Figure 20. (a) Non-contrast CT scan of the pelvis at the site of the cervical cancer. The estimated gross tumour volume map has been drawn in white. (b) T2 weighted axial fast-spin-echo scan with the gross tumour volume map drawn in yellow. (c) The CT and MRI scans are co-registered and show the two gross tumour volume maps are significantly different. Radiotherapy, usually based on the CT map, appears to have overestimated the gross tumour volume.