Single-channel axial and helical CT of the pituitary gland is best performed in the direct coronal plane by maximally extending the patient's neck while the patient is either supine or prone. This method allows for the demonstration of pituitary abnormalities with radiation dose to the lens that is lower than that possible with axial imaging."
In the supine or prone position one still has to avoid fillings. Both positions can be difficult to maintain raising the probability of motion artifact. The primary benefit in older scanners imo is getting scans perpendicular to the floor of the sella.
Streak artifacts are reduced because when scannedsupine the petrosa are in plane, when scanned prone the beam travels through the "short plane"petrous ridges