Dose De-escalation in Prostate Radiotherapy Using the MRL

The goal of this feasibility study is to learn about dose de-escalation in the treatment of men with intermediate risk prostate cancer.The main question it aims to answer is the technical feasibility of treating prostate cancer with toxicity-minimising radiotherapy on an Magnetic Resonance Linear Accelerator (MR-linac). It will also examine gastrointestinal and genitourinary toxicity in the acute and late setting post radiotherapy as well as Prostate-Specific antigen (PSA) control up until 2 years post treatment.Participants will be treated with radiotherapy to the prostate with which will be given in 30Gy in 5 fractions to the whole prostate and 45Gy in 5 fractions to the dominant lesion.

Inclusion Criteria:Men aged ≥18 yearsHistological confirmation of prostate adenocarcinoma requiring radical radiotherapyGleason score 3+3, 3+4 or 4+3 (Grade groups 1, 2 or 3)MRI stage T2 or less (as staged by AJCC TNM 2018)MRI-visible tumour(s) of Prostate Imaging-Reporting and Data System (PIRADS) v2 grade 3 or higher on T2 and diffusion-weighted imaging and/or dynamic contrast-enhanced imaging with concordant pathologyTumour nodule visible on MRI occupying <50% of prostate on any axial slice and <50% total prostate volumePSA <20 ng/ml prior to starting androgen deprivation therapy (ADT)Patients can be concurrently treated with androgen deprivation therapy if this would be standard of care. Luteinizing hormone-releasing hormone (LHRH) analogues or Bicalutamide are permitted. ADT is not mandatory where this would usually be omitted.World Health Organisation (WHO) Performance status 0-2Ability of the participant understand and the willingness to sign a written informed consent form.Ability/willingness to comply with the patient reported outcome questionnaires schedule throughout the study.Exclusion Criteria:Contraindications to MRI (e.g. pacemaker, potentially mobile metal implant, claustrophobia)IPSS 19 or higherHigh grade disease (GG3) occult to MRI-defined lesionPost-void residual >100 mls, where knownProstate volume >90ccComorbidities which predispose to significant toxicity (e.g. inflammatory bowel disease) or preclude long term follow upUnilateral or bilateral total hip replacement, or other pelvic metalwork which causes artefact on diffusion-weighted imagingPrevious pelvic radiotherapyPatients needing >6 months of ADT due to disease parameters.Previous invasive malignancy within the last 2 years excluding basal or squamous cell carcinomas of the skin, low risk non-muscle invasive bladder