Effect of the Small Field of View and Imaging Parameters to Image Quality and Dose Calculation in Adaptive Radiotherapy

Abstract

Abstract Background The use of cone beam computed tomography (CBCT) for dose calculation in adaptive radiotherapy has been investigated in many studies. Proper acquisition and reconstruction of preset parameters could improve the accuracy of dose calculation based on CBCT images. This study evaluated the impact of the modified image acquisition and preset reconstruction parameter available in X-Ray Volumetric Imaging (XVI) to improve CBCT image quality and dose calculation accuracy. Materials and methods Calibration curves were generated by scanning the CIRS phantom using CBCT XVI Elekta 5.0.4 and Computed Tomography (CT) Simulator Somatom, which served as CT image reference. Rando and Catphan 503 phantoms were scanned with various acquisition and reconstruction parameters for dose accuracy and image quality tests. The image quality test is uniformity, low contrast visibility, spatial resolution, and geometrical scale test for each image by following the XVI image quality test module. Results Acquisition and reconstruction parameters have an impact on the Hounsfield Unit (HU) value that is used as the HU-Relative Electron Density (RED) calibration curve. The dose difference for all the calibration curves was within 1% and passed the gamma passing rate. Images acquired using 120 kVp, F1 (with Bowtie Filter), and 50 mA (F1-120-50-10) scored the highest Gamma Index (GI) of 98.5%. For the image quality test, it scored 1.20% on the uniformity test, 2.14% on the low contrast visibility test, and 11 lp/cm on the spatial resolution test. However, F1-120-50-10 reconstructed with different reconstructions scored 3.83% and 4 lp/cm in contrast and spatial resolution test, respectively. Conclusion CBCT reconstruction parameters work as a scatter correction. It could improve the dose accuracy and image quality. Nevertheless, without adequate CBCT acquisition protocols, it would produce an image with high uncertainty and cannot be fixed with reconstruction protocols. The F1-120-50-10 protocols generate the highest dose accuracy and image quality.