Dennis Nichols Stanley, Nikos Papanikolaou, Alonso N Gutierrez
Cite this article as: Stanley DN, Papanikolaou N, Gutierrez AN. An evaluation of the stability of image quality parameters of Varian on-board imaging (OBI) and EPID imaging systems. Int J Cancer Ther Oncol 2014; 2(2):020236.
[Presented at the Young Investigator’s Symposium at the 2014 Annual Meeting of Southwest Chapter of American Association of Physicists in Medicine (AAPM) in San Antonio, Texas, USA]
Purpose: Quality assurance of the image quality for image guided localization systems is crucial to ensure accurate visualization and localization of target volumes. In this study, the stability of selected image parameters was assessed and evaluated for CBCT mode, planar radiographic kV mode and the radiographic MV EPID mode.
Methods: The CATPHAN, QckV-1 and QC-3 phantoms were used to evaluate the image quality parameters. The planar radiographic images were analyzed in PIPSpro™ with spatial resolution (f30, f40, f50) being recorded. For OBI CBCT, High quality head Full-Fan acquisition and Pelvis Half-Fan acquisition modes were evaluated for Uniformity, Noise, Spatial Resolution, HU constancy and geometric distortion. Dose and kVp for the OBI were recorded using the Unfors RaySafe Xi system with the R/F High Detector for planar kV and the CT detector for CBCT. Dose for the MV EPID was recorded using a PTW975 Semiflex Ion Chamber, webline electrometer and 1cm SolidWater™.
Results: For each metric, values were normalized to the mean and the standard deviations were recorded. Table 1 shows the standard deviation for all results. Using this, tolerances can be reported as a warning threshold of 1σ and an action threshold of 2σ. Table 2 shows the warning and action tolerances for the planar radiographic modalities while Table 3 and 4 show tolerance levels for the Full-Fan and Half-Fan, respectively.
Conclusion: A study was performed to assess the stability of the basic image quality parameters recommended by TG-142 for the Varian OBI and EPID Imaging systems. The two systems show consistent imaging and dosimetric properties over the evaluated time frame.