Program Information
Development of Clinically Relevant QA Procedures for the BrainLab ExacTrac Imaging System
P Halvorsen*, I Iftimia , Lahey Hospital and Medical Center, Burlington, MA
Presentations
MO-RPM-GePD-T-3 (Monday, July 31, 2017) 3:45 PM - 4:15 PM Room: Therapy ePoster Lounge
Purpose: To develop QA procedures for the ExacTrac (ET) imaging system following the TG 142 recommendations.
Methods: A custom-designed 3D printed holder was used to position the QCkV-1 phantom at isocenter, facing the ET X-ray tubes (i.e., rotated 45⁰ in both horizontal and vertical planes). The linac’s light field (collimator at 45⁰) was used to position the phantom holder. The ET images in DICOM format were exported to ARIA where geometric distortion was checked. The DICOM images were analyzed in the PIPSpro software. Multiple images were acquired for each tube (80kV/2mAs) to determine if the parameters of interest are comparable for the two tubes. A baseline was generated for future image analysis. The following parameters were recorded: spatial resolution (MTF F50/F40/F30), contrast-to-noise ratio (CNR), and noise.Beam quality and exposure were measured using the Unfors RaySafe detector. Using a holder, the detector was placed at isocenter, facing each ET X-ray tube (see above). The measurements were performed for all preset protocols ranging from cranial low (80kV/6.3mAs) to abdomen high (140kV/25mAs). The total exposure (from both tubes) was converted to dose.
Results: The image quality parameters were very close for the two tubes. A common baseline was therefore generated. The average values were 1.06/1.18/1.30, 66.63, and 1.31 for F50/F40/F30, CNR, and noise, respectively. The measured phantom dimensions were within 1 mm from the nominal values.The measured kV values were within 4% of the nominal values. The exposure values for the two tubes were comparable. The range of total measured dose was 0.106 mGy (cranial low) to 1.301 mGy (abdomen high).
Conclusion: A simple process has been implemented for QA of the ET imaging system by characterizing the system’s performance at isocenter, consistent with clinical conventions.Future work will focus on PIPSpro “single image method” and raw versus DICOM image analysis.
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