(Tuesday, 7/16/2019) 10:00 AM - 10:30 AM
Room: Exhibit Hall | Forum 9
Purpose: To evaluate the performance of the newly developed Catphan 606 phantom for MV CBCT and kV CBCT image quality assurance.
Methods: A newly developed Catphan 606 phantom (The Phantom Laboratory, Salem, NY) was used for image quality assurance of MV CBCT as well as kV CBCT. The phantom was tested on the Halcyon linear accelerator with MV and kV CBCT. The phantom was tested on the Halcyon linear accelerator with MV and kV CBCT. The phantom was accurately positioned at the virtual isocenter of the Halcyon and pushed to the beam isocenter, mimicking the procedure used for patient treatment. MV CBCT images were acquired for High Quality and Low Dose MV CBCT modes, and kV CBCT images with Head and Pelvis protocol with/without Iterative CBCT mode. The scanned image sets were processed, using a MatLab code, to determine pixel spacing (mm), HU linearity, slice thickness, and uniformity.
Results: Averaged slice thickness was the range of 2.5-2.8 for kV CBCT and 2.34-2.35 range for MV CBCT. For the CT number test, both MV CBCT images show a large deviation of 100-200 HU range on the high Z insert material and KV CBCT show good agreement. 2 kV CBCT images (Head and Pelvis) with iterative reconstruction method decreases the noise with 47.8 to 24.0 HU(Head), and 9.1 to 5.4 HU(Pelvis) compared to standard CBCT reconstruction. For the uniformity test, the largest absolute HU difference between 5 ROIs reported and 2 MV CBCT was 31.1 and 28.9 HU for high quality and low dose modes respectively. 4 kV CBCT images showed a relatively uniform response (5.3 - 11.3 HU) across the homogeneous area.
Conclusion: The performance of new Catphan 606 for MV CBCT and kV CBCT beam on the Halcyon System evaluated and established tolerances for routine CBCT image QA.
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