This study aims to test the hypothesis that insertion of an endorectal balloon into a patient receiving radical prostate radiotherapy by treatment radiographers is feasible without the patient experiencing undue discomfort. In addition this study will test the hypotheses that insertion of the rectal balloon prior to radiotherapy delivery stabilises rectal volume during radiotherapy treatment and minimises organ motion within the pelvis.

Inclusion Criteria:

• Age greater than or equal to 18 years
• ECOG performance status 0-2 (Patients with PS-2 as a result of comorbidity will be excluded).
• Patients with histologically confirmed diagnosis of prostate adenocarcinoma
• Patients who are going to undergo treatment with radical radiotherapy for prostate cancer.
• Patients must be able to receive and understand verbal and written information regarding the study and give written, informed consent
• Patients must be able to comply with trial requirements.

Exclusion Criteria:

• Patients must not have a history of previous bowel surgery involving the rectum or anus.
• Evidence of significant clinical disorder or laboratory finding which, in the opinion of the investigator makes it undesirable for the patient to participate in the trial, as well as any other serious uncontrolled medical condition.
• Any patient with a medical or psychiatric condition that impairs their ability to give informed consent
• Pre-existing anorectal disease, e.g. Haemorrhoids, active bleeding, anal irritation, inflammatory bowel disease.
• Patients who are unable to give consent.
• Patients in clinical trials of new investigational medicinal products or treatment regimens unless there is written, prior agreement that the patient can also consent to this study, and that clinical data can also be used for this study.
• Prior pelvic radiotherapy