Program Information
Daily Quality Assurance of Coincidence Between Imaging and Radiation Isocenter
Y Huang*, B Zhao , I Chetty , J Gordon , N Wen , Henry Ford Health System, Detroit, MI
Presentations
PO-BPC-Exhibit Hall-8 (Saturday, March 7, 2015) Room: Exhibit Hall
Purpose:
The targeting accuracy of an image guided treatment depends crucially on the coincidence between imaging and radiation isocenter. In this study, we developed and implemented an efficient quality assurance (QA) procedure that measures the coincidence between imaging and radiation isocenter daily.
Methods:
A two-step procedure was implemented on a Novalisâ„¢ Tx. First, four Winston Lutz (WL) portal images at gantry angles of 0, 90°, 180°, and 270° are acquired of a BB that is positioned according to laser or light field close to machine isocenter, the analysis of which provides the offset of the BB relative to the average radiation isocenter (Vâ‚). Next, the BB was imaged with the ExacTracâ„¢ X-ray (V6.0.5, Brainlab AG) or cone beam computed tomography (CBCT) of the OBIâ„¢ system (V1.5, Varian Medical Systems), the analysis of which provides the offset of the BB relative to imaging isocenter (Vâ‚‚). The vector, Vâ‚‚-Vâ‚, is then the deviation between the imaging and radiation isocenter.
Results:
Averaged over a period of a month, the overall deviation to the average radiation isocenter (μ±σ) is (0.17±0.10) mm for the ExacTrac™ X-ray system and (0.51±0.26) mm for the OBI™ CBCT on the Novalis™ Tx.
Conclusion: Both ExacTracâ„¢ X-ray and OBIâ„¢ CBCT isocenters on the Novalisâ„¢ Tx are reproducible and closely match the average radiation isocenter. The congruency between imaging and radiation isocenters can be efficiently measured as part of daily QA program to ensure accurate patient positioning.
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