Figure 3. (Left to right): methionine (MET)-PET, CT with contrast and T₁ MRI with gadolinium (Gd) were co-registered and integrated in the radiation treatment planning of a patient with astrocytoma (WHO stage III), 2 weeks after surgery. The residual tumour (shown by the area of increased MET uptake on the PET scan) is delineated in pink. This region was delineated as the gross tumour volume and was treated with a higher dose (the isodose distribution for the boost volume is shown in green). The yellow arrows show a region of contrast enhancement without MET uptake on PET — this was considered to be due to disturbance of the blood–brain barrier (BBB) as a consequence of surgery and was excluded from the high-dose irradiation area. In this case, MET-PET helped to differentiate between the areas of contrast enhancement due to BBB disturbance after surgery and those due to residual tumour. The PET studies were performed in co-operation with the Department of Nuclear Medicine, Technical University Munich, Director Prof. Dr M Schwaiger, Germany.