Figure 2

Prescription isodose distribution in sagittal (A), coronal (B) and axial (C) views of a recurrent pituitary adenoma extending to the parasellar region, and in close proximity of the optic chiasm (contoured in green) and the brainstem (contoured in brown). The target volume (contoured in purple) was created by the geometric expansion of pituitary tumour plus 1 mm. The patient was treated with a linear accelerator (LINAC) stereotactic radiosurgery (SRS) with a single dose of 18 Gy prescribed to the 95 per cent isodose line. The 90 per cent, 70 per cent and 50 per cent isodose curves showing dose levels delivered to surrounding tissues and adjacent critical structures are represented. High-dose homogeneity and conformity was achieved with the use of intensity-modulated stereotactic radiosurgery (IMSRS), in which intensity modulation of dose for each beam is obtained by moving the leaves in the micro multi-leaf collimator during the course of treatment (D). The dose-volume histogram (DVH) graph indicates that doses to optic chiasm (green) and brainstem (brown) were below the tolerance generally accepted for these stuctures (E), while delivering an homogeneus dose to the target volume (purple).