Frequency and Classification of Radiation-induced Diarrhoea in Patients with Prostate and Rectal Cancer During Curative External Radiotherapy

1. Background Prostate and rectal cancer are among the most common cancer types in Denmark and make up the majority of patients who receive curative radiation therapy of the small pelvis. A well-known side effect of external beam radiation therapy (EBRT) to the pelvis is radiation-induced diarrhoea (RID). When ionising radiation is given to the patient, both tumour and the surrounding cells are damaged. Thus, irradiating prostate and rectal cancer will inevitably lead to the damage of the nearby gut mucosa cellular components. This cellular damage is causing the RID. RID is reported as the problem with the greatest impact on health-related quality of life (QoL) and social behaviour.

Up to approx. 70% of patients who receive pelvic radiation experience acute RID. It usually occurs two weeks after start of EBRT and peaks during 4-5 weeks. Acute RID may cease a few weeks after the end of EBRT but increases the risk of developing chronic RID.

Recently, a systematic Cochrane review reveals low evidence for dietary interventions in RID due to few studies and low scientific quality. A serious drawback of the Cochrane review was that it included studies prior of 2005, with radiotherapy given both pre- and post-surgery, as well as with radiotherapy techniques resulting in higher doses to the normal tissue. It is well known that the volume of the radiation field greatly impacts the severity of RID and newer radiation techniques allow smaller volume fields.

There is a lack of consensus about how acute RID is reported, such as definition of RID (frequency), classification and the changes during EBRT. There is also a lack of knowledge of changes in microbiomes which can contribute to RID. The role of dietary intervention during EBRT could also influence RID. 2. Aim The aim of this prospective observation study is to investigate the frequency, severity and changes of acute RID in patients with prostate and rectal cancer as well as the role of nutrition and changes in microbiome during curative EBRT. 3. Method This is an observational multicenter study of acute RID in patients with prostate and rectal cancer during curative EBRT. The study will take place in parallel with the patients' EBRT, which is ongoing on weekdays over 39 days for patients with prostate cancer and 28 days for patients with rectal cancer.

Study procedure Candidates will be identified according to the inclusion and exclusion criteria. The patients will be informed orally and in written form by a doctor or project nurse at the first oncology appointment.