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Session: SBRT/SRS Measurement Techniques [Return to Session]

Target Localization Error Estimation in Linac Based SRS Treatment

S Gholami1*, G Narayanasamy2, F Kalantari2, P Sabouri2, Z Su2, (1) Virginia Commonwealth University, Richmond, VA, (2) University of Arkansas for Medical Sciences, Little Rock, AA


TU-D1000-IePD-F3-1 (Tuesday, 7/12/2022) 10:00 AM - 10:30 AM [Eastern Time (GMT-4)]

Exhibit Hall | Forum 3

Purpose: Investigation of various sources of target localization errors (TLE) is a crucial step for comprehensive QA of stereotactic radiosurgery (SRS) treatment. The objective of this study is to investigate the potential factors that affect the accuracy and precision of SRS treatments.

Methods: 3D Lucy phantom was prepared by placing sub-millimeter solder material at the center of film inside the image cassette. Following CT image reconstruction at 1 mm slice thickness, treatment plans were created in Eclipse ver 15.5 for dose delivery on Varian Truebeam STx with HD-MLCs. The main sources of TLE namely, gantry flex and 6 Degrees-of-Freedom (DOF) couch sag were measured on the Lucy phantom using planar KV, MV, CBCT and ExacTrac imaging systems. TLE arising from gantry flex was estimated along clockwise (CW) and counter-clockwise (CCW) gantry rotation at 30-degree intervals by acquisition of kV-MV image pair of Lucy phantom at a fixed couch position. TLE due to couch sag uncertainties were calculated using CBCT followed by ExacTrac images acquisition at various couch angles from 90° to 270° at 15 degrees intervals in both CW and CCW directions. Reproducibility was performed by repeating these measurements 3 times. TLE values are reported using root mean square error (RMS).

Results: RMS TLE values were 0.07 mm and 0.08 mm for CW and CCW directions of gantry rotation, respectively. Couch sag TLE were 0.65 mm and 0.45 mm along CW and CCW directions, respectively. The maximum reproducibility error (less than tolerance) was 0.11 mm and 0.27 mm for the KV/MV pair and ExacTrac imaging systems, respectively.

Conclusion: In this study we performed a comprehensive QA method to quantify localization errors in SRS treatment procedure. The effect of gantry flex, couch sage and reproducibility of imaging systems used in SRS treatment delivery have been evaluated to be within 1mm.


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