A Pilot Study of Dose dE-eScalaTion IN prostATe radIOtherapy usiNg the MRL

Trial design: A single centre phase II non-randomised study Trial population: Men with intermediate risk localised prostate cancer Recruitment target: 20 patients in total Trial objectives: * Primary To develop a 5 fraction de-escalated dose SBRT protocol capable of reducing side effects * Secondary * To assess levels of acute GU and GI toxicity (CTCAE) * To assess levels of late GU and GI toxicity (CTCAE) * To assess late sexual quality of life (expanded EPIC, IIEF-5) * To assess biochemical relapse-free survival at 2 years Trial treatment: All radiotherapy will be delivered on the MR-linac. Intraprostatic dose will be varied according to risk of local recurrence, based on mpMRI, PSA and histology. The whole prostate will receive 30 Gy in 5 fractions and the GTV plus intra-prostatic margin will receive an isotoxic 45 Gy prescription.

Primary endpoint: Technical feasibility of treating prostate cancer with toxicity- minimising radiotherapy on an MR-linac Secondary endpoint: * Physician reported GU and gastrointestinal (GI) toxicity (CTCAE grade) at baseline and the end of treatment then at 4 weeks and 3 months post-treatment. * Late toxicity (CTCAE v5.0) at 1 and 2 years post-treatment * Patient-reported outcome measures (PROMs) from the EPIC-26, IPSS, and IIEF-5 questionnaires. Patients will be asked to complete PROMs at 4 weeks, 3 and 6 months, 1 and 2 years post treatment. * PSA control and kinetics at 2 years post-treatment Quality of life: EPIC-26 QoL will be measured at baseline, then at 4 weeks and 3, 6, 12 and 24 months from end of treatment. IIEF-5 will be completed at baseline and months 6, 12 and 24. IPSS will be measured at all time points. Follow-up: Patients will be assessed at 6, 12 and 24 months and then as per standard of care.