Focal Versus Whole Gland High Dose-Rate Brachytherapy (HDR-BT) Boost to External Beam Radiotherapy in Localized Prostate Cancer: A Phase 2 Randomized Trial

Inclusion Criteria: * Histologically confirmed diagnosis of adenocarcinoma of the prostate * Eastern Co-Operative Oncology Group (ECOG) 0-2 * Intermediate and high-risk disease with localized unfavorable features: * defined as clinical stage tumor cT1 or cT2a, International Society of Urological Pathology (ISUP) grade group 2-4 in less than or equal to 50% of the cores, unilateral extracapsular extension (ECE), prostate specific antigen (PSA) less than or equal to 20 ng/mL * corresponding to an Identified dominant intraprostatic lesion (DIL) on multiparametric magnetic resonance imaging (mpMRI) Prostate Imaging Reporting and Data System score (PI-RADs 3-5) * Prostate volume less than or equal to 60 cc is recommended. Transrectal ultrasound (TRUS) and magnetic resonance imaging (MRI) are accepted to assess prostate volume. Patients with a prostate volume between 60 and 80 cc can be included if the International Prostate Symptom Score (IPSS) is less than 15 and brachytherapy is deemed feasible by the treating physician. Exclusion Criteria: * Contraindications to mpMRI * Documented nodal or distant metastases * Previous pelvic radiotherapy * Recent transurethral resection of prostate (less than or equal to 6 months), previous prostatectomy or high-intensity focused ultrasound (HIFU) * Poor baseline urinary function: International Prostate Symptom Score (IPSS) greater than 19 * Connective tissue disease or inflammatory bowel disease * Patients deemed unsuitable for general anaesthetic by the Anaesthesia Department * Patient is unable to lie flat long enough for the Radiation Therapy (RT) Simulation and Treatment