Technical Note: An IBEX adaption toward image biomarker standardization

Purpose: Interest in the field of radiomics is rapidly growing because of its potential to characterize tumor phenotype and provide predictive and prognostic information. Nevertheless, the reproducibility and robustness of radiomics studies are hampered by the lack of standardization in feature definition and calculation. In the context of the image biomarker standardization initiative (IBSI), we investigated the grade of compliance of the image biomarker explorer (IBEX), a free open-source radiomic software, and we developed and validated standardized-IBEX (S-IBEX), an adaptation of IBEX to IBSI. Methods: Image biomarker explorer source code was checked against IBSI standard. Both the feature implementation and the overall image preprocessing chain were evaluated. Sections were re-implemented wherever differences emerged: in particular, contour-to-binary-mask conversion, image sub-portion extraction, re-segmentation, gray-level discretization and interpolation were aligned to IBSI. All reported IBSI features were implemented in S-IBEX. On a patient phantom, S-IBEX was validated by benchmarking five different preprocessing configurations proposed by IBSI. Results: Most IBEX feature definitions are IBSI compliant; however, IBEX preprocessing introduces non-negligible nonconformities, resulting in feature values not aligned with the corresponding IBSI benchmarks. On the contrary, S-IBEX features are in agreement with the standard regardless of preprocessing configurations: the percentage of features equal to their benchmark values ranges from 98.1% to 99.5%, with overall maximum percentage error below 1%. Moreover, the impact of noncompliant preprocessing steps has been assessed: in these cases, the percentage of features equal to the standard drops below 35%. Conclusions: The use of standardized software for radiomic feature extraction is essential to ensure the reproducibility of results across different institutions, easing at the same time their external validation. This work presents and validates S-IBEX, a free IBSI-compliant software, developed upon IBEX, for feature extraction that is both easy to use and quantitatively accurate.