Phase I Study MR-guided SBRT to PCa

Inclusion Criteria: * Histologically confirmed prostate adenocarcinoma. * Patients with low or favorable intermediate risk prostate cancer and patients with unfavorable intermediate risk prostate cancer who decline androgen deprivation therapy * Pretreatment evaluations must be completed as specified in Section 4.0 * Patients must sign a study-specific informed consent form prior to study participation. * No contraindication to MRI. For example, patients with metal fragments or implanted devices such as pacemakers and aneurysm clips may not be eligible for the study * At least one intraprostatic lesion can be identified on the mpMR images. * Patients agree to have hydrogel placed. Exclusion Criteria: * Patients who have a contraindication to contrast-enhanced MRI are not eligible. Patients with an implanted device such as a pacemaker or metal fragments are not eligible.