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Initial Clinical Experience with Brainlab ExacTrac 6D for Frameless SRS and Cross Comparison with CBCT

D Mynampati

D Mynampati*, H Kuo , R Yaparpalvi , K Jeong , M Garg , A Basavatia , W Tome , Montefiore Medical Center, Bronx, NY


WE-RAM1-GePD-J(A)-4 (Wednesday, August 2, 2017) 9:30 AM - 10:00 AM Room: Joint Imaging-Therapy ePoster Lounge - A

Purpose: To understand initial setup shifts of ExacTrac6D frameless SRS system and compare its residual shifts with CBCT.

Methods: For this study, we analyzed the initial setup shifts and residual shifts of 21 frameless SRS treatments treated using Brainlab, ExacTrac6D and TrueBeamSTx. Initial setups are performed using Brainlab mask system and cranial optical guidance array. These setups are corrected using Brainlab ExacTrac x-ray and 6D-couch. After applying initial setup shifts, verification images were acquired using ExacTrac x-ray and TrueBeam CBCT. Our tolerances for ExacTrac6D are 0.7mm and 1.0degree for translational and rotational shifts. CBCT online match translational shifts tolerance is 1mm. To compare residual shifts of ExacTrac with CBCT, planning CT and CBCT were re-registered at Varian, Eclipse registration module and translation and rotational shifts were recorded. For analysis, Mean(x) Standard deviation (SD) and Root mean square (RMS) of initial and residual shifts were computed. RMS difference between ExacTrac residual shifts and CBCT re-registration shifts were recorded. Wilcoxon rank test is applied to residual shifts to determine the difference between two modalities (p<0.05 was considered as statistically significant).

Results: Initial setup’s largest values of mean, SD and RMS of translational shifts are 2.02mm(lateral), 2.18mm(longitudinal) and 2.32mm(lateral). Similarly, for rotational shifts they are 0.77degree(yaw), 1.3degree(yaw) and 1.49degree(yaw) respectively. RMS difference between ExacTrac x-ray residual shifts and CBCT re-registration shifts are within <0.3mm and <0.4degree. Wilcoxon rank test p-values are 0.03(lateral), 0.781(longitudinal), 0.026(Vertical), 0.029(pitch), 0.126(roll) and 0.476(yaw).

Conclusion: Initial shifts shows that the average frameless mask reproducibility is around 2mm and 1degree. There were no significant differences between CBCT and ExacTrac in 3 out of 6 shifts. The differences are within the width of the CBCT voxel and are within 1mm and 1degree. Using a 6D couch, acceptable setup accuracy for frameless SRS treatments can be achieved with both verification methodologies.

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