This is a pilot study to prospectively investigate potential predictive imaging and genomic biomarkers for patients with high-risk prostate cancer treated with standard of care EBRT + BTX + ADT. The primary imaging modalities that will be evaluated will be PSMA positron emission tomography (PET) and multi-parametric magnetic resonance imaging (MRI). Pre-treatment PET/MRI scans will also be obtained as part of standard of care prior to study enrollment. Response will be assessed on a mid-treatment PET/MRI scan obtained for research purposes after completion of EBRT but prior to brachytherapy boost. PET/CT (computerized tomography) may be used instead if PET/MRI is not technically possible. Imaging response will be compared to pathology from image-directed prostate biopsies taken at the time of the brachytherapy boost. The primary genomic marker that will be evaluated is a clinically available gene-expression array, Decipher, that will be obtained as part of standard of care prior to study enrollment.