paediatrics Brussels 17

Optic chiasm

• Probably most crucial organ at risk • Lies below hypothalamus, third ventricle and its optic recess • Anterior cerebral arteries lie ventrally, and ICA’s laterally • Approx 14mm transverse width, 8mm AP, 2-5mm height • Slopes slightly upwards and backwards • Must contour on multiple slices – gaps in contour will lead to missing essential volume for computing dose-volume histogram • Check contour on sagittal or coronal images