(Tuesday, 7/31/2018) 10:30 AM - 11:00 AM
Room: Exhibit Hall | Forum 5
Purpose: To evaluate the image quality parameters of planar and cone-beam CT (CBCT) for the On-Board Imaging (OBI) system of Varian True Beam and CBCT system of IBA proton gantry.
Methods: Evaluating image quality parameters of imaging systems is necessary to ensure accurate localization and visualization of target volumes. In this study, the IBA Primus-L phantom was used to acquire planar kV images with optimized kV/mAs settings for both Varian and IBA systems. Renormalized modulation transfer function (RMTF) at maximum spatial resolution was obtained and compared. Although small construction differences exist between the panel-detectors, the Varian OBI uses a bow-tie filter while IBA CBCT uses software to reduce the scattering factor. This leads to differences in the imaging quality between CBCTs. To quantify this, the CatPhan 604 phantom was used to optimize kV/mAs setting for optimal images and the following image quality parameters were compared: resolution/material, HU uniformity, and low contrast.
Results: Achieved spatial resolutions/RMTFs of Varian and IBA panel-detectors are 2.2 lp/mm with 10.4% and 2.5 lp/mm with 19.1%, respectively. For CBCT, a linear relationship between measured and actual HU of materials are seen in both system. F40 of RMTFs for Varian and IBA are 0.467 and 0.740, respectively. The bone and soft-tissue can be visually distinguished in both systems for positioning patients. But, non-compensated scattering X-rays in IBA CBCT results a non-smooth curve of modulation and spatial frequency, and an inferior low contrast detectability.
Conclusion: Although a better detectability and spatial resolution with large dynamic range of used panel-detector in IBA system, the effect of left-over scatted X-rays by software degrades its capability to disguising the tumor with around tissues. But, further improvement of software reduction can be easily conducted.
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