AbstractID: 7986 Title: Inter-user Variability of the BAT Ultrasound System
The BAT (NOMOS Corp. Sewickley, PA) is an ultrasound-based system that can be used for daily prostate localization and repositioning.
After preliminary alignment of the patient and the acquisition of two suprapubic ultrasound images, the user is prompted to align a patientspecific CT structure set onto these ultrasound images. Based on this alignment, required couch shifts to reposition the prostate in the beam
port are calculated. The purpose of this work is to investigate the inter-user variability of the alignment process. Out of a group of eight
possible users, typically 5-6 users independently aligned the structure set on the same set of ultrasound images. All patients had gold seeds
implanted in their prostate. Using an a-Si flat panel portal imager, the location of these markers is visualized and compared to their
expected location. Patient shifts based on the seed location served as a standard for comparison. To date data for 23 days are available. On
average, a daily range of couch shifts of about 6 mm is seen in each direction. If only the more experienced users are included in the
analysis the average range is reduced to 4-5 mm. Occasionally, poor image quality resulted in a large range of shifts. Exclusion of these
images reduces the above results by about 0.5 mm. Compared with the shifts based on the gold seed positions, the average BAT shifts
differed by less than 1.5 mm in the lateral and ant/post directions and by 3.5 mm in the sup/inf direction.