Abstract
PurposeThe aim of this study was to develop Quality Assurance procedures for the BrainLab ExacTrac (ET) imaging system following the TG 142 recommendations for planar kV imaging systems.Materials and MethodsA custom‐designed 3D printed holder was used to position the Standard Imaging QCkV‐1 phantom at isocenter, facing the ET X ray tubes. The linac's light field (collimator at 45⁰) was used to position the phantom holder. The ET images were exported to ARIA where geometric distortion was checked. The DICOM images were analyzed in the PIPSpro software. The following parameters were recorded (technique 80 kV/2mAs): spatial resolution (Modulated Transfer Function (MTF) F50/F40/F30), contrast‐to‐noise ratio (CNR), and noise. A baseline was generated for future image analysis. Beam quality and exposure were measured using the Unfors R/F detector. Using a rod holder, the detector was placed at isocenter, facing each ET X‐ray tube. The measurements were performed for all preset protocols ranging from cranial low (80 kV/6.3 mAs) to abdomen high (145 kV/25 mAs). The total exposure was converted to dose.Results and DiscussionThe image quality parameters were close for the two tubes. A common baseline was therefore generated. The average baseline values (both tubes, both images/tube) were 1.06/1.18/1.30, 1.32, and 67.3 for the MTF F50/F40/F30, noise, and CNR respectively. The procedure described here was used for another 24 sets. Using a positioning template and 3D printed phantom holder, experimental reproducibility has been acceptably high. The measured phantom dimensions were within 1 mm from the nominal values. The measured kV values were within 2% of the nominal values. The exposure values for the two tubes were comparable. The range of total measured dose was 0.099 mGy (cranial low) to 1.353 mGy (abdomen high).ConclusionsA reliable process has been implemented for QA of the ET imaging system by characterizing the system's performance at isocenter, consistent with clinical conventions.
Highlights
The BrainLab ExacTrac (ET) X ray 6D stereotactic IGRT system (BrainLab AG, Feldkirchen, Germany) could play an important role in image-guided radiosurgery and radiotherapy,[1,2] on the assumption that the image quality is reliably good. This system is an integration of two subsystems: an infrared-based optical positioning system for initial patient setup and couch movement control and a radiographic kV X ray imaging system for position verification and readjustments based on internal anatomy or implanted fiducials
This study presents the quality assurance (QA) program we developed and the tolerance values we established for the ET imaging quality parameters
Photo showing the setup for the ExacTrac Annual Quality Assurance (ET AQA) testing
Summary
The BrainLab ExacTrac (ET) X ray 6D stereotactic IGRT system (BrainLab AG, Feldkirchen, Germany) could play an important role in image-guided radiosurgery and radiotherapy,[1,2] on the assumption that the image quality is reliably good. This system is an integration of two subsystems: an infrared-based optical positioning system for initial patient setup and couch movement control and a radiographic kV X ray imaging system for position verification and readjustments based on internal anatomy or implanted fiducials. The BrainLab Novalis ExacTrac system is listed in the AAPM Task Group Report 75 (TG 75)[4] focusing on image dose management during image-guided radiotherapy, and the dose for two extreme techniques (cranium/Cspine and body-thoracic/lumbar spine) are tabulated, without describing the measurement methodology
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