Retreating localised prostate cancer with either repeat radiotherapy or brachytherapy

INTERVENTION: Phase 1‐ Recruitment and registration: This two‐arm randomised (1:1) feasibility study will aim to prospectively recruit 30 patients over 24 months into each treatment arm (BT and SABR) giving a total of 60 patients in the study. This accounts for any dropouts resulting in incomplete data sets. Suitable patients meeting the inclusion criteria for the study will be identified via the Leeds, the Christie, and Mount Vernon Hospital Prostate MDT meetings which encompass the local surrounding district general hospitals. Suitable trial patients will be invited to take part in the study during their routine clinical appointment with the treating clinical oncologist and provided with written patient information sheets and if the patient is willing to take part they will be consented to join the trial. After being given verbal and written information about the study in the routine outpatient clinic, potential participants will be given sufficient time to consider participation (at least 24 h). A member of the research team will call the patient in the following week after the initial outpatient clinic to follow‐up whether the patient would like to take part. If the patient wants to take part, a physical consent form will be sent out to the patient for them to sign and send back. A telephone or face to face appointment will also be offered to the patient if they want to discuss the study involvement in greater detail. Prior to the trial recruitment stage, all patients will have received standard of care prostate MRI scans and a prostate biopsy to confirm they have local recurrence of their prostate cancer. As part of the standard care, all patients will also have baseline blood tests including prostate specific antigen (PSA) and testosterone levels. Once a participant is deemed CONDITION: Prostate cancer ; Cancer PRIMARY OUTCOME: Feasibility measured using overall, and recruitment site‐specific recruitment rates collected monthly over the 24‐month recruitment period SECONDARY OUTCOME: 1. Toxicity following salvage ultra‐hypofractionated external beam radiotherapy (EBRT) or high‐dose rate brachytherapy (HDR‐BT) to inform future RCT design will be measured using: ; 1.1. Patient‐reported outcome measures (PROMs) in terms of impact on quality of life and urinary, bowel, and sexual function using the EPIC‐26, EORTC QLQ‐C30, and IPSS questionnaires at baseline, 1, 3, 6, 12, and 24 months; 1.2 Clinician‐reported toxicity outcomes collected using Common Terminology Criteria for Adverse Events (CTCAE) version 5.0 at baseline, 1, 3, 6, 12, 18, and 24 months ; 2. Identification of MRI biomarkers that may be predictive of genitourinary and gastrointestinal toxicity (measured by PROMs as detailed above) using multiparametric MRIs at baseline and at 1‐month and 1‐year post‐treatment ; 3. Image quality and repeatability of prostate functional imaging for detecting hypoxia measured using the diffusion coefficient (D), perfusion fraction (f), and pseudo‐diffusion coefficient (D*) on IVIM sequences and the rate of relaxation per second (R2*) on BOLD sequences at 1‐month and 1‐year post‐treatment; 4. Changes in a hypoxia‐associated gene signature and proteomic/cytokine signatures following primary radiation (and exploration of the prognostic value of such changes) measured using blood and urine samples collected at baseline and 1, 3, and 6 months after radiation treatment INCLUSION CRITERIA: 1. Aged =18 years 2. Biopsy‐proven locally recurrent prostate cancer 3. T1‐3 N0 M0 Any Gleason/ISUP grade group adenocarcinoma prostate with most recent PSA <50 ng/ml 4. Baseline plasma testosterone level required 5. Willing and able to provide informed consent 6. Primary prostate cancer treatment must have been with external beam radiotherapy (EBRT) or brachytherapy (BT) 7. Biochemical recurrence at least 2 years after primary radiation treatment completed 8. Performance status WHO 0‐2 9. Reasonable urinary function (IPSS <20 and Qma X>0 ml/s on flow tests) 10. > 10‐year life expectancy 11. No metastatic disease (PET‐CT ‐ any of choline/fluciclovine/PSMA) 12. No prior prostatectomy (TURP >3 months before randomisation is acceptable) 13. No history of inflammatory bowel disease 14. Suitable for procedure under general anaesthesia 15. Androgen Deprivation Therapy may be initiated at the discretion of the treating oncologi