THE EFFECT OF OUT-OF-PLANE PATIENT SHIELDING ON CT RADIATION EXPOSURE AND TUBE CURRENT MODULATIONS: A PHANTOM STUDY ACROSS THREE VENDORS.

The aim of this study was to evaluate how out-of-plane patient shielding affects radiation exposure parameters and tube current modulation on different vendors' computed tomography (CT) scanners. Helical CT scans were performed using two homogenous phantoms to mimic patient attenuation. Four CT scanners from three vendors were investigated by varying the distance of the patient shield from the border of the imaging volume. Scans were performed with a shield placed before and after the localizer. Changes in volume computed tomography dose index (CTDIvol), dose-length product (DLP) and tube current-time products were studied. Out-of-field lead shield increased the CTDIvol and DLP values for each scanner at least for one scan setting when the shield was present in the localizer. The most notable changes were recorded with >1.3 pitch values when the shield was closest to the scanned volume (2.5 cm), and the scan direction was towards the shield. The usage of patient shields in the localizer CT scans can disturb TCM even when placed 7.5 cm away from the edge of the scan.