CT-examinations are used in computer programs which are used in the planning of external radiation of cancers in the anal canal. In CT the structures of the anal canal are hardly visible. 3D-ultrasound examinations offer a better visualisation of normal and pathological structures of the anal canal. The description of the tumour made from the 3D-ultrasound examination is used in the planning of the external radiation.

PET-CT is used to visualise tumour activity also in lymp nodes. The hypothesis of the study is that image fusion of PET, CT and 3D-ultrasound will offer better visualisation of tumour and hereby more accurate diagnostics and treatment.