(Sunday, 7/12/2020) [Eastern Time (GMT-4)]
Room: AAPM ePoster Library
Purpose: Radiosurgery (SRS) requires submillimeter accuracy in treatment delivery. The purpose of the study is to evaluate the performance of two orthogonal radiographic imaging systems for SRS pre-treatment patient positioning verification.
Methods: institutional SRS pre-treatment verification imaging protocol calls for 2-D orthogonal radiographic imaging with either ExacTrac (ET, BrainLab, Munich, Germany) or On-Board Imager (OBI, Varian Medical Systems, Palo Alto, CA) followed by 3-D volumetric imaging with CBCT. We retrospectively reviewed the images of 96 SRS patients treated in 2019 to assess the performance of ET and OBI in comparison with CBCT. A total of 103 imaging sessions of OBI+CBCT were performed for 37 patients while 231 imaging sessions of ET+CBCT were performed for 59 patients. Using CBCT as the gold standard, the additional shifts required by CBCT after the initial shifts determined by OBI or ET imaging were analyzed and compared.
Results: means and standard deviations of vertical/longitudinal/lateral/pitch/roll/yaw shifts by CBCT were 0.49±0.38mm/0.29±0.31mm/0.27±0.28mm/0.18±0.18°/0.19±0.19° /0.27±0.27° post ET imaging shifts, and 0.21±0.17mm/0.29±0.23mm/0.32±0.24mm/0.26±0.23°/0.19±0.21°/0.15±0.17° post OBI imaging shifts. OBI performed better with vertical and yaw corrections (p < 0.05) while ET performed better with lateral and pitch corrections (p < 0.05).
Conclusion: orthogonal radiographic imaging with ET and OBI both yielded reasonable positioning accuracy for SRS treatment compared to 3-D volumetric CBCT imaging. ExacTrac performed better in lateral and pitch corrections (p < 0.05) than OBI while OBI performed better in vertical and yaw corrections (p < 0.05) than ExacTrac.
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