Dose Escalation For INtraprostatic LEsions

Inclusion Criteria: * Histologically confirmed adenocarcinoma of the prostate * Unfavourable intermediate-risk or high-risk localized disease * Unfavourable intermediate-risk prostate cancer is defined as intermediate-risk prostate cancer \[that is, no high-risk features and one or more intermediate-risk factors: T2b-T2c, Gleason 3+4 (grade group 2) or Gleason 4+3 (grade group 3), or PSA 10-20 μg/L\] and one or more of the following: 2 or 3 intermediate-risk factors; Gleason 4+3 (grade group 3); ≥ 50% biopsy cores positive * High-risk localized prostate cancer is defined as at least one of the following: T3a-T3b; Gleason ≥ 8 (grade group 4 or grade group 5); PSA \> 20 μg/L * 3 Tesla prostate MRI done no more than 12 months prior to enrollment * ECOG performance status 0-2 * Age ≥ 18 years * Written informed consent * The participant has planned androgen deprivation therapy that meets one of the following criteria: * Patients with intermediate-risk localized prostate cancer who have planned androgen deprivation therapy consisting of up to 6 months of triptorelin with or without bicalutamide; OR patients with high-risk localized prostate cancer who have planned androgen deprivation therapy consisting of up to 24 months of triptorelin with or without bicalutamide. * Completion of all appropriate investigations prior to enrollment Exclusion Criteria: * Evidence of pelvic nodal metastases or distant metastases (AJCC Stage T1-4 N1 M0-1 or T1-4 N0 M1 disease) * Discordance between pre-enrollment prostate MRI and prostate biopsy findings, defined as biopsy cores with Gleason Gleason ≥ 4+3 (grade group ≥ 3) adenocarcinoma with no corresponding tumour focus seen on MRI * Androgen deprivation therapy commenced more than 60 days prior to enrollment * Intention to electively treat the pelvic lymph nodes with radiotherapy * Other active malignancy within the previous three years (except adequately treated nonmelanomatous carcinoma of the skin or low-grade superficial bladder carcinoma) * Prior pelvic radiotherapy * Contraindication to pelvic radiotherapy * Any history, past or present, of inflammatory bowel disease * Unilateral or bilateral hip arthroplasty * Trans-urethral resection of the prostate (TURP) performed within 6 months of anticipated start date of radiotherapy * Patients must not concurrently participate in any other therapeutic prostate cancer trial.