 The aim of high dose radiotherapy treatment is to deliver enough radiation to the tumour to kill all the cancer cells while at the same time giving a low dose of radiation to the normal parts of the body to reduce the side effects of treatment. This requires the cancer specialist to accurately identify the areas of cancer on a computed tomography CT scan. Positron emission tomography computed tomography PETCT scans use radioactive sugar that is injected into the patient. This sugar goes into cancer cells and shows up as a bright spot on the PET scan, allowing the doctors to see tumours more accurately. Some cancers move with breathing, for example lung, pancreas and oesophageal or gullet cancers. Fourdimensional CT scanning 4DCT is a special type of CT scan that allows the motion of the tumour to be seen and measured accurately. This information can then be used to help ensure that the radiotherapy correctly treats the moving tumour. 