Advanced Skills in Modern Radiotherapy 2018

Bow Tie Filters

• Decrease patient dose

• Two types used in different modes: Full fan or half fan mode

• Full fan mode: image is acquired at the central axis on the detector panel and images acquired from 200 0 rotation

• Half fan mode: the detector is offset laterally acquiring only half of the projection of the patient ➢ Detector panel is offset laterally, rotates a full 360 o captures only half a projection and reconstructs the image from that ➢ Recommended for larger FOV (pelvis) ➢ Half fan filters result in the greatest HU discrepancy b/w CT and CBCT (Ding et al., Yoo and Fang-Fang, Seet et al. )