Prior to the commencement of treatment each patient will have a special scan called a PET scan. Patients will receive a second PET scan two weeks after the start of standard chemotherapy. The changes between the two scans will then be used to allocate treatment into the different arms of the study. All study subjects will be randomised to receive either the standard radiotherapy dose or the high radiotherapy dose. The participants that do not respond to the first cycle of standard chemotherapy will be eligible to take part in the aspect of the trial looking at an alternative chemotherapy regimen. Patients will be randomised as follows;