title: Evaluation of imaging performance of megavoltage cone-beam CT over an extended period.
abstract: A linear accelerator vendor and the AAPM TG-142 report propose that quality assurance testing for image-guided devices such megavoltage cone-beam CT (MV-CBCT) be conducted on a monthly basis. In clinical settings, however, unpredictable errors such as image artifacts can occur even when quality assurance results performed at this frequency are within tolerance limits. Here, we evaluated the imaging performance of MV-CBCT on a weekly basis for ∼ 1 year using a Siemens ONCOR machine with a 6-MV X-ray and an image-quality phantom. Image acquisition was undertaken using 15 monitor units. Geometric distortion was evaluated with beads evenly distributed in the phantom, and the results were compared with the expected position in three dimensions. Image-quality characteristics of the system were measured and assessed qualitatively and quantitatively, including image noise and uniformity, low-contrast resolution, high-contrast resolution and spatial resolution. All evaluations were performed 100 times each. For geometric distortion, deviation between the measured and expected values was within the tolerance limit of 2 mm. However, a subtle systematic error was found which meant that the phantom was rotated slightly in a clockwise manner, possibly due to geometry calibration of the MV-CBCT system. Regarding image noise and uniformity, two incidents over tolerance occurred in 100 measurements. This phenomenon disappeared after dose calibration of beam output for MV-CBCT. In contrast, all results for low-contrast resolution, high-contrast resolution and spatial resolution were within their respective tolerances.
authors: Department of Oral and Maxillofacial Radiology, Osaka University Graduate School of Dentistry, 1-8 Yamada-oka, Suita, Osaka, 565-0871, Japan.
authors: Iori
authors: I
authors: Sumida
authors: Hajime
authors: H
authors: Yamaguchi
authors: Hisao
authors: H
authors: Kizaki
authors: Yuji
authors: Y
authors: Yamada
authors: Masahiko
authors: M
authors: Koizumi
authors: Yasuo
authors: Y
authors: Yoshioka
authors: Kazuhiko
authors: K
authors: Ogawa
authors: Naoya
authors: N
authors: Kakimoto
authors: Shumei
authors: S
authors: Murakami
authors: Souhei
authors: S
authors: Furukawa
mesh_terms: D016477:Artifacts; D054893:Cone-Beam Computed Tomography / Q000295:instrumentation*; D004867:Equipment Design; D019544:Equipment Failure Analysis; D019047:Phantoms, Imaging; D011857:Radiographic Image Interpretation, Computer-Assisted / Q000295:instrumentation*; D061089:Radiotherapy, Image-Guided / Q000295:instrumentation*; D015203:Reproducibility of Results; D012680:Sensitivity and Specificity; D013997:Time Factors
keywords: Cone-beam CT; IGRT; QA; calibration; image-guided radiation therapy; tolerance
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