Prostate Radiotherapy Integrated With Simultaneous MRI (The PRISM Study)

Currently radiotherapy for prostate cancer is directed using scans or X-Rays, which ensures the radiotherapy treatment 'hits the target' and avoids the healthy tissues around the prostate. There are two current methods of radiotherapy image guidance- either placing small gold seeds into the prostate and taking XRays or doing a small CT scan of the prostate region each day. Neither of these methods are perfect and have drawbacks and inaccuracies. The best way to see the prostate is with an MRI scan - this shows the edge of the prostate much more clearly and can even show the area of most aggressive cancer within the prostate. Shortly the investigators will have the ability to use a new machine - an MR-Linac - which combines an MR scanner and a radiotherapy machine. As well as giving the investigators a clearer picture, and enabling the investigators to keep watching the prostate while the participant has their treatment (not currently possible with standard machines) this new machine will also allow the investigators to change the radiotherapy plan if they can see that the internal anatomy has shifted day to day. Currently the investigators have to give the same radiotherapy plan each day, which means the investigators have to treat a 'safety margin' around to prostate to allow for these day to day anatomy changes (e.g. rectal filling). The aim of this study is to assess the technical feasibility of delivering radical radiotherapy for prostate cancer using the MR-Linac, including the feasibility of changing the radiotherapy plan on a daily basis to mirror internal anatomy changes. The investigators will recruit 30 patients with localised prostate cancer who need radiotherapy. The team will deliver the same dose in the same number of days i.e. the same as standard radiotherapy. Side effects will also be assessed by physicians and using patient questionnaires.