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Assessment for Setup Uncertainty of Frameless Localization System of Stereotactic Radiosurgery Using Cone Beam Computed Tomography

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J Baek

J Baek*12, Y Oh2, S Park2, E Choi2, K Jeon2, O Kim 2, J Kim2, (1) Yeungnam University,Dae-dong,Gyeongsan,(2)Dongsan Medical Center, Keimyung University, Jung-gu, Daegu

SU-E-J-17 Sunday 3:00PM - 6:00PM Room: Exhibit Hall

Purpose:
The purpose of this study was to assess setup uncertainties and quantify the magnitudes of setup corrections of frameless localization system using cone beam computed tomography (CBCT).

Methods:
This study involved 28 patients who were treated single fraction stereotactic radiosurgery (SRS) by Varian Clinac IX equipped with a micro-multileaf-collimator (m3). All patients were simulated and setup with BrainLab immobilization mask and localization system, also they underwent a kV-CBCT imaging before treatment. Setup corrections between acquired CBCT and planning CT were performed by automatic adjustment couch system, and collected into registration software as Offline Review (Varian Medical System, Palo Alto, CA) and the data were analyzed in 4 directions: lateral (x) longitudinal (y), vertical (z), rotational (yaw).

Results:
The mean setup corrections were 0.07 mm, -0.43 mm, 0.50 mm, and -0.11° in x, y, z and yaw directions, respectively. The mean radial correction was 1.85 mm. The standard deviations of setup corrections were 0.77 mm, 1.73 mm, 0.69 mm, and 0.40° in x, y, z and yaw directions, respectively. The maximum shifts were 2 mm, -5 mm, 2 mm, and 1° in x, y, z and yaw directions, respectively. The mean setup corrections represent systematic errors of localization system and the standard deviations indicated random setup errors of BrainLab specific thermoplastic mask. The systematic error of localization system was small of less than 0.5 mm or -0.1°, whereas patient random errors still inherent and the largest magnitude of setup error was -5 mm in y direction. There were rotational setup errors and the highest magnitude was 1°.

Conclusion:
Therefore, CBCT image guidance should be performed before SRS treatment to verify setup errors more accurately.

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