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Quality Assurance Baselines for the Integrated Imaging Systems On An Elekta Versa HD

L Poplawski

L Poplawski*, D Hyer , University of Iowa, Iowa City, IA


TU-C3-GePD-J(B)-5 (Tuesday, August 1, 2017) 10:30 AM - 11:00 AM Room: Joint Imaging-Therapy ePoster Lounge - B

Purpose: AAPM TG-142 recommends that spatial resolution, contrast, uniformity, and noise be evaluated and compared to a baseline on a monthly basis for all linear accelerator integrated imaging systems. In addition to these tests, cone-beam CT (CBCT) systems should also be evaluated for HU constancy. The purpose of this work was to identify robust baseline values and appropriate minimum performance levels for image quality of the XVI (kilovoltage-kV) and iView (megavoltage-MV) systems on two Elekta Versa HD accelerators with these recommendations in mind.

Methods: Baseline values were determined for each imaging system using the data trends over approximately a two-year period. For 2D imaging, the LEEDS TOR-18 phantom was imaged with a 120 kV/25 mA/40 ms/5 frame protocol and the QC3 phantom was imaged with a 2MU portal image. For the CBCT system, the CATPHAN CTP 503 was imaged with a 100 kV/40 mA/20 ms/183 frame protocol over a 200° arc. Analysis of all image quality phantoms was performed using RIT Image QA software. From these baseline values, minimum performance levels were quantified that allowed for normal monthly fluctuations.

Results: Based on the historical analysis of the image quality parameters, the following minimum performance levels were determined for the 2D kV system: spatial resolution ≥ 1 lp/mm and visualization of low contrast object number six (CNR > 3). For the 2D MV system: spatial resolution ≥ 0.75 lp/mm, CNR > 37.3, and noise < 327. For the CBCT system: spatial resolution ≥ 3.0 lp/cm, low contrast visibility < 2%, uniformity < 2%, and HU constancy of ±40HU from nominal levels for polystyrene and LDPE. Minimal variation between the two machines was noted.

Conclusion: The establishment of comprehensive minimum performance levels has ensured that the imaging systems are operating consistently while appropriately detecting degradation in image quality.

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