Figure 3. A case from a study of meningiomas of the skull base evaluating the differences between MRI and CT assessment of the clinical target volume(CTV) for radiotherapy. The 3D reconstructed view of the CT-defined CTV (red outlines) and MR-defined CTV (yellow outlines) illustrates the spatial differences in CTV definition by the two different imaging modalities where the MR-defined CTV demonstrates tumour extending laterally along the petrous ridge that was not seen using CT [15].