Abstract

Machine learning (ML) algorithms for selecting and combining radiomic features into multiparametric prediction models have become popular; however, it has been shown that large variations in performance can be obtained by relying on different approaches. The purpose of this study was to evaluate the potential benefit of combining different algorithms into an improved consensus for the final prediction, as it has been shown in other fields. Methods: The evaluation was carried out in the context of the use of radiomics from 18F-FDG PET/CT images for predicting outcome in stage II-III Non-Small Cell Lung Cancer. A cohort of 138 patients was exploited for the present analysis. Eighty-seven patients had been previously recruited retrospectively for another study and were used here for training and internal validation. We also used data from prospectively recruited patients (n = 51) for testing. Three different machine learning pipelines relying on embedded feature selection were trained to predict overall survival (OS) as a binary classification: Support Vector machines (SVMs), Random Forests (RFs), and Logistic Regression (LR). Two different clinical endpoints were investigated: median OS or OS shorter than 6 months. The fusion of the three approaches was implemented using two different strategies: majority voting on the binary outputs or averaging of the output probabilities. Results: Our results confirm previous findings, highlighting that different ML pipelines select different sets of features and reach different classification performances (accuracy in the testing set ranging between 63% and 67% for median OS, and between 75% and 80% for OS < 6 months). Generating a consensus improved the performance for both endpoints; with the probabilities averaging strategy outperforming the majority voting (accuracy of 78% vs. 71% for median OS and 89 vs. 84% for OS < 6 months). Overall, the performance of these radiomic-based models outperformed the standard clinical staging in both endpoints (accuracy of 58% and 53% accuracy in the testing set for each endpoint). Conclusion: Although obtained in a small cohort of patients, our results suggest that a consensus of machine learning algorithms can improve performance in the context of radiomics. The resulting prognostic stratification in the prospective testing cohort is higher than when relying on the clinical stage. This could be of interest for clinical practice as it could help to identify patients with higher risk amongst stage II and III patients, who could benefit from intensified treatment and/or more frequent follow-up after treatment.

Highlights

  • Non-small cell lung cancer (NSCLC) remains a deadly disease, despite improvements in diagnosis, staging and treatment

  • We showed that PET and CT radiomic features can have complementary value over stage alone in NSCLC stage II-III, relying on standard statistical analysis and exploiting a retrospective-only cohort of patients [13]

  • As previously shown in the retrospectively collected cohort (n = 116), patients with stage I have a much more favorable prognosis compared to these with stages II and III, and radiomic features have more potential to discriminate between patients with better or worse prognosis amongst stage II-III patients [13]

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Summary

Introduction

Non-small cell lung cancer (NSCLC) remains a deadly disease, despite improvements in diagnosis, staging and treatment. Like stage, age, and extent of resection after surgery [3], together with PET and/or CT image-derived engineered features, such as the histogram intensity metrics, tumor geometric shape descriptors or intra-tumor heterogeneity textural features, have been associated with prognosis [4,5]. The extraction of these features through a semi-automated workflow is known today as radiomics [6]

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