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Direct Clinical Comparison of 2D Versus 3D Transabdominal Ultrasound Image Guidance Methods for Prostate Radiotherapy Treatment

B Salter

B Wang, V Sarkar, P Rassiah-Szegedi, H Zhao, Y Huang, M Szegedi, T Shrieve, JT Tward, BJ Salter*, University of Utah, Salt Lake City, UT

SU-E-U-9 Sunday 3:00PM - 6:00PM Room: Exhibit Hall

Purpose: Direct clinical comparison of 2D versus 3D transabdominal ultrasound image guidance (USIG) methods for prostate radiotherapy

Methods: Image guidance shifts were compared on the same subject, same treatment session between Nomos BAT and Elekta Clarity ultrasound methods for 20 patients and 662 prostate treatments. Both systems use unique approaches to USIG. BAT system acquires two static 2D ultrasound images (axial and sagittal) and compares them to contours derived from simulation CT (i.e. intermodality comparison). Clarity system acquires a 3D ultrasound data set at CT simulation and compares to treatment-day 3D ultrasound image set for deriving image guidance shifts (i.e. intramodality comparison). In this study, transabdominal Clarity image guidance was performed and the shifts were implemented first. Then transabdominal ultrasound images were acquired approximately 1minute later with BAT to derive image guidance shifts. These BAT-reported shifts were recorded as the difference between BAT and Clarity USIG. The same experienced operator performed both BAT and Clarity paired alignments.

Results: The average differences between the two systems were less than 1.0 mm in all three principle directions. The average standard deviation of these differences in lateral, vertical, and longitudinal direction were 1.2, 1.7, and 1.4 mm, respectively. Average Max difference (across all patients) was 1.9 mm; absolute Max across all image sessions was 10.2 mm. Differences between the two USIG approaches can be partially explained by prostate motion as a function of the time elapsed between imaging sessions, and 10.2 mm Max is not inconsistent with prostate motion we have observed during a similar time frame when using Calypso RF tracking.
Results were further stratified into two groups: intact prostate and post-prostatectomy, and no systematic differences were observed between these two groups.

Conclusion: Good agreement was observed in this head-to-head comparison study between BAT and Clarity USIG methods for prostate localization.

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