Purpose: The RefleXion® X1 is a novel radiotherapy delivery system on a ring gantry equipped with fan-beam kV-CT and PET imaging subsystems. The day-to-day scanning variability of radiomics features must be evaluated to warrant the accuracy of models using radiomics features. This study aims to establish the technical validation of the reproducibility of radiomic features produced by the X1 kV-CT.
Methods: The CCR phantom includes six cartridges of different materials. It was scanned ten-times on the X1 system over a three-month time frame using the two most frequently used scanning protocols. 1026 and 66 radiomic features were extracted from each of the six cartridges using two IBSI-compliant radiomics software packages, respectively. Linear regression analysis was performed to evaluate the repeatability and reproducibility over time. T-test for the difference in the mean and F-test for the difference in standard deviation was used to compare the radiomics features between scanning techniques.
Results: There was no strong linear relationship between radiomic features and elapsed days. Based on linear regression analysis between the radiomic features and the number of elapsed days, the fitted coefficient was less than 0.02 for all 1026 radiomic features and R2 < 0.05 in all regression analysis. 66 of the 1026 radiomic features exceeded 10% in coefficient of variance. A comparison of radiomic features showed statistically significant differences between the fast and slow scan protocols (two-tailed p-value < 0.05 in paired t-tests), consistent with published reports.
Conclusion: Radiomic analysis using two different software packages demonstrated that the clinically useful CT radiomic features produced by the X1 are reproducible and stable over time, demonstrating its utility as a quantitative imaging platform. The CT radiomic features produced by the X1 may vary with the scanning protocols, demonstrating the necessity of using consistent scan protocols to monitor radiomic features throughout the treatment course.