In the UK over 22,000 people undergo pelvic radiotherapy treatment per year, for several types of cancers including prostate cancer. The investigators want to investigate whether there are any differences in the bacteria in the bowel in patients with prostate cancer and whether these change during treatment. The aim of this study is to analyse the bacteria from the stool of patients undergoing radiotherapy for prostate cancer. The investigators will also look for any changes in the urine, blood and using rectal swabs that might be a surrogate for what is happening in the gut at the same time. They will collect food frequency/ food diary information for each patient alongside health questionnaires. The investigators aim to recruit approximately 50 patients diagnosed with prostate cancer due to undergo radiotherapy over a two year period. Patients will be recruited across 2 sites (Rosemere Cancer Centre, Lancashire Teaching Hospitals Trust and The Christie NHS Foundation Trust).