RHYTHM-I: Modulation of Radiotherapy According to HYpoxia: Exploiting Changes in the Tumour Microenvironment to Improve Outcome in Rectal Cancer.

A low level of oxygen in cancer cells makes them less likely to respond to chemotherapy and radiotherapy treatments. There is interest in using new drugs that improve the level of oxygen in tumours. Another approach would be to increase the radiotherapy dose to tumours with low oxygen levels.

Before we can do this for patients with rectal cancer, we need to develop a reliable way of identifying areas of low oxygen within the rectal tumour. This will make us able to tell which patients may be suitable for such a change in their treatment.

Traditionally, the level of oxygen in tumours is measured by inserting a needle into the tumour and measuring it directly. This is not possible in rectal cancer. This study has been designed to identify the best alternative method. We would like to do a blood test, take samples of cancer tissue and some detailed scans (18F-fluoromisonidazole (F-MISO) positron emission tomography, perfusion computed tomography, functional magnetic resonance imaging). The results of these tests will be compared to decide which gives us the most comprehensive and reliable information.

Patients in Group A go straight to surgery. By looking for markers of low oxygen levels on the tumour that has been removed, we will be able to find out which of the study tests performed before the tumour was removed is the best. By repeating the scans we will be able to see how reliable they are and how much they change on a day to day basis. We think that tumours that still have low levels of oxygen after 8 to 10 doses of radiotherapy are the least likely to respond to treatment.

Group B will have scans before radiotherapy treatment and after 8 to 10 doses of radiotherapy to see if we can identify the patients that have persistent low levels of oxygen.