contrast-enhanced MRI were acquired the day before treatment and analyzed retrospectively for 15 patients. Twelve patients had hormone therapy before the MRI scan. The tumor was delineated on MRI by a radiologist and registered to treatment planning transrectal ultrasound images. A margin based on analysis of delineation and registration uncertainties was applied to create a focal boost planning target volume (F-PTV). Delivered treatment plans were compared with focal boost plans optimized to increase F-PTV dose as much as allowed by urethral and rectal dose constraints. RESULTS: Tumors were delineated in all patients with volumes 0.4-23.0 cc. The margin for tumor delineation and image registration uncertainties was estimated to be 4.5 mm. For F-PTV, the focal boost treatment plans increased median D-90 from 17.6 to 20.9 Gy and median V-150 from 27.3% to 75.9%. CONCLUSIONS: MRI-guided high-dose-rate prostate brachytherapy focal tumor boost is feasible tumor regions can be identified even after hormone therapy, and focal boost dose can be delivered without violating urethral and rectal dose constraints. (c) 2014 American Brachytherapy Society. Published by Elsevier Inc. All rights reserved.